mingw/html/pod/perlform.html

   1 <?xml version="1.0" ?>
   2 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
   3 <html xmlns="http://www.w3.org/1999/xhtml">
   4 <head>
   5 <title>perlform - Perl formats</title>
   6 <meta http-equiv="content-type" content="text/html; charset=utf-8" />
   7 <link rev="made" href="mailto:" />
   8 </head>
   9
  10 <body style="background-color: white">
  11 <table border="0" width="100%" cellspacing="0" cellpadding="3">
  12 <tr><td class="block" style="background-color: #cccccc" valign="middle">
  13 <big><strong><span class="block">&nbsp;perlform - Perl formats</span></strong></big>
  14 </td></tr>
  15 </table>
  16
  17 <p><a name="__index__"></a></p>
  18 <!-- INDEX BEGIN -->
  19
  20 <ul>
  21
  22         <li><a href="#name">NAME</a></li>
  23         <li><a href="#description">DESCRIPTION</a></li>
  24         <ul>
  25
  26                 <li><a href="#text_fields">Text Fields</a></li>
  27                 <li><a href="#numeric_fields">Numeric Fields</a></li>
  28                 <li><a href="#the_field____for_variable_width_multiline_text">The Field @* for Variable Width Multi-Line Text</a></li>
  29                 <li><a href="#the_field____for_variable_width_onelineatatime_text">The Field ^* for Variable Width One-line-at-a-time Text</a></li>
  30                 <li><a href="#specifying_values">Specifying Values</a></li>
  31                 <li><a href="#using_fill_mode">Using Fill Mode</a></li>
  32                 <li><a href="#suppressing_lines_where_all_fields_are_void">Suppressing Lines Where All Fields Are Void</a></li>
  33                 <li><a href="#repeating_format_lines">Repeating Format Lines</a></li>
  34                 <li><a href="#top_of_form_processing">Top of Form Processing</a></li>
  35                 <li><a href="#format_variables">Format Variables</a></li>
  36         </ul>
  37
  38         <li><a href="#notes">NOTES</a></li>
  39         <ul>
  40
  41                 <li><a href="#footers">Footers</a></li>
  42                 <li><a href="#accessing_formatting_internals">Accessing Formatting Internals</a></li>
  43         </ul>
  44
  45         <li><a href="#warnings">WARNINGS</a></li>
  46 </ul>
  47 <!-- INDEX END -->
  48
  49 <hr />
  50 <p>
  51 </p>
  52 <h1><a name="name_x_format__x_report__x_chart_">NAME
  53   </a></h1>
  54 <p>perlform - Perl formats</p>
  55 <p>
  56 </p>
  57 <hr />
  58 <h1><a name="description">DESCRIPTION</a></h1>
  59 <p>Perl has a mechanism to help you generate simple reports and charts.  To
  60 facilitate this, Perl helps you code up your output page close to how it
  61 will look when it's printed.  It can keep track of things like how many
  62 lines are on a page, what page you're on, when to print page headers,
  63 etc.  Keywords are borrowed from FORTRAN: <code>format()</code> to declare and <a href="file://C|\msysgit\mingw\html/pod/perlfunc.html#item_write"><code>write()</code></a>
  64 to execute; see their entries in <a href="file://C|\msysgit\mingw\html/pod/perlfunc.html">the perlfunc manpage</a>.  Fortunately, the layout is
  65 much more legible, more like BASIC's PRINT USING statement.  Think of it
  66 as a poor man's nroff(1).
