Documented -ignore_readdir_race and -noignore_readdir_race

[findutils.git] / doc / find.texi

\input texinfo @c -*-texinfo-*-
@c %**start of header
@setfilename find.info
@settitle Finding Files
@c For double-sided printing, uncomment:
@c @setchapternewpage odd
@c %**end of header

@include version.texi

@iftex
@finalout
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@ifinfo
@format
START-INFO-DIR-ENTRY
* Finding Files: (find).        Listing and operating on files
                                that match certain criteria.
END-INFO-DIR-ENTRY
@end format

This file documents the GNU utilities for finding files that match
certain criteria and performing various operations on them.

Copyright (C) 1994 Free Software Foundation, Inc.

Permission is granted to make and distribute verbatim copies of
this manual provided the copyright notice and this permission notice
are preserved on all copies.

@ignore
Permission is granted to process this file through TeX and print the
results, provided the printed document carries copying permission
notice identical to this one except for the removal of this paragraph
(this paragraph not being relevant to the printed manual).

@end ignore
Permission is granted to copy and distribute modified versions of this
manual under the conditions for verbatim copying, provided that the entire
resulting derived work is distributed under the terms of a permission
notice identical to this one.

Permission is granted to copy and distribute translations of this manual
into another language, under the above conditions for modified versions,
except that this permission notice may be stated in a translation approved
by the Foundation.
@end ifinfo

@titlepage
@title Finding Files
@subtitle Edition @value{EDITION}, for GNU @code{find} version @value{VERSION}
@subtitle @value{UPDATED}
@author by David MacKenzie

@page
@vskip 0pt plus 1filll
Copyright @copyright{} 1994 Free Software Foundation, Inc.

Permission is granted to make and distribute verbatim copies of
this manual provided the copyright notice and this permission notice
are preserved on all copies.

Permission is granted to copy and distribute modified versions of this
manual under the conditions for verbatim copying, provided that the entire
resulting derived work is distributed under the terms of a permission
notice identical to this one.

Permission is granted to copy and distribute translations of this manual
into another language, under the above conditions for modified versions,
except that this permission notice may be stated in a translation approved
by the Foundation.
@end titlepage

@node Top, Introduction, , (dir)
@comment  node-name,  next,  previous,  up

@ifinfo
This file documents the GNU utilities for finding files that match
certain criteria and performing various actions on them.
This is edition @value{EDITION}, for @code{find} version @value{VERSION}.
@end ifinfo

@c The master menu, created with texinfo-master-menu, goes here.

@menu
* Introduction::                Summary of the tasks this manual describes.
* Finding Files::               Finding files that match certain criteria.
* Actions::                     Doing things to files you have found.
* Common Tasks::                Solutions to common real-world problems.
* Databases::                   Maintaining file name databases.
* File Permissions::            How to control access to files.
* Reference::                   Summary of how to invoke the programs.
* Primary Index::               The components of @code{find} expressions.
@end menu

@node Introduction, Finding Files, Top, Top
@chapter Introduction

This manual shows how to find files that meet criteria you specify, and
how to perform various actions on the files that you find.  The
principal programs that you use to perform these tasks are @code{find},
@code{locate}, and @code{xargs}.  Some of the examples in this manual
use capabilities specific to the GNU versions of those programs.

GNU @code{find} was originally written by Eric Decker, with enhancements
by David MacKenzie, Jay Plett, and Tim Wood.  GNU @code{xargs} was
originally written by Mike Rendell, with enhancements by David
MacKenzie.  GNU @code{locate} and its associated utilities were
originally written by James Woods, with enhancements by David MacKenzie.
The idea for @samp{find -print0} and @samp{xargs -0} came from Dan
Bernstein.  Many other people have contributed bug fixes, small
improvements, and helpful suggestions.  Thanks!

Mail suggestions and bug reports for these programs to
@code{bug-findutils@@gnu.org}.  Please include the version
number, which you can get by running @samp{find --version}.

@menu
* Scope::
* Overview::
* find Expressions::
@end menu

@node Scope
@section Scope

For brevity, the word @dfn{file} in this manual means a regular file, a
directory, a symbolic link, or any other kind of node that has a
directory entry.  A directory entry is also called a @dfn{file name}.  A
file name may contain some, all, or none of the directories in a path
that leads to the file.  These are all examples of what this manual
calls ``file names'':

@example
parser.c
README
./budget/may-94.sc
fred/.cshrc
/usr/local/include/termcap.h
@end example

A @dfn{directory tree} is a directory and the files it contains, all of
its subdirectories and the files they contain, etc.  It can also be a
single non-directory file.

These programs enable you to find the files in one or more directory
trees that:

@itemize @bullet
@item
have names that contain certain text or match a certain pattern;
@item
are links to certain files;
@item
were last used during a certain period of time;
@item
are within a certain size range;
@item
are of a certain type (regular file, directory, symbolic link, etc.);
@item
are owned by a certain user or group;
@item
have certain access permissions;
@item
contain text that matches a certain pattern;
@item
are within a certain depth in the directory tree;
@item
or some combination of the above.
@end itemize

Once you have found the files you're looking for (or files that are
potentially the ones you're looking for), you can do more to them than
simply list their names.  You can get any combination of the files'
attributes, or process the files in many ways, either individually or in
groups of various sizes.  Actions that you might want to perform on the
files you have found include, but are not limited to:

@itemize @bullet
@item
view or edit
@item
store in an archive
@item
remove or rename
@item
change access permissions
@item
classify into groups
@end itemize

This manual describes how to perform each of those tasks, and more.

@node Overview
@section Overview

The principal programs used for making lists of files that match given
criteria and running commands on them are @code{find}, @code{locate},
and @code{xargs}.  An additional command, @code{updatedb}, is used by
system administrators to create databases for @code{locate} to use.

@code{find} searches for files in a directory hierarchy and prints
information about the files it found.  It is run like this:

@example
find @r{[}@var{file}@dots{}@r{]} @r{[}@var{expression}@r{]}
@end example

@noindent
Here is a typical use of @code{find}.  This example prints the names of
all files in the directory tree rooted in @file{/usr/src} whose name
ends with @samp{.c} and that are larger than 100 Kilobytes.
@example
find /usr/src -name '*.c' -size +100k -print
@end example

@code{locate} searches special file name databases for file names that
match patterns.  The system administrator runs the @code{updatedb}
program to create the databases.  @code{locate} is run like this:

@example
locate @r{[}@var{option}@dots{}@r{]} @var{pattern}@dots{}
@end example

@noindent
This example prints the names of all files in the default file name
database whose name ends with @samp{Makefile} or @samp{makefile}.  Which
file names are stored in the database depends on how the system
administrator ran @code{updatedb}.
@example
locate '*[Mm]akefile'
@end example

The name @code{xargs}, pronounced EX-args, means ``combine arguments.''
@code{xargs} builds and executes command lines by gathering together
arguments it reads on the standard input.  Most often, these arguments
are lists of file names generated by @code{find}.  @code{xargs} is run
like this:

@example
xargs @r{[}@var{option}@dots{}@r{]} @r{[}@var{command} @r{[}@var{initial-arguments}@r{]}@r{]}
@end example

@noindent
The following command searches the files listed in the file
@file{file-list} and prints all of the lines in them that contain the
word @samp{typedef}.
@example
xargs grep typedef < file-list
@end example

@node find Expressions
@section @code{find} Expressions

The expression that @code{find} uses to select files consists of one or
more @dfn{primaries}, each of which is a separate command line argument
to @code{find}.  @code{find} evaluates the expression each time it
processes a file.  An expression can contain any of the following types
of primaries:

@table @dfn
@item options
affect overall operation rather than the processing of a specific file;
@item tests
return a true or false value, depending on the file's attributes;
@item actions
have side effects and return a true or false value; and
@item operators
connect the other arguments and affect when and whether they are
evaluated.
@end table

You can omit the operator between two primaries; it defaults to
@samp{-and}.  @xref{Combining Primaries With Operators}, for ways to
connect primaries into more complex expressions.  If the expression
contains no actions other than @samp{-prune}, @samp{-print} is performed
on all files for which the entire expression is true (@pxref{Print File
Name}).

Options take effect immediately, rather than being evaluated for each
file when their place in the expression is reached.  Therefore, for
clarity, it is best to place them at the beginning of the expression.

Many of the primaries take arguments, which immediately follow them in
the next command line argument to @code{find}.  Some arguments are file
names, patterns, or other strings; others are numbers.  Numeric
arguments can be specified as

@table @code
@item +@var{n}
for greater than @var{n},
@item -@var{n}
for less than @var{n},
@item @var{n}
for exactly @var{n}.
@end table

@node Finding Files, Actions, Introduction, Top
@chapter Finding Files

By default, @code{find} prints to the standard output the names of the
files that match the given criteria.  @xref{Actions}, for how to get more
information about the matching files.

