Lib/commands.py

   1 """Execute shell commands via os.popen() and return status, output.
   2
   3 Interface summary:
   4
   5        import commands
   6
   7        outtext = commands.getoutput(cmd)
   8        (exitstatus, outtext) = commands.getstatusoutput(cmd)
   9        outtext = commands.getstatus(file)  # returns output of "ls -ld file"
  10
  11 A trailing newline is removed from the output string.
  12
  13 Encapsulates the basic operation:
  14
  15       pipe = os.popen('{ ' + cmd + '; } 2>&1', 'r')
  16       text = pipe.read()
  17       sts = pipe.close()
  18
  19  [Note:  it would be nice to add functions to interpret the exit status.]
  20 """
  21
  22 __all__ = ["getstatusoutput","getoutput","getstatus"]
  23
  24 # Module 'commands'
  25 #
  26 # Various tools for executing commands and looking at their output and status.
  27 #
  28 # NB This only works (and is only relevant) for UNIX.
  29
  30
  31 # Get 'ls -l' status for an object into a string
  32 #
  33 def getstatus(file):
  34     """Return output of "ls -ld <file>" in a string."""
  35     return getoutput('ls -ld' + mkarg(file))
  36
  37
  38 # Get the output from a shell command into a string.
  39 # The exit status is ignored; a trailing newline is stripped.
  40 # Assume the command will work with '{ ... ; } 2>&1' around it..
  41 #
  42 def getoutput(cmd):
  43     """Return output (stdout or stderr) of executing cmd in a shell."""
  44     return getstatusoutput(cmd)[1]
  45
  46
  47 # Ditto but preserving the exit status.
  48 # Returns a pair (sts, output)
  49 #
  50 def getstatusoutput(cmd):
  51     """Return (status, output) of executing cmd in a shell."""
  52     import os
  53     pipe = os.popen('{ ' + cmd + '; } 2>&1', 'r')
  54     text = pipe.read()
  55     sts = pipe.close()
  56     if sts is None: sts = 0
  57     if text[-1:] == '\n': text = text[:-1]
  58     return sts, text
  59
  60
  61 # Make command argument from directory and pathname (prefix space, add quotes).
  62 #
  63 def mk2arg(head, x):
  64     import os
  65     return mkarg(os.path.join(head, x))
  66
  67
  68 # Make a shell command argument from a string.
  69 # Return a string beginning with a space followed by a shell-quoted
  70 # version of the argument.
  71 # Two strategies: enclose in single quotes if it contains none;
  72 # otherwise, enclose in double quotes and prefix quotable characters
  73 # with backslash.
  74 #
  75 def mkarg(x):
  76     if '\'' not in x:
  77         return ' \'' + x + '\''
  78     s = ' "'
  79     for c in x:
  80         if c in '\\$"`':
  81             s = s + '\\'
  82         s = s + c
  83     s = s + '"'
  84     return s