  67 </p>
  68 <p>Formats, like packages and subroutines, are declared rather than
  69 executed, so they may occur at any point in your program.  (Usually it's
  70 best to keep them all together though.) They have their own namespace
  71 apart from all the other ``types'' in Perl.  This means that if you have a
  72 function named ``Foo'', it is not the same thing as having a format named
  73 ``Foo''.  However, the default name for the format associated with a given
  74 filehandle is the same as the name of the filehandle.  Thus, the default
  75 format for STDOUT is named ``STDOUT'', and the default format for filehandle
  76 TEMP is named ``TEMP''.  They just look the same.  They aren't.</p>
  77 <p>Output record formats are declared as follows:</p>
  78 <pre>
  79     format NAME =
  80     FORMLIST
  81     .</pre>
  82 <p>If the name is omitted, format ``STDOUT'' is defined. A single ``.'' in
  83 column 1 is used to terminate a format.  FORMLIST consists of a sequence
  84 of lines, each of which may be one of three types:</p>
  85 <ol>
  86 <li>
  87 <p>A comment, indicated by putting a '#' in the first column.</p>
  88 </li>
  89 <li>
  90 <p>A ``picture'' line giving the format for one output line.</p>
  91 </li>
  92 <li>
  93 <p>An argument line supplying values to plug into the previous picture line.</p>
  94 </li>
  95 </ol>
  96 <p>Picture lines contain output field definitions, intermingled with
  97 literal text. These lines do not undergo any kind of variable interpolation.
  98 Field definitions are made up from a set of characters, for starting and
  99 extending a field to its desired width. This is the complete set of
 100 characters for field definitions:
 101
 102   &gt; &gt;  &gt;&gt;
 103
 104 </p>
 105 <pre>
 106
 107    @    start of regular field
 108    ^    start of special field
 109    &lt;    pad character for left adjustification
 110    |    pad character for centering
 111    &gt;    pad character for right adjustificat
 112    #    pad character for a right justified numeric field
 113    0    instead of first #: pad number with leading zeroes
 114    .    decimal point within a numeric field
 115    ...  terminate a text field, show &quot;...&quot; as truncation evidence
 116    @*   variable width field for a multi-line value
 117    ^*   variable width field for next line of a multi-line value
 118    ~    suppress line with all fields empty
 119    ~~   repeat line until all fields are exhausted</pre>
 120 <p>Each field in a picture line starts with either ``@'' (at) or ``^'' (caret),
 121 indicating what we'll call, respectively, a ``regular'' or ``special'' field.
 122 The choice of pad characters determines whether a field is textual or
 123 numeric. The tilde operators are not part of a field.  Let's look at
 124 the various possibilities in detail.</p>
 125 <p>
 126 </p>
 127 <h2><a name="text_fields_x_format__text_field_">Text Fields
 128 </a></h2>
 129 <p>The length of the field is supplied by padding out the field with multiple
 130 ``&lt;'', ``&gt;'', or ``|'' characters to specify a non-numeric field with,
 131 respectively, left justification, right justification, or centering.
 132 For a regular field, the value (up to the first newline) is taken and
 133 printed according to the selected justification, truncating excess characters.
 134 If you terminate a text field with ``...'', three dots will be shown if
 135 the value is truncated. A special text field may be used to do rudimentary
 136 multi-line text block filling; see <a href="#using_fill_mode">Using Fill Mode</a> for details.</p>
 137 <pre>
 138    Example:
 139       format STDOUT =
 140       @&lt;&lt;&lt;&lt;&lt;&lt;   @||||||   @&gt;&gt;&gt;&gt;&gt;&gt;
 141       &quot;left&quot;,   &quot;middle&quot;, &quot;right&quot;
 142       .
 143    Output:
 144       left      middle    right</pre>
 145 <p>
 146 </p>
 147 <h2><a name="numeric_fields_x____x_format__numeric_field_">Numeric Fields
 148  </a></h2>
 149 <p>Using ``#'' as a padding character specifies a numeric field, with
 150 right justification. An optional ``.'' defines the position of the
 151 decimal point. With a ``0'' (zero) instead of the first ``#'', the
 152 formatted number will be padded with leading zeroes if necessary.
 153 A special numeric field is blanked out if the value is undefined.
 154 If the resulting value would exceed the width specified the field is
 155 filled with ``#'' as overflow evidence.</p>
 156 <pre>
 157    Example:
 158       format STDOUT =
 159       @###   @.###   @##.###  @###   @###   ^####
 160        42,   3.1415,  undef,    0, 10000,   undef
 161       .