@menu
* Name::
* Links::
* Time::
* Size::
* Type::
* Owner::
* Permissions::
* Contents::
* Directories::
* Filesystems::
* Combining Primaries With Operators::
@end menu

@node Name
@section Name

Here are ways to search for files whose name matches a certain pattern.
@xref{Shell Pattern Matching}, for a description of the @var{pattern}
arguments to these tests.

Each of these tests has a case-sensitive version and a case-insensitive
version, whose name begins with @samp{i}.  In a case-insensitive
comparison, the patterns @samp{fo*} and @samp{F??} match the file names
@file{Foo}, @samp{FOO}, @samp{foo}, @samp{fOo}, etc.

@menu
* Base Name Patterns::
* Full Name Patterns::
* Fast Full Name Search::
* Shell Pattern Matching::      Wildcards used by these programs.
@end menu

@node Base Name Patterns
@subsection Base Name Patterns

@deffn Test -name pattern
@deffnx Test -iname pattern
True if the base of the file name (the path with the leading directories
removed) matches shell pattern @var{pattern}.  For @samp{-iname}, the
match is case-insensitive.  To ignore a whole directory tree, use
@samp{-prune} (@pxref{Directories}).  As an example, to find Texinfo
source files in @file{/usr/local/doc}:

@example
find /usr/local/doc -name '*.texi'
@end example
@end deffn

@node Full Name Patterns
@subsection Full Name Patterns

@deffn Test -path pattern
@deffnx Test -ipath pattern
True if the entire file name, starting with the command line argument
under which the file was found, matches shell pattern @var{pattern}.
For @samp{-ipath}, the match is case-insensitive.  To ignore a whole
directory tree, use @samp{-prune} rather than checking every file in the
tree (@pxref{Directories}).
@end deffn

@deffn Test -regex expr
@deffnx Test -iregex expr
True if the entire file name matches regular expression @var{expr}.
This is a match on the whole path, not a search.  For example, to match
a file named @file{./fubar3}, you can use the regular expression
@samp{.*bar.} or @samp{.*b.*3}, but not @samp{b.*r3}.  @xref{Regexps, ,
Syntax of Regular Expressions, emacs, The GNU Emacs Manual}, for a
description of the syntax of regular expressions.  For @samp{-iregex},
the match is case-insensitive.
@end deffn

@node Fast Full Name Search
@subsection Fast Full Name Search

To search for files by name without having to actually scan the
directories on the disk (which can be slow), you can use the
@code{locate} program.  For each shell pattern you give it,
@code{locate} searches one or more databases of file names and displays
the file names that contain the pattern.  @xref{Shell Pattern Matching},
for details about shell patterns.

If a pattern is a plain string---it contains no
metacharacters---@code{locate} displays all file names in the database
that contain that string.  If a pattern contains
metacharacters, @code{locate} only displays file names that match the
pattern exactly.  As a result, patterns that contain metacharacters
should usually begin with a @samp{*}, and will most often end with one
as well.  The exceptions are patterns that are intended to explicitly
match the beginning or end of a file name.

The command
@example
locate @var{pattern}
@end example

is almost equivalent to
@example
find @var{directories} -name @var{pattern}
@end example

where @var{directories} are the directories for which the file name
databases contain information.  The differences are that the
@code{locate} information might be out of date, and that @code{locate}
handles wildcards in the pattern slightly differently than @code{find}
(@pxref{Shell Pattern Matching}).

The file name databases contain lists of files that were on the system
when the databases were last updated.  The system administrator can
choose the file name of the default database, the frequency with which
the databases are updated, and the directories for which they contain
entries.

Here is how to select which file name databases @code{locate} searches.
The default is system-dependent.

@table @code
@item --database=@var{path}
@itemx -d @var{path}
Instead of searching the default file name database, search the file
name databases in @var{path}, which is a colon-separated list of
database file names.  You can also use the environment variable
@code{LOCATE_PATH} to set the list of database files to search.  The
option overrides the environment variable if both are used.
@end table

@node Shell Pattern Matching
@subsection Shell Pattern Matching

@code{find} and @code{locate} can compare file names, or parts of file
names, to shell patterns.  A @dfn{shell pattern} is a string that may
contain the following special characters, which are known as
@dfn{wildcards} or @dfn{metacharacters}.

You must quote patterns that contain metacharacters to prevent the shell
from expanding them itself.  Double and single quotes both work; so does
escaping with a backslash.

@table @code
@item *
Matches any zero or more characters.

@item ?
Matches any one character.

@item [@var{string}]
Matches exactly one character that is a member of the string
@var{string}.  This is called a @dfn{character class}.  As a shorthand,
@var{string} may contain ranges, which consist of two characters with a
dash between them.  For example, the class @samp{[a-z0-9_]} matches a
lowercase letter, a number, or an underscore.  You can negate a class by
placing a @samp{!} or @samp{^} immediately after the opening bracket.
Thus, @samp{[^A-Z@@]} matches any character except an uppercase letter
or an at sign.

@item \
Removes the special meaning of the character that follows it.  This
works even in character classes.
@end table

In the @code{find} tests that do shell pattern matching (@samp{-name},
@samp{-path}, etc.), wildcards in the pattern do not match a @samp{.}
at the beginning of a file name.  This is not the case for
@code{locate}.  Thus, @samp{find -name '*macs'} does not match a file
named @file{.emacs}, but @samp{locate '*macs'} does.

Slash characters have no special significance in the shell pattern
matching that @code{find} and @code{locate} do, unlike in the shell, in
which wildcards do not match them.  Therefore, a pattern @samp{foo*bar}
can match a file name @samp{foo3/bar}, and a pattern @samp{./sr*sc} can
match a file name @samp{./src/misc}.

@node Links
@section Links

There are two ways that files can be linked together.  @dfn{Symbolic
links} are a special type of file whose contents are a portion of the
name of another file.  @dfn{Hard links} are multiple directory entries
for one file; the file names all have the same index node (@dfn{inode})
number on the disk.

@menu
* Symbolic Links::
* Hard Links::
@end menu

@node Symbolic Links
@subsection Symbolic Links

@deffn Test -lname pattern
@deffnx Test -ilname pattern
True if the file is a symbolic link whose contents match shell pattern
@var{pattern}.  For @samp{-ilname}, the match is case-insensitive.
@xref{Shell Pattern Matching}, for details about the @var{pattern}
argument.  So, to list any symbolic links to @file{sysdep.c} in the
current directory and its subdirectories, you can do:

@example
find . -lname '*sysdep.c'
@end example
@end deffn

@deffn Option -follow
Dereference symbolic links.  The following differences in behavior occur
when this option is given:

@itemize @bullet
@item
@code{find} follows symbolic links to directories when searching
directory trees.
@item
@samp{-lname} and @samp{-ilname} always return false.
@item
@samp{-type} reports the types of the files that symbolic links point
to.
@item
Implies @samp{-noleaf} (@pxref{Directories}).
@end itemize
@end deffn

@node Hard Links
@subsection Hard Links

To find hard links, first get the inode number of the file whose links
you want to find.  You can learn a file's inode number and the number of
links to it by running @samp{ls -i} or @samp{find -ls}.  If the file has
more than one link, you can search for the other links by passing that
inode number to @samp{-inum}.  Add the @samp{-xdev} option if you are
starting the search at a directory that has other filesystems mounted on
it, such as @file{/usr} on many systems.  Doing this saves needless
searching, since hard links to a file must be on the same filesystem.
@xref{Filesystems}.

@deffn Test -inum n
File has inode number @var{n}.
@end deffn

You can also search for files that have a certain number of links, with
@samp{-links}.  Directories normally have at least two hard links; their
@file{.} entry is the second one.  If they have subdirectories, each of
those also has a hard link called @file{..} to its parent directory.

@deffn Test -links n
File has @var{n} hard links.
@end deffn

@node Time
@section Time

Each file has three time stamps, which record the last time that certain
operations were performed on the file:

@enumerate
@item
access (read the file's contents)
@item
change the status (modify the file or its attributes)
@item
modify (change the file's contents)
@end enumerate

You can search for files whose time stamps are within a certain age
range, or compare them to other time stamps.

@menu
* Age Ranges::
* Comparing Timestamps::
@end menu

@node Age Ranges
@subsection Age Ranges

These tests are mainly useful with ranges (@samp{+@var{n}} and
@samp{-@var{n}}).