 162    Output:
 163         42   3.142     0.000     0   ####</pre>
 164 <p>
 165 </p>
 166 <h2><a name="the_field____for_variable_width_multiline_text_x____">The Field @* for Variable Width Multi-Line Text
 167 </a></h2>
 168 <p>The field ``@*'' can be used for printing multi-line, nontruncated
 169 values; it should (but need not) appear by itself on a line. A final
 170 line feed is chomped off, but all other characters are emitted verbatim.</p>
 171 <p>
 172 </p>
 173 <h2><a name="the_field____for_variable_width_onelineatatime_text_x____">The Field ^* for Variable Width One-line-at-a-time Text
 174 </a></h2>
 175 <p>Like ``@*'', this is a variable width field. The value supplied must be a
 176 scalar variable. Perl puts the first line (up to the first ``\n'') of the
 177 text into the field, and then chops off the front of the string so that
 178 the next time the variable is referenced, more of the text can be printed.
 179 The variable will <em>not</em> be restored.</p>
 180 <pre>
 181    Example:
 182       $text = &quot;line 1\nline 2\nline 3&quot;;
 183       format STDOUT =
 184       Text: ^*
 185             $text
 186       ~~    ^*
 187             $text
 188       .
 189    Output:
 190       Text: line 1
 191             line 2
 192             line 3</pre>
 193 <p>
 194 </p>
 195 <h2><a name="specifying_values_x_format__specifying_values_">Specifying Values
 196 </a></h2>
 197 <p>The values are specified on the following format line in the same order as
 198 the picture fields.  The expressions providing the values must be
 199 separated by commas.  They are all evaluated in a list context
 200 before the line is processed, so a single list expression could produce
 201 multiple list elements.  The expressions may be spread out to more than
 202 one line if enclosed in braces.  If so, the opening brace must be the first
 203 token on the first line.  If an expression evaluates to a number with a
 204 decimal part, and if the corresponding picture specifies that the decimal
 205 part should appear in the output (that is, any picture except multiple ``#''
 206 characters <strong>without</strong> an embedded ``.''), the character used for the decimal
 207 point is <strong>always</strong> determined by the current LC_NUMERIC locale.  This
 208 means that, if, for example, the run-time environment happens to specify a
 209 German locale, ``,'' will be used instead of the default ``.''.  See
 210 <a href="file://C|\msysgit\mingw\html/pod/perllocale.html">the perllocale manpage</a> and <a href="#warnings">WARNINGS</a> for more information.</p>
 211 <p>
 212 </p>
 213 <h2><a name="using_fill_mode_x_format__fill_mode_">Using Fill Mode
 214 </a></h2>
 215 <p>On text fields the caret enables a kind of fill mode.  Instead of an
 216 arbitrary expression, the value supplied must be a scalar variable
 217 that contains a text string.  Perl puts the next portion of the text into
 218 the field, and then chops off the front of the string so that the next time
 219 the variable is referenced, more of the text can be printed.  (Yes, this
 220 means that the variable itself is altered during execution of the <a href="file://C|\msysgit\mingw\html/pod/perlfunc.html#item_write"><code>write()</code></a>
 221 call, and is not restored.)  The next portion of text is determined by
 222 a crude line breaking algorithm. You may use the carriage return character
 223 (<code>\r</code>) to force a line break. You can change which characters are legal
 224 to break on by changing the variable <a href="file://C|\msysgit\mingw\html/pod/perlvar.html#item___"><code>$:</code></a> (that's
 225 $FORMAT_LINE_BREAK_CHARACTERS if you're using the English module) to a
 226 list of the desired characters.</p>
 227 <p>Normally you would use a sequence of fields in a vertical stack associated
 228 with the same scalar variable to print out a block of text. You might wish
 229 to end the final field with the text ``...'', which will appear in the output
 230 if the text was too long to appear in its entirety.</p>
 231 <p>
 232 </p>
 233 <h2><a name="suppressing_lines_where_all_fields_are_void_x_format__suppressing_lines_">Suppressing Lines Where All Fields Are Void
 234 </a></h2>
 235 <p>Using caret fields can produce lines where all fields are blank. You can
 236 suppress such lines by putting a ``~'' (tilde) character anywhere in the
 237 line.  The tilde will be translated to a space upon output.</p>
 238 <p>
 239 </p>
 240 <h2><a name="repeating_format_lines_x_format__repeating_lines_">Repeating Format Lines
 241 </a></h2>
 242 <p>If you put two contiguous tilde characters ``~~'' anywhere into a line,