@deffn Test -atime n
@deffnx Test -ctime n
@deffnx Test -mtime n
True if the file was last accessed (or its status changed, or it was
modified) @var{n}*24 hours ago.
@end deffn

@deffn Test -amin n
@deffnx Test -cmin n
@deffnx Test -mmin n
True if the file was last accessed (or its status changed, or it was
modified) @var{n} minutes ago.  These tests provide finer granularity of
measurement than @samp{-atime} et al.  For example, to list files in
@file{/u/bill} that were last read from 2 to 6 minutes ago:

@example
find /u/bill -amin +2 -amin -6
@end example
@end deffn

@deffn Option -daystart
Measure times from the beginning of today rather than from 24 hours ago.
So, to list the regular files in your home directory that were modified
yesterday, do

@example
find ~ -daystart -type f -mtime 1
@end example
@end deffn

@node Comparing Timestamps
@subsection Comparing Timestamps

As an alternative to comparing timestamps to the current time, you can
compare them to another file's timestamp.  That file's timestamp could
be updated by another program when some event occurs.  Or you could set
it to a particular fixed date using the @code{touch} command.  For
example, to list files in @file{/usr} modified after February 1 of the
current year:

@c Idea from Rick Sladkey.
@example
touch -t 02010000 /tmp/stamp$$
find /usr -newer /tmp/stamp$$
rm -f /tmp/stamp$$
@end example

@deffn Test -anewer file
@deffnx Test -cnewer file
@deffnx Test -newer file
True if the file was last accessed (or its status changed, or it was
modified) more recently than @var{file} was modified.  These tests are
affected by @samp{-follow} only if @samp{-follow} comes before them on
the command line.  @xref{Symbolic Links}, for more information on
@samp{-follow}.  As an example, to list any files modified since
@file{/bin/sh} was last modified:

@example
find . -newer /bin/sh
@end example
@end deffn

@deffn Test -used n
True if the file was last accessed @var{n} days after its status was
last changed.  Useful for finding files that are not being used, and
could perhaps be archived or removed to save disk space.
@end deffn

@node Size
@section Size

@deffn Test -size n@r{[}bckwMG@r{]}
True if the file uses @var{n} units of space, rounding up.  The units
are 512-byte blocks by default, but they can be changed by adding a
one-character suffix to @var{n}:

@table @code
@item b
512-byte blocks (never 1024)
@item c
bytes
@item k
kilobytes (1024 bytes)
@item w
2-byte words
@item M
Megabytes
@item G
Gigabytes
@end table

The `b' suffix always considers blocks to be 512 bytes.  This is not
affected by the setting (or non-setting) of the POSIXLY_CORRECT
environment variable.  This behaviour is different to the behaviour of
the @samp{-ls} action).  If you want to use 1024-byte units, use the
`k' suffix instead.

The number can be prefixed with a `+' or a `-'.  A plus sign indicates
that the test should succeed if the file uses at least @var{n} units
of storage (this is the way I normally use this test) and a minus sign
indicates that the test should succeed if the file uses less than
@var{n} units of storage.   There is no `=' prefix, because that's the 
default anyway.  

The size does not count indirect blocks, but it does count blocks in
sparse files that are not actually allocated.  This handling of sparse
files differs from the output of the @samp{%k} and @samp{%b} format
specifiers for the @samp{-printf} predicate.

@end deffn

@deffn Test -empty
True if the file is empty and is either a regular file or a directory.
This might make it a good candidate for deletion.  This test is useful
with @samp{-depth} (@pxref{Directories}) and @samp{-exec rm -rf '@{@}' ';'}
(@pxref{Single File}).
@end deffn

@node Type
@section Type

@deffn Test -type c
True if the file is of type @var{c}:

@table @code
@item b
block (buffered) special
@item c
character (unbuffered) special
@item d
directory
@item p
named pipe (FIFO)
@item f
regular file
@item l
symbolic link
@item s
socket
@item D
door (Solaris)
@end table
@end deffn

@deffn Test -xtype c
The same as @samp{-type} unless the file is a symbolic link.  For
symbolic links: if @samp{-follow} has not been given, true if the file
is a link to a file of type @var{c}; if @samp{-follow} has been given,
true if @var{c} is @samp{l}.  In other words, for symbolic links,
@samp{-xtype} checks the type of the file that @samp{-type} does not
check.  @xref{Symbolic Links}, for more information on @samp{-follow}.
@end deffn

@node Owner
@section Owner

@deffn Test -user uname
@deffnx Test -group gname
True if the file is owned by user @var{uname} (belongs to group @var{gname}).
A numeric ID is allowed.
@end deffn

@deffn Test -uid n
@deffnx Test -gid n
True if the file's numeric user ID (group ID) is @var{n}.  These tests
support ranges (@samp{+@var{n}} and @samp{-@var{n}}), unlike
@samp{-user} and @samp{-group}.
@end deffn

@deffn Test -nouser
@deffnx Test -nogroup
True if no user corresponds to the file's numeric user ID (no group
corresponds to the numeric group ID).  These cases usually mean that the
files belonged to users who have since been removed from the system.
You probably should change the ownership of such files to an existing
user or group, using the @code{chown} or @code{chgrp} program.
@end deffn

@node Permissions
@section Permissions

@xref{File Permissions}, for information on how file permissions are
structured and how to specify them.

@deffn Test -perm mode
True if the
file's permissions are exactly @var{mode} (which can be numeric or symbolic).
Symbolic modes use mode 0 as a point of departure.
If @var{mode} starts with @samp{-}, true if
@emph{all} of the permissions set in @var{mode} are set for the file;
permissions not set in @var{mode} are ignored.
If @var{mode} starts with @samp{+}, true if
@emph{any} of the permissions set in @var{mode} are set for the file;
permissions not set in @var{mode} are ignored.
@end deffn

@node Contents
@section Contents

To search for files based on their contents, you can use the @code{grep}
program.  For example, to find out which C source files in the current
directory contain the string @samp{thing}, you can do:

@example
grep -l thing *.[ch]
@end example

If you also want to search for the string in files in subdirectories,
you can combine @code{grep} with @code{find} and @code{xargs}, like
this:

@example
find . -name '*.[ch]' | xargs grep -l thing
@end example

The @samp{-l} option causes @code{grep} to print only the names of files
that contain the string, rather than the lines that contain it.  The
string argument (@samp{thing}) is actually a regular expression, so it
can contain metacharacters.  This method can be refined a little by
using the @samp{-r} option to make @code{xargs} not run @code{grep} if
@code{find} produces no output, and using the @code{find} action
@samp{-print0} and the @code{xargs} option @samp{-0} to avoid
misinterpreting files whose names contain spaces:

@example
find . -name '*.[ch]' -print0 | xargs -r -0 grep -l thing
@end example

For a fuller treatment of finding files whose contents match a pattern,
see the manual page for @code{grep}.

@node Directories
@section Directories

Here is how to control which directories @code{find} searches, and how
it searches them.  These two options allow you to process a horizontal
slice of a directory tree.

@deffn Option -maxdepth levels
Descend at most @var{levels} (a non-negative integer) levels of
directories below the command line arguments.  @samp{-maxdepth 0} means
only apply the tests and actions to the command line arguments.
@end deffn

@deffn Option -mindepth levels
Do not apply any tests or actions at levels less than @var{levels} (a
non-negative integer).  @samp{-mindepth 1} means process all files
except the command line arguments.
@end deffn

@deffn Option -depth
Process each directory's contents before the directory itself.  Doing
this is a good idea when producing lists of files to archive with
@code{cpio} or @code{tar}.  If a directory does not have write
permission for its owner, its contents can still be restored from the
archive since the directory's permissions are restored after its contents.
@end deffn

@deffn Action -prune
If @samp{-depth} is not given, true; do not descend into the current
directory.  If @samp{-depth} is given, false; no effect.  @samp{-prune}
only affects tests and actions that come after it in the expression, not
those that come before.

For example, to skip the directory @file{src/emacs} and all files and
directories under it, and print the names of the other files found:

@example
find . -path './src/emacs' -prune -o -print
@end example
@end deffn

@deffn Option -noleaf
Do not optimize by assuming that directories contain 2 fewer
subdirectories than their hard link count.  This option is needed when
searching filesystems that do not follow the Unix directory-link
convention, such as CD-ROM or MS-DOS filesystems or AFS volume mount
points.  Each directory on a normal Unix filesystem has at least 2 hard
links: its name and its @file{.}  entry.  Additionally, its
subdirectories (if any) each have a @file{..}  entry linked to that
directory.  When @code{find} is examining a directory, after it has
statted 2 fewer subdirectories than the directory's link count, it knows
that the rest of the entries in the directory are non-directories
(@dfn{leaf} files in the directory tree).  If only the files' names need
to be examined, there is no need to stat them; this gives a significant
increase in search speed.
@end deffn

@deffn Option -ignore_readdir_race
If a file disappears after its name has been read from a directory but
before @code{find} gets around to examining the file with @code{stat},
don't issue an error message.  If you don't specify this option, an
error message will be issued.  This option can be useful in system
scripts (cron scripts, for example) that examine areas of the
filesystem that change frequently (mail queues, temporary directories,
and so forth), because this scenario is common for those sorts of
directories.  Completely silencing error messages from @code{find} is
undesirable, so this option neatly solves the problem.  There is no
way to search one part of the filesystem with this option on and part
of it with this option off, though.
@end deffn

@deffn Option -noignore_readdir_race
This option reverses the effect of the @samp{-ignore_readdir_race} option.
@end deffn


@node Filesystems
@section Filesystems

A @dfn{filesystem} is a section of a disk, either on the local host or
mounted from a remote host over a network.  Searching network
filesystems can be slow, so it is common to make @code{find} avoid them.

There are two ways to avoid searching certain filesystems.  One way is
to tell @code{find} to only search one filesystem:

@deffn Option -xdev
@deffnx Option -mount
Don't descend directories on other filesystems.  These options are synonyms.
@end deffn

The other way is to check the type of filesystem each file is on, and
not descend directories that are on undesirable filesystem types:

@deffn Test -fstype type
True if the file is on a filesystem of type @var{type}.  The valid
filesystem types vary among different versions of Unix; an incomplete
list of filesystem types that are accepted on some version of Unix or
another is:
@example
ufs 4.2 4.3 nfs tmp mfs S51K S52K
@end example
You can use @samp{-printf} with the @samp{%F} directive to see the types
of your filesystems.  @xref{Print File Information}.  @samp{-fstype} is
usually used with @samp{-prune} to avoid searching remote filesystems
(@pxref{Directories}). 
@end deffn

@node Combining Primaries With Operators
@section Combining Primaries With Operators

Operators build a complex expression from tests and actions.
The operators are, in order of decreasing precedence:

@table @code
@item @asis{( @var{expr} )}
@findex ()
Force precedence.  True if @var{expr} is true.

@item @asis{! @var{expr}}
@itemx @asis{-not @var{expr}}
@findex !
@findex -not
True if @var{expr} is false.

@item @asis{@var{expr1 expr2}}
@itemx @asis{@var{expr1} -a @var{expr2}}
@itemx @asis{@var{expr1} -and @var{expr2}}
@findex -a
@findex -and
And; @var{expr2} is not evaluated if @var{expr1} is false.

@item @asis{@var{expr1} -o @var{expr2}}
@itemx @asis{@var{expr1} -or @var{expr2}}
@findex -o
@findex -or
Or; @var{expr2} is not evaluated if @var{expr1} is true.

@item @asis{@var{expr1} , @var{expr2}}
@findex ,
List; both @var{expr1} and @var{expr2} are always evaluated.  True if
@var{expr2} is true.  The value of @var{expr1} is discarded.  This
operator lets you do multiple independent operations on one traversal,
without depending on whether other operations succeeded.
@end table

@code{find} searches the directory tree rooted at each file name by
evaluating the expression from left to right, according to the rules of
precedence, until the outcome is known (the left hand side is false for
@samp{-and}, true for @samp{-or}), at which point @code{find} moves on
to the next file name.

There are two other tests that can be useful in complex expressions:

@deffn Test -true
Always true.
@end deffn

@deffn Test -false
Always false.
@end deffn

@node Actions, Common Tasks, Finding Files, Top
@chapter Actions

There are several ways you can print information about the files that
match the criteria you gave in the @code{find} expression.  You can
print the information either to the standard output or to a file that
you name.  You can also execute commands that have the file names as
arguments.  You can use those commands as further filters to select files.

@menu
* Print File Name::
* Print File Information::
* Run Commands::
* Adding Tests::
@end menu

@node Print File Name
@section Print File Name

@deffn Action -print
True; print the full file name on the standard output, followed by a
newline.
@end deffn

@deffn Action -fprint file
True; print the full file name into file @var{file}, followed by a
newline.  If @var{file} does not exist when @code{find} is run, it is
created; if it does exist, it is truncated to 0 bytes.  The file names
@file{/dev/stdout} and @file{/dev/stderr} are handled specially; they
refer to the standard output and standard error output, respectively.
@end deffn

@node Print File Information
@section Print File Information

@deffn Action -ls
True; list the current file in @samp{ls -dils} format on the standard
output.  The output looks like this:

@smallexample
204744   17 -rw-r--r--   1 djm      staff       17337 Nov  2  1992 ./lwall-quotes
@end smallexample

The fields are:

@enumerate
@item
The inode number of the file.  @xref{Hard Links}, for how to find files
based on their inode number.

@item
the number of blocks in the file.  The block counts are of 1K blocks,
unless the environment variable @code{POSIXLY_CORRECT} is set, in which
case 512-byte blocks are used.  @xref{Size}, for how to find files based
on their size.

@item
The file's type and permissions.  The type is shown as a dash for a
regular file; for other file types, a letter like for @samp{-type} is
used (@pxref{Type}).  The permissions are read, write, and execute for
the file's owner, its group, and other users, respectively; a dash means
the permission is not granted.  @xref{File Permissions}, for more details
about file permissions.  @xref{Permissions}, for how to find files based
on their permissions.

@item
The number of hard links to the file.

@item
The user who owns the file.

@item
The file's group.

@item
The file's size in bytes.

@item
The date the file was last modified.

@item
The file's name.  @samp{-ls} quotes non-printable characters in the file
names using C-like backslash escapes.
@end enumerate
@end deffn

@deffn Action -fls file
True; like @samp{-ls} but write to @var{file} like @samp{-fprint}
(@pxref{Print File Name}).
@end deffn

@deffn Action -printf format
True; print @var{format} on the standard output, interpreting @samp{\}
escapes and @samp{%} directives.  Field widths and precisions can be
specified as with the @code{printf} C function.  Unlike @samp{-print},
@samp{-printf} does not add a newline at the end of the string.
@end deffn

@deffn Action -fprintf file format
True; like @samp{-printf} but write to @var{file} like @samp{-fprint}
(@pxref{Print File Name}).
@end deffn

@menu
* Escapes::
* Format Directives::
* Time Formats::
@end menu

@node Escapes
@subsection Escapes

The escapes that @samp{-printf} and @samp{-fprintf} recognize are:

@table @code
@item \a
Alarm bell.
@item \b
Backspace.
@item \c
Stop printing from this format immediately and flush the output.
@item \f
Form feed.
@item \n
Newline.
@item \r
Carriage return.
@item \t
Horizontal tab.
@item \v
Vertical tab.
@item \\
A literal backslash (@samp{\}).
@item \NNN
The character whose ASCII code is NNN (octal).
@end table

A @samp{\} character followed by any other character is treated as an
ordinary character, so they both are printed, and a warning message is
printed to the standard error output (because it was probably a typo).

@node Format Directives
@subsection Format Directives

@samp{-printf} and @samp{-fprintf} support the following format
directives to print information about the file being processed.
The C @code{printf} function, field width and precision specifiers
are supported, as applied to string (%s) types. I.E. you can specify
"minimum field width"."maximum field width" for each directive.

@samp{%%} is a literal percent sign.  A @samp{%} character followed by
an unrecognised character (i.e. not a known directive or printf field
width and precision specifier), is discarded (but the unrecognised character
is printed), and a warning message is printed to the standard error output
(because it was probably a typo).

@menu
* Name Directives::
* Ownership Directives::
* Size Directives::
* Location Directives::
* Time Directives::
@end menu

@node Name Directives
@subsubsection Name Directives

@table @code
@item %p
File's name.
@item %f
File's name with any leading directories removed (only the last element).
@item %h
Leading directories of file's name (all but the last element and the
slash before it).
@item %P
File's name with the name of the command line argument under which
it was found removed from the beginning.
@item %H
Command line argument under which file was found.
@end table

@node Ownership Directives
@subsubsection Ownership Directives

@table @code
@item %g
File's group name, or numeric group ID if the group has no name.
@item %G
File's numeric group ID.
@item %u
File's user name, or numeric user ID if the user has no name.
@item %U
File's numeric user ID.
@item %m
File's permissions (in octal).
@end table

@node Size Directives
@subsubsection Size Directives

@table @code
@item %k
Amount of disk space occupied by the file, measured in 1K blocks
(rounded up).  This can be less than the length of the file if 
it is a sparse file (that is, it has ``holes'').
@item %b
File's size in 512-byte blocks (rounded up).  This also can be less 
than the length of the file, if the file is sparse.
@item %s
File's size in bytes.
@end table

@node Location Directives
@subsubsection Location Directives

@table @code
@item %d
File's depth in the directory tree; files named on the command line
have a depth of 0.
@item %F
Type of the filesystem the file is on; this value can be used for
@samp{-fstype} (@pxref{Directories}).
@item %l
Object of symbolic link (empty string if file is not a symbolic link).
@item %i
File's inode number (in decimal).
@item %n
Number of hard links to file.
@end table

@node Time Directives
@subsubsection Time Directives

Some of these directives use the C @code{ctime} function.  Its output
depends on the current locale, but it typically looks like

@example
Wed Nov  2 00:42:36 1994
@end example

@table @code
@item %a
File's last access time in the format returned by the C @code{ctime} function.
@item %A@var{k}
File's last access time in the format specified by @var{k}
(@pxref{Time Formats}). 
@item %c
File's last status change time in the format returned by the C @code{ctime}
function.
@item %C@var{k}
File's last status change time in the format specified by @var{k}
(@pxref{Time Formats}).
@item %t
File's last modification time in the format returned by the C @code{ctime}
function.
@item %T@var{k}
File's last modification time in the format specified by @var{k} 
(@pxref{Time Formats}). 
@end table

@node Time Formats
@subsection Time Formats

Below are the formats for the directives @samp{%A}, @samp{%C}, and
@samp{%T}, which print the file's timestamps.  Some of these formats
might not be available on all systems, due to differences in the C
@code{strftime} function between systems.