 243 the line will be repeated until all the fields on the line are exhausted,
 244 i.e. undefined. For special (caret) text fields this will occur sooner or
 245 later, but if you use a text field of the at variety, the  expression you
 246 supply had better not give the same value every time forever! (<a href="file://C|\msysgit\mingw\html/pod/perlfunc.html#item_shift"><code>shift(@f)</code></a>
 247 is a simple example that would work.)  Don't use a regular (at) numeric
 248 field in such lines, because it will never go blank.</p>
 249 <p>
 250 </p>
 251 <h2><a name="top_of_form_processing_x_format__top_of_form__x_top__x_header_">Top of Form Processing
 252   </a></h2>
 253 <p>Top-of-form processing is by default handled by a format with the
 254 same name as the current filehandle with ``_TOP'' concatenated to it.
 255 It's triggered at the top of each page.  See <a href="file://C|\msysgit\mingw\html/pod/perlfunc.html#item_write">write in the perlfunc manpage</a>.</p>
 256 <p>Examples:</p>
 257 <pre>
 258  # a report on the /etc/passwd file
 259  format STDOUT_TOP =
 260                          Passwd File
 261  Name                Login    Office   Uid   Gid Home
 262  ------------------------------------------------------------------
 263  .
 264  format STDOUT =
 265  @&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt; @||||||| @&lt;&lt;&lt;&lt;&lt;&lt;@&gt;&gt;&gt;&gt; @&gt;&gt;&gt;&gt; @&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;
 266  $name,              $login,  $office,$uid,$gid, $home
 267  .</pre>
 268 <pre>
 269  # a report from a bug report form
 270  format STDOUT_TOP =
 271                          Bug Reports
 272  @&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;     @|||         @&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;
 273  $system,                      $%,         $date
 274  ------------------------------------------------------------------
 275  .
 276  format STDOUT =
 277  Subject: @&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;
 278           $subject
 279  Index: @&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt; ^&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;
 280         $index,                       $description
 281  Priority: @&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt; Date: @&lt;&lt;&lt;&lt;&lt;&lt;&lt; ^&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;
 282            $priority,        $date,   $description
 283  From: @&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt; ^&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;
 284        $from,                         $description
 285  Assigned to: @&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt; ^&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;
 286               $programmer,            $description
 287  ~                                    ^&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;
 288                                       $description
 289  ~                                    ^&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;
 290                                       $description
 291  ~                                    ^&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;
 292                                       $description
 293  ~                                    ^&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;
 294                                       $description
 295  ~                                    ^&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;...
 296                                       $description
 297  .</pre>
 298 <p>It is possible to intermix print()s with write()s on the same output
 299 channel, but you'll have to handle <a href="file://C|\msysgit\mingw\html/pod/perlvar.html#item__"><code>$-</code></a> (<a href="file://C|\msysgit\mingw\html/pod/perlvar.html#item__format_lines_left"><code>$FORMAT_LINES_LEFT</code></a>)
 300 yourself.</p>
 301 <p>
 302 </p>
 303 <h2><a name="format_variables_x_format_variables__x_format__variables_">Format Variables
 304
 305 </a></h2>
 306 <p>The current format name is stored in the variable <a href="file://C|\msysgit\mingw\html/pod/perlvar.html#item___"><code>$~</code></a> (<a href="file://C|\msysgit\mingw\html/pod/perlvar.html#item__format_name"><code>$FORMAT_NAME</code></a>),
 307 and the current top of form format name is in <a href="file://C|\msysgit\mingw\html/pod/perlvar.html#item___"><code>$^</code></a> (<a href="file://C|\msysgit\mingw\html/pod/perlvar.html#item__format_top_name"><code>$FORMAT_TOP_NAME</code></a>).