@menu
* Time Components::
* Date Components::
* Combined Time Formats::
@end menu

@node Time Components
@subsubsection Time Components

The following format directives print single components of the time.

@table @code
@item H
hour (00..23)
@item I
hour (01..12)
@item k
hour ( 0..23)
@item l
hour ( 1..12)
@item p
locale's AM or PM
@item Z
time zone (e.g., EDT), or nothing if no time zone is determinable
@item M
minute (00..59)
@item S
second (00..61)
@item @@
seconds since Jan. 1, 1970, 00:00 GMT.
@end table

@node Date Components
@subsubsection Date Components

The following format directives print single components of the date.

@table @code
@item a
locale's abbreviated weekday name (Sun..Sat)
@item A
locale's full weekday name, variable length (Sunday..Saturday)
@item b
@itemx h
locale's abbreviated month name (Jan..Dec)
@item B
locale's full month name, variable length (January..December)
@item m
month (01..12)
@item d
day of month (01..31)
@item w
day of week (0..6)
@item j
day of year (001..366)
@item U
week number of year with Sunday as first day of week (00..53)
@item W
week number of year with Monday as first day of week (00..53)
@item Y
year (1970@dots{})
@item y
last two digits of year (00..99)
@end table

@node Combined Time Formats
@subsubsection Combined Time Formats

The following format directives print combinations of time and date
components. 

@table @code
@item r
time, 12-hour (hh:mm:ss [AP]M)
@item T
time, 24-hour (hh:mm:ss)
@item X
locale's time representation (H:M:S)
@item c
locale's date and time (Sat Nov 04 12:02:33 EST 1989)
@item D
date (mm/dd/yy)
@item x
locale's date representation (mm/dd/yy)
@end table

@node Run Commands
@section Run Commands

You can use the list of file names created by @code{find} or
@code{locate} as arguments to other commands.  In this way you can
perform arbitrary actions on the files.

@menu
* Single File::
* Multiple Files::
* Querying::
@end menu

@node Single File
@subsection Single File

Here is how to run a command on one file at a time.

@deffn Action -exec command ;
Execute @var{command}; true if 0 status is returned.  @code{find} takes
all arguments after @samp{-exec} to be part of the command until an
argument consisting of @samp{;} is reached.  It replaces the string
@samp{@{@}} by the current file name being processed everywhere it
occurs in the command.  Both of these constructions need to be escaped
(with a @samp{\}) or quoted to protect them from expansion by the shell.
The command is executed in the directory in which @code{find} was run.

For example, to compare each C header file in the current directory with
the file @file{/tmp/master}:

@example
find . -name '*.h' -exec diff -u '@{@}' /tmp/master ';'
@end example
@end deffn

@node Multiple Files
@subsection Multiple Files

Sometimes you need to process files alone.  But when you
don't, it is faster to run a command on as many files as possible at a
time, rather than once per file.  Doing this saves on the time it takes
to start up the command each time.

To run a command on more than one file at once, use the @code{xargs}
command, which is invoked like this:

@example
xargs @r{[}@var{option}@dots{}@r{]} @r{[}@var{command} @r{[}@var{initial-arguments}@r{]}@r{]}
@end example

@code{xargs} reads arguments from the standard input, delimited by
blanks (which can be protected with double or single quotes or a
backslash) or newlines.  It executes the @var{command} (default is
@file{/bin/echo}) one or more times with any @var{initial-arguments}
followed by arguments read from standard input.  Blank lines on the
standard input are ignored.

Instead of blank-delimited names, it is safer to use @samp{find -print0}
or @samp{find -fprint0} and process the output by giving the @samp{-0}
or @samp{--null} option to GNU @code{xargs}, GNU @code{tar}, GNU
@code{cpio}, or @code{perl}.

You can use shell command substitution (backquotes) to process a list of
arguments, like this:

@example
grep -l sprintf `find $HOME -name '*.c' -print`
@end example

However, that method produces an error if the length of the @samp{.c}
file names exceeds the operating system's command-line length limit.
@code{xargs} avoids that problem by running the command as many times as
necessary without exceeding the limit:

@example
find $HOME -name '*.c' -print | xargs grep -l sprintf
@end example

However, if the command needs to have its standard input be a terminal
(@code{less}, for example), you have to use the shell command
substitution method.

The @code{xargs} command will process all its input, building command
lines and executing them, unless one of the commands exits with a
status of 255 (this will cause xargs to issue an error message and
stop) or it reads a line contains the end of file string specified
with the @samp{--eof} option. 

@menu
* Unsafe File Name Handling::
* Safe File Name Handling::
* Limiting Command Size::
* Interspersing File Names::
@end menu

@node Unsafe File Name Handling
@subsubsection Unsafe File Name Handling

Because file names can contain quotes, backslashes, blank characters,
and even newlines, it is not safe to process them using @code{xargs} in its
default mode of operation.  But since most files' names do not contain
blanks, this problem occurs only infrequently.  If you are only
searching through files that you know have safe names, then you need not
be concerned about it.

@c This example is adapted from:
@c From: pfalstad@stone.Princeton.EDU (Paul John Falstad)
@c Newsgroups: comp.unix.shell
@c Subject: Re: Beware xargs security holes
@c Date: 16 Oct 90 19:12:06 GMT
@c 
In many applications, if @code{xargs} botches processing a file because
its name contains special characters, some data might be lost.  The
importance of this problem depends on the importance of the data and
whether anyone notices the loss soon enough to correct it.  However,
here is an extreme example of the problems that using blank-delimited
names can cause.  If the following command is run daily from
@code{cron}, then any user can remove any file on the system:

@example
find / -name '#*' -atime +7 -print | xargs rm
@end example

For example, you could do something like this:

@example
eg$ echo > '#
vmunix'
@end example

@noindent
and then @code{cron} would delete @file{/vmunix}, if it ran
@code{xargs} with @file{/} as its current directory.

To delete other files, for example @file{/u/joeuser/.plan}, you could do
this:

@example
eg$ mkdir '#
'
eg$ cd '#
'
eg$ mkdir u u/joeuser u/joeuser/.plan'
'
eg$ echo > u/joeuser/.plan'
/#foo'
eg$ cd ..
eg$ find . -name '#*' -print | xargs echo
./# ./# /u/joeuser/.plan /#foo
@end example

@node Safe File Name Handling
@subsubsection Safe File Name Handling

Here is how to make @code{find} output file names so that they can be
used by other programs without being mangled or misinterpreted.  You can
process file names generated this way by giving the @samp{-0} or
@samp{--null} option to GNU @code{xargs}, GNU @code{tar}, GNU
@code{cpio}, or @code{perl}.

@deffn Action -print0
True; print the full file name on the standard output, followed by a
null character.
@end deffn

@deffn Action -fprint0 file
True; like @samp{-print0} but write to @var{file} like @samp{-fprint}
(@pxref{Print File Name}).
@end deffn

@node Limiting Command Size
@subsubsection Limiting Command Size

@code{xargs} gives you control over how many arguments it passes to the
command each time it executes it.  By default, it uses up to
@code{ARG_MAX} - 2k, or 20k, whichever is smaller, characters per
command.  It uses as many lines and arguments as fit within that limit.
The following options modify those values.

@table @code
@item --no-run-if-empty
@itemx -r
If the standard input does not contain any nonblanks, do not run the
command.  By default, the command is run once even if there is no input.

@item --max-lines@r{[}=@var{max-lines}@r{]}
@itemx -l@r{[}@var{max-lines}@r{]}
Use at most @var{max-lines} nonblank input lines per command line;
@var{max-lines} defaults to 1 if omitted.  Trailing blanks cause an
input line to be logically continued on the next input line, for the
purpose of counting the lines.  Implies @samp{-x}.

@item --max-args=@var{max-args}
@itemx -n @var{max-args}
Use at most @var{max-args} arguments per command line.  Fewer than
@var{max-args} arguments will be used if the size (see the @samp{-s}
option) is exceeded, unless the @samp{-x} option is given, in which case
@code{xargs} will exit.

@item --max-chars=@var{max-chars}
@itemx -s @var{max-chars}
Use at most @var{max-chars} characters per command line, including the
command and initial arguments and the terminating nulls at the ends of
the argument strings.

@item --max-procs=@var{max-procs}
@itemx -P @var{max-procs}
Run up to @var{max-procs} processes at a time; the default is 1.  If
@var{max-procs} is 0, @code{xargs} will run as many processes as
possible at a time.  Use the @samp{-n}, @samp{-s}, or @samp{-l} option
with @samp{-P}; otherwise chances are that the command will be run only
once.
@end table

@node Interspersing File Names
@subsubsection Interspersing File Names

@code{xargs} can insert the name of the file it is processing between
arguments you give for the command.  Unless you also give options to
limit the command size (@pxref{Limiting Command Size}), this mode of
operation is equivalent to @samp{find -exec} (@pxref{Single File}).

@table @code
@item --replace@r{[}=@var{replace-str}@r{]}
@itemx -i@r{[}@var{replace-str}@r{]}
Replace occurrences of @var{replace-str} in the initial arguments with
names read from standard input.  Also, unquoted blanks do not terminate
arguments.  If @var{replace-str} is omitted, it defaults to @samp{@{@}}
(like for @samp{find -exec}).  Implies @samp{-x} and @samp{-l 1}.  As an
example, to sort each file the @file{bills} directory, leaving the
output in that file name with @file{.sorted} appended, you could do:

@example
find bills -type f | xargs -iXX sort -o XX.sorted XX
@end example

@noindent
The equivalent command using @samp{find -exec} is:

@example
find bills -type f -exec sort -o '@{@}.sorted' '@{@}' ';'
@end example
@end table

@node Querying
@subsection Querying

To ask the user whether to execute a command on a single file, you can
use the @code{find} primary @samp{-ok} instead of @samp{-exec}:

@deffn Action -ok command ;
Like @samp{-exec} (@pxref{Single File}), but ask the user first (on
the standard input); if the response does not start with @samp{y} or
@samp{Y}, do not run the command, and return false.
@end deffn

When processing multiple files with a single command, to query the user
you give @code{xargs} the following option.  When using this option, you
might find it useful to control the number of files processed per
invocation of the command (@pxref{Limiting Command Size}).

@table @code
@item --interactive
@itemx -p
Prompt the user about whether to run each command line and read a line
from the terminal.  Only run the command line if the response starts
with @samp{y} or @samp{Y}.  Implies @samp{-t}.
@end table

@node Adding Tests
@section Adding Tests

You can test for file attributes that none of the @code{find} builtin
tests check.  To do this, use @code{xargs} to run a program that filters
a list of files printed by @code{find}.  If possible, use @code{find}
builtin tests to pare down the list, so the program run by @code{xargs}
has less work to do.  The tests builtin to @code{find} will likely run
faster than tests that other programs perform.

For example, here is a way to print the names of all of the unstripped
binaries in the @file{/usr/local} directory tree.  Builtin tests avoid
running @code{file} on files that are not regular files or are not
executable.

@example
find /usr/local -type f -perm +a=x | xargs file | 
  grep 'not stripped' | cut -d: -f1
@end example

@noindent
The @code{cut} program removes everything after the file name from the
output of @code{file}.

@c Idea from Martin Weitzel.
If you want to place a special test somewhere in the middle of a
@code{find} expression, you can use @samp{-exec} to run a program that
performs the test.  Because @samp{-exec} evaluates to the exit status of
the executed program, you can write a program (which can be a shell
script) that tests for a special attribute and make it exit with a true
(zero) or false (non-zero) status.  It is a good idea to place such a
special test @emph{after} the builtin tests, because it starts a new
process which could be avoided if a builtin test evaluates to false.
Use this method only when @code{xargs} is not flexible enough, because
starting one or more new processes to test each file is slower than
using @code{xargs} to start one process that tests many files.

Here is a shell script called @code{unstripped} that checks whether its
argument is an unstripped binary file:

@example
#! /bin/sh
file $1 | grep 'not stripped' > /dev/null
@end example

This script relies on the fact that the shell exits with the status of
the last program it executed, in this case @code{grep}.  @code{grep}
exits with a true status if it found any matches, false if not.  Here is
an example of using the script (assuming it is in your search path).  It
lists the stripped executables in the file @file{sbins} and the
unstripped ones in @file{ubins}.

@example
find /usr/local -type f -perm +a=x \
  \( -exec unstripped '@{@}' \; -fprint ubins -o -fprint sbins \)
@end example

@node Common Tasks, Databases, Actions, Top
@chapter Common Tasks

The sections that follow contain some extended examples that both give a
good idea of the power of these programs, and show you how to solve
common real-world problems.

@menu
* Viewing And Editing::
* Archiving::
* Cleaning Up::
* Strange File Names::
* Fixing Permissions::
* Classifying Files::
@end menu

@node Viewing And Editing
@section Viewing And Editing

To view a list of files that meet certain criteria, simply run your file
viewing program with the file names as arguments.  Shells substitute a
command enclosed in backquotes with its output, so the whole command
looks like this:

@example
less `find /usr/include -name '*.h' | xargs grep -l mode_t`
@end example

@noindent
You can edit those files by giving an editor name instead of a file
viewing program.

@node Archiving
@section Archiving

You can pass a list of files produced by @code{find} to a file archiving
program.  GNU @code{tar} and @code{cpio} can both read lists of file
names from the standard input---either delimited by nulls (the safe way)
or by blanks (the lazy, risky default way).  To use null-delimited
names, give them the @samp{--null} option.  You can store a file archive
in a file, write it on a tape, or send it over a network to extract on
another machine.

One common use of @code{find} to archive files is to send a list of the
files in a directory tree to @code{cpio}.  Use @samp{-depth} so if a
directory does not have write permission for its owner, its contents can
still be restored from the archive since the directory's permissions are
restored after its contents.  Here is an example of doing this using
@code{cpio}; you could use a more complex @code{find} expression to
archive only certain files.

@example
find . -depth -print0 |
  cpio --create --null --format=crc --file=/dev/nrst0
@end example

You could restore that archive using this command:

@example
cpio --extract --null --make-dir --unconditional \
  --preserve --file=/dev/nrst0
@end example

Here are the commands to do the same things using @code{tar}:

@example
find . -depth -print0 |
  tar --create --null --files-from=- --file=/dev/nrst0

tar --extract --null --preserve-perm --same-owner \
  --file=/dev/nrst0
@end example

@c Idea from Rick Sladkey.
Here is an example of copying a directory from one machine to another:

@example
find . -depth -print0 | cpio -0o -Hnewc |
  rsh @var{other-machine} "cd `pwd` && cpio -i0dum"
@end example

@node Cleaning Up
@section Cleaning Up

@c Idea from Jim Meyering.
This section gives examples of removing unwanted files in various situations.
Here is a command to remove the CVS backup files created when an update
requires a merge:

@example
find . -name '.#*' -print0 | xargs -0r rm -f
@end example

@c Idea from Franc,ois Pinard.
You can run this command to clean out your clutter in @file{/tmp}.  You
might place it in the file your shell runs when you log out
(@file{.bash_logout}, @file{.logout}, or @file{.zlogout}, depending on
which shell you use).

@example
find /tmp -user $LOGNAME -type f -print0 | xargs -0 -r rm -f
@end example

If your @code{find} command removes directories, you may find that 
you get a spurious error message when @code{find} tries to recurse
into a directory that has now been removed.  Using the @samp{-depth}
option will normally resolve this problem.

@c Idea from Noah Friedman.
To remove old Emacs backup and auto-save files, you can use a command
like the following.  It is especially important in this case to use
null-terminated file names because Emacs packages like the VM mailer
often create temporary file names with spaces in them, like @file{#reply
to David J. MacKenzie<1>#}.

@example
find ~ \( -name '*~' -o -name '#*#' \) -print0 |
  xargs --no-run-if-empty --null rm -vf
@end example

Removing old files from @file{/tmp} is commonly done from @code{cron}:

@c Idea from Kaveh Ghazi.
@example
find /tmp /var/tmp -not -type d -mtime +3 -print0 |
  xargs --null --no-run-if-empty rm -f

find /tmp /var/tmp -depth -mindepth 1 -type d -empty -exec rmdir @{@} \;
@end example

The second @code{find} command above uses @samp{-depth} so it cleans out
empty directories depth-first, hoping that the parents become empty and
can be removed too.  It uses @samp{-mindepth} to avoid removing
@file{/tmp} itself if it becomes totally empty.

@node Strange File Names
@section Strange File Names

@c Idea from:
@c From: tmatimar@isgtec.com (Ted Timar)
@c Newsgroups: comp.unix.questions,comp.unix.shell,comp.answers,news.answers
@c Subject: Unix - Frequently Asked Questions (2/7) [Frequent posting]
@c Subject: How do I remove a file with funny characters in the filename ?
@c Date: Thu Mar 18 17:16:55 EST 1993
@code{find} can help you remove or rename a file with strange characters
in its name.  People are sometimes stymied by files whose names contain
characters such as spaces, tabs, control characters, or characters with
the high bit set.  The simplest way to remove such files is:

@example
rm -i @var{some*pattern*that*matches*the*problem*file}
@end example

@code{rm} asks you whether to remove each file matching the given
pattern.  If you are using an old shell, this approach might not work if
the file name contains a character with the high bit set; the shell may
strip it off.  A more reliable way is:

@example
find . -maxdepth 1 @var{tests} -ok rm '@{@}' \;
@end example

@noindent
where @var{tests} uniquely identify the file.  The @samp{-maxdepth 1}
option prevents @code{find} from wasting time searching for the file in
any subdirectories; if there are no subdirectories, you may omit it.  A
good way to uniquely identify the problem file is to figure out its
inode number; use

@example
ls -i
@end example

Suppose you have a file whose name contains control characters, and you
have found that its inode number is 12345.  This command prompts you for
whether to remove it:

@example
find . -maxdepth 1 -inum 12345 -ok rm -f '@{@}' \;
@end example

If you don't want to be asked, perhaps because the file name may contain
a strange character sequence that will mess up your screen when printed,
then use @samp{-exec} instead of @samp{-ok}.

If you want to rename the file instead, you can use @code{mv} instead of
@code{rm}:

@example
find . -maxdepth 1 -inum 12345 -ok mv '@{@}' @var{new-file-name} \;
@end example

@node Fixing Permissions
@section Fixing Permissions

Suppose you want to make sure that everyone can write to the directories in a
certain directory tree.  Here is a way to find directories lacking either
user or group write permission (or both), and fix their permissions:

@example
find . -type d -not -perm -ug=w | xargs chmod ug+w
@end example

@noindent
You could also reverse the operations, if you want to make sure that
directories do @emph{not} have world write permission.

@node Classifying Files
@section Classifying Files

@c Idea from:
@c From: martin@mwtech.UUCP (Martin Weitzel)
@c Newsgroups: comp.unix.wizards,comp.unix.questions
@c Subject: Advanced usage of 'find' (Re: Unix security automating script)
@c Date: 22 Mar 90 15:05:19 GMT
If you want to classify a set of files into several groups based on
different criteria, you can use the comma operator to perform multiple
independent tests on the files.  Here is an example:

@example
find / -type d \( -perm -o=w -fprint allwrite , \
  -perm -o=x -fprint allexec \)

echo "Directories that can be written to by everyone:"
cat allwrite
echo ""
echo "Directories with search permissions for everyone:"
cat allexec
@end example

@code{find} has only to make one scan through the directory tree (which
is one of the most time consuming parts of its work).

@node Databases, File Permissions, Common Tasks, Top
@chapter File Name Databases

The file name databases used by @code{locate} contain lists of files
that were in particular directory trees when the databases were last
updated.  The file name of the default database is determined when
@code{locate} and @code{updatedb} are configured and installed.  The
frequency with which the databases are updated and the directories for
which they contain entries depend on how often @code{updatedb} is run,
and with which arguments.

@menu
* Database Locations::
* Database Formats::
@end menu

@node Database Locations
@section Database Locations

There can be multiple file name databases.  Users can select which
databases @code{locate} searches using an environment variable or a
command line option.  The system administrator can choose the file name
of the default database, the frequency with which the databases are
updated, and the directories for which they contain entries.  File name
databases are updated by running the @code{updatedb} program, typically
nightly.

In networked environments, it often makes sense to build a database at
the root of each filesystem, containing the entries for that filesystem.
@code{updatedb} is then run for each filesystem on the fileserver where
that filesystem is on a local disk, to prevent thrashing the network.
Here are the options to @code{updatedb} to select which directories each
database contains entries for:

@table @code
@item --localpaths='@var{path}@dots{}'
Non-network directories to put in the database.
Default is @file{/}.

@item --netpaths='@var{path}@dots{}'
Network (NFS, AFS, RFS, etc.) directories to put in the database.
The environment variable @code{NETPATHS} also sets this value.
Default is none.


@item --prunepaths='@var{path}@dots{}'
Directories to not put in the database, which would otherwise be.
The environment variable @code{PRUNEPATHS} also sets this value.
Default is @file{/tmp /usr/tmp /var/tmp /afs}.

@item --prunefs='@var{path}@dots{}'
File systems to not put in the database, which would otherwise be.
Note that files are pruned when a file system is reached;
Any file system mounted under an undesired file system will be
ignored.
The environment variable @code{PRUNEFS} also sets this value.
Default is @file{nfs NFS proc}.

@item --output=@var{dbfile}
The database file to build.
Default is system-dependent, but typically @file{/usr/local/var/locatedb}.

@item --localuser=@var{user}
The user to search the non-network directories as, using @code{su}.
Default is to search the non-network directories as the current user.
You can also use the environment variable @code{LOCALUSER} to set this user.

@item --netuser=@var{user}
The user to search network directories as, using @code{su}.
Default is @code{daemon}.
You can also use the environment variable @code{NETUSER} to set this user.
@end table

@node Database Formats
@section Database Formats

The file name databases contain lists of files that were in particular
directory trees when the databases were last updated.  The file name
database format changed starting with GNU @code{locate} version 4.0 to
allow machines with different byte orderings to share the databases.  The
new GNU @code{locate} can read both the old and new database formats.
However, old versions of @code{locate} and @code{find} produce incorrect
results if given a new-format database.

@menu
* New Database Format::
* Sample Database::
* Old Database Format::
@end menu

@node New Database Format
@subsection New Database Format

@code{updatedb} runs a program called @code{frcode} to
@dfn{front-compress} the list of file names, which reduces the database
size by a factor of 4 to 5.  Front-compression (also known as
incremental encoding) works as follows.

The database entries are a sorted list (case-insensitively, for users'
convenience).  Since the list is sorted, each entry is likely to share a
prefix (initial string) with the previous entry.  Each database entry
begins with an offset-differential count byte, which is the additional
number of characters of prefix of the preceding entry to use beyond the
number that the preceding entry is using of its predecessor.  (The
counts can be negative.)  Following the count is a null-terminated ASCII
remainder---the part of the name that follows the shared prefix.

If the offset-differential count is larger than can be stored in a byte
(+/-127), the byte has the value 0x80 and the count follows in a 2-byte
word, with the high byte first (network byte order).

Every database begins with a dummy entry for a file called
@file{LOCATE02}, which @code{locate} checks for to ensure that the
database file has the correct format; it ignores the entry in doing the
search.

Databases can not be concatenated together, even if the first (dummy)
entry is trimmed from all but the first database.  This is because the
offset-differential count in the first entry of the second and following
databases will be wrong.

@node Sample Database
@subsection Sample Database

Sample input to @code{frcode}:
@c with nulls changed to newlines:

@example
/usr/src
/usr/src/cmd/aardvark.c
/usr/src/cmd/armadillo.c
/usr/tmp/zoo
@end example

Length of the longest prefix of the preceding entry to share:

@example
0 /usr/src
8 /cmd/aardvark.c
14 rmadillo.c
5 tmp/zoo
@end example

Output from @code{frcode}, with trailing nulls changed to newlines
and count bytes made printable:

@example
0 LOCATE02
0 /usr/src
8 /cmd/aardvark.c
6 rmadillo.c
-9 tmp/zoo
@end example

(6 = 14 - 8, and -9 = 5 - 14)

@node Old Database Format
@subsection Old Database Format

The old database format is used by Unix @code{locate} and @code{find}
programs and earlier releases of the GNU ones.  @code{updatedb} produces
this format if given the @samp{--old-format} option.

@code{updatedb} runs programs called @code{bigram} and @code{code} to
produce old-format databases.  The old format differs from the new one
in the following ways.  Instead of each entry starting with an
offset-differential count byte and ending with a null, byte values from
0 through 28 indicate offset-differential counts from -14 through 14.
The byte value indicating that a long offset-differential count follows
is 0x1e (30), not 0x80.  The long counts are stored in host byte order,
which is not necessarily network byte order, and host integer word size,
which is usually 4 bytes.  They also represent a count 14 less than
their value.  The database lines have no termination byte; the start of
the next line is indicated by its first byte having a value <= 30.

In addition, instead of starting with a dummy entry, the old database
format starts with a 256 byte table containing the 128 most common
bigrams in the file list.  A bigram is a pair of adjacent bytes.  Bytes
in the database that have the high bit set are indexes (with the high
bit cleared) into the bigram table.  The bigram and offset-differential
count coding makes these databases 20-25% smaller than the new format,
but makes them not 8-bit clean.  Any byte in a file name that is in the
ranges used for the special codes is replaced in the database by a
question mark, which not coincidentally is the shell wildcard to match a
single character.

The old format therefore can not faithfully store entries with non-ASCII
characters. It therefore should not be used in internationalized
environments.

@node File Permissions, Reference, Databases, Top
@chapter File Permissions

@include perm.texi

@node Reference, Primary Index, File Permissions, Top
@chapter Reference

Below are summaries of the command line syntax for the programs
discussed in this manual.

@menu
* Invoking find::
* Invoking locate::
* Invoking updatedb::
* Invoking xargs::
@end menu

@node Invoking find, Invoking locate, , Reference
@section Invoking @code{find}

@example
find @r{[}@var{file}@dots{}@r{]} @r{[}@var{expression}@r{]}
@end example

@code{find} searches the directory tree rooted at each file name
@var{file} by evaluating the @var{expression} on each file it finds in
the tree.

@code{find} considers the first argument that begins with @samp{-},
@samp{(}, @samp{)}, @samp{,}, or @samp{!} to be the beginning of the
expression; any arguments before it are paths to search, and any
arguments after it are the rest of the expression.  If no paths are
given, the current directory is used.  If no expression is given, the
expression @samp{-print} is used.

@code{find} exits with status 0 if all files are processed successfully,
greater than 0 if errors occur.

@xref{Primary Index}, for a summary of all of the tests, actions, and
options that the expression can contain.

@code{find} also recognizes two options for administrative use:

@table @code
@item --help
Print a summary of the command-line argument format and exit.
@item --version
Print the version number of @code{find} and exit.
@end table

@node Invoking locate, Invoking updatedb, Invoking find, Reference
@section Invoking @code{locate}

@example
locate @r{[}@var{option}@dots{}@r{]} @var{pattern}@dots{}
@end example

@table @code
@item --database=@var{path}
@itemx -d @var{path}
Instead of searching the default file name database, search the file
name databases in @var{path}, which is a colon-separated list of
database file names.  You can also use the environment variable
@code{LOCATE_PATH} to set the list of database files to search.  The
option overrides the environment variable if both are used.

@item --existing
@itemx -e
Only print out such names which currently exist (instead of such names
which existed when the database was created).
Note that this may slow down the program a lot, if there are many matches
in the database.

@item --ignore-case
@itemx -i
Ignore case distinctions in both the pattern and the file names.

@item --help
Print a summary of the options to @code{locate} and exit.

@item --version
Print the version number of @code{locate} and exit.
@end table

@node Invoking updatedb, Invoking xargs, Invoking locate, Reference
@section Invoking @code{updatedb}

@example
updatedb @r{[}@var{option}@dots{}@r{]}
@end example

@table @code
@item --localpaths='@var{path}@dots{}'
Non-network directories to put in the database.
Default is @file{/}.

@item --netpaths='@var{path}@dots{}'
Network (NFS, AFS, RFS, etc.) directories to put in the database.
The environment variable @code{NETPATHS} also sets this value.
Default is none.

@item --prunepaths='@var{path}@dots{}'
Directories to not put in the database, which would otherwise be.
The environment variable @code{PRUNEPATHS} also sets this value.
Default is @file{/tmp /usr/tmp /var/tmp /afs}.

@item --prunefs='@var{path}@dots{}'
File systems to not put in the database, which would otherwise be.
Note that files are pruned when a file system is reached;
Any file system mounted under an undesired file system will be
ignored.
The environment variable @code{PRUNEFS} also sets this value.
Default is @file{nfs NFS proc}.

@item --output=@var{dbfile}
The database file to build.
Default is system-dependent, but typically @file{/usr/local/var/locatedb}.

@item --localuser=@var{user}
The user to search the non-network directories as, using @code{su}.
Default is to search the non-network directories as the current user.
You can also use the environment variable @code{LOCALUSER} to set this user.

@item --netuser=@var{user}
The user to search network directories as, using @code{su}(1).
Default is @code{daemon}.
You can also use the environment variable @code{NETUSER} to set this user.
@end table

@node Invoking xargs, ,  Invoking updatedb, Reference
@section Invoking @code{xargs}

@example
xargs @r{[}@var{option}@dots{}@r{]} @r{[}@var{command} @r{[}@var{initial-arguments}@r{]}@r{]}
@end example

@code{xargs} exits with the following status:

@table @asis
@item 0
if it succeeds
@item 123
if any invocation of the command exited with status 1-125
@item 124
if the command exited with status 255
@item 125
if the command is killed by a signal
@item 126
if the command cannot be run
@item 127
if the command is not found
@item 1
if some other error occurred.
@end table

@table @code
@item --null
@itemx -0
Input filenames are terminated by a null character instead of by
whitespace, and the quotes and backslash are not special (every
character is taken literally).  Disables the end of file string, which
is treated like any other argument.

@item --eof@r{[}=@var{eof-str}@r{]}
@itemx -e@r{[}@var{eof-str}@r{]}
Set the end of file string to @var{eof-str}.  If the end of file string
occurs as a line of input, the rest of the input is ignored.  If
@var{eof-str} is omitted, there is no end of file string.  If this
option is not given, the end of file string defaults to @samp{_}.

@item --help
Print a summary of the options to @code{xargs} and exit.

@item --replace@r{[}=@var{replace-str}@r{]}
@itemx -i@r{[}@var{replace-str}@r{]}
Replace occurrences of @var{replace-str} in the initial arguments with
names read from standard input.  Also, unquoted blanks do not terminate
arguments.  If @var{replace-str} is omitted, it defaults to @samp{@{@}}
(like for @samp{find -exec}).  Implies @samp{-x} and @samp{-l 1}.

@item --max-lines@r{[}=@var{max-lines}@r{]}
@itemx -l@r{[}@var{max-lines}@r{]}
Use at most @var{max-lines} nonblank input lines per command line;
@var{max-lines} defaults to 1 if omitted.  Trailing blanks cause an
input line to be logically continued on the next input line, for the
purpose of counting the lines.  Implies @samp{-x}.

@item --max-args=@var{max-args}
@itemx -n @var{max-args}
Use at most @var{max-args} arguments per command line.  Fewer than
@var{max-args} arguments will be used if the size (see the @samp{-s}
option) is exceeded, unless the @samp{-x} option is given, in which case
@code{xargs} will exit.

@item --interactive
@itemx -p
Prompt the user about whether to run each command line and read a line
from the terminal.  Only run the command line if the response starts
with @samp{y} or @samp{Y}.  Implies @samp{-t}.

@item --no-run-if-empty
@itemx -r
If the standard input does not contain any nonblanks, do not run the
command.  By default, the command is run once even if there is no input.

@item --max-chars=@var{max-chars}
@itemx -s @var{max-chars}
Use at most @var{max-chars} characters per command line, including the
command and initial arguments and the terminating nulls at the ends of
the argument strings.

@item --verbose
@itemx -t
Print the command line on the standard error output before executing
it.

@item --version
Print the version number of @code{xargs} and exit.

@item --exit
@itemx -x
Exit if the size (see the @samp{-s} option) is exceeded.


@item --max-procs=@var{max-procs}
@itemx -P @var{max-procs}
Run up to @var{max-procs} processes at a time; the default is 1.  If
@var{max-procs} is 0, @code{xargs} will run as many processes as
possible at a time.
@end table

@node Primary Index, , Reference, Top
@unnumbered @code{find} Primary Index

This is a list of all of the primaries (tests, actions, and options)
that make up @code{find} expressions for selecting files.  @xref{find
Expressions}, for more information on expressions.

@printindex fn

@contents
@bye

@comment texi related words used by Emacs' spell checker ispell.el

@comment LocalWords: texinfo setfilename settitle setchapternewpage
@comment LocalWords: iftex finalout ifinfo DIR titlepage vskip pt
@comment LocalWords: filll dir samp dfn noindent xref pxref
@comment LocalWords: var deffn texi deffnx itemx emph asis
@comment LocalWords: findex smallexample subsubsection cindex

@comment other words used by Emacs' spell checker ispell.el
@comment LocalWords: README fred updatedb xargs Plett Rendell akefile
@comment LocalWords: args grep Filesystems fo foo fOo wildcards iname
@comment LocalWords: ipath regex iregex expr fubar regexps
@comment LocalWords: metacharacters macs sr sc inode lname ilname
@comment LocalWords: sysdep noleaf ls inum xdev filesystems usr atime
@comment LocalWords: ctime mtime amin cmin mmin al daystart Sladkey rm
@comment LocalWords: anewer cnewer bckw rf xtype uname gname uid gid
@comment LocalWords: nouser nogroup chown chgrp perm ch maxdepth
@comment LocalWords: mindepth cpio src CD AFS statted stat fstype ufs
@comment LocalWords: nfs tmp mfs printf fprint dils rw djm Nov lwall
@comment LocalWords: POSIXLY fls fprintf strftime locale's EDT GMT AP
@comment LocalWords: EST diff perl backquotes sprintf Falstad Oct cron
@comment LocalWords: eg vmunix mkdir afs allexec allwrite ARG bigram
@comment LocalWords: bigrams cd chmod comp crc CVS dbfile dum eof
@comment LocalWords: fileserver filesystem fn frcode Ghazi Hnewc iXX
@comment LocalWords: joeuser Kaveh localpaths localuser LOGNAME
@comment LocalWords: Meyering mv netpaths netuser nonblank nonblanks
@comment LocalWords: ois ok Pinard printindex proc procs prunefs
@comment LocalWords: prunepaths pwd RFS rmadillo rmdir rsh sbins str
@comment LocalWords: su Timar ubins ug unstripped vf VM Weitzel
@comment LocalWords: wildcard zlogout