 308 The current output page number is stored in <a href="file://C|\msysgit\mingw\html/pod/perlvar.html#item___"><code>$%</code></a> (<a href="file://C|\msysgit\mingw\html/pod/perlvar.html#item__format_page_number"><code>$FORMAT_PAGE_NUMBER</code></a>),
 309 and the number of lines on the page is in <a href="file://C|\msysgit\mingw\html/pod/perlvar.html#item___"><code>$=</code></a> (<a href="file://C|\msysgit\mingw\html/pod/perlvar.html#item__format_lines_per_page"><code>$FORMAT_LINES_PER_PAGE</code></a>).
 310 Whether to autoflush output on this handle is stored in <a href="file://C|\msysgit\mingw\html/pod/perlvar.html#item___"><code>$|</code></a>
 311 (<a href="file://C|\msysgit\mingw\html/pod/perlvar.html#item__output_autoflush"><code>$OUTPUT_AUTOFLUSH</code></a>).  The string output before each top of page (except
 312 the first) is stored in <a href="file://C|\msysgit\mingw\html/pod/perlvar.html#item___l"><code>$^L</code></a> (<a href="file://C|\msysgit\mingw\html/pod/perlvar.html#item__format_formfeed"><code>$FORMAT_FORMFEED</code></a>).  These variables are
 313 set on a per-filehandle basis, so you'll need to <a href="file://C|\msysgit\mingw\html/pod/perlfunc.html#item_select"><code>select()</code></a> into a different
 314 one to affect them:</p>
 315 <pre>
 316     select((select(OUTF),
 317             $~ = &quot;My_Other_Format&quot;,
 318             $^ = &quot;My_Top_Format&quot;
 319            )[0]);</pre>
 320 <p>Pretty ugly, eh?  It's a common idiom though, so don't be too surprised
 321 when you see it.  You can at least use a temporary variable to hold
 322 the previous filehandle: (this is a much better approach in general,
 323 because not only does legibility improve, you now have intermediary
 324 stage in the expression to single-step the debugger through):</p>
 325 <pre>
 326     $ofh = select(OUTF);
 327     $~ = &quot;My_Other_Format&quot;;
 328     $^ = &quot;My_Top_Format&quot;;
 329     select($ofh);</pre>
 330 <p>If you use the English module, you can even read the variable names:</p>
 331 <pre>
 332     use English '-no_match_vars';
 333     $ofh = select(OUTF);
 334     $FORMAT_NAME     = &quot;My_Other_Format&quot;;
 335     $FORMAT_TOP_NAME = &quot;My_Top_Format&quot;;
 336     select($ofh);</pre>
 337 <p>But you still have those funny select()s.  So just use the FileHandle
 338 module.  Now, you can access these special variables using lowercase
 339 method names instead:</p>
 340 <pre>
 341     use FileHandle;
 342     format_name     OUTF &quot;My_Other_Format&quot;;
 343     format_top_name OUTF &quot;My_Top_Format&quot;;</pre>
 344 <p>Much better!</p>
 345 <p>
 346 </p>
 347 <hr />
 348 <h1><a name="notes">NOTES</a></h1>
 349 <p>Because the values line may contain arbitrary expressions (for at fields,
 350 not caret fields), you can farm out more sophisticated processing
 351 to other functions, like <code>sprintf()</code> or one of your own.  For example:</p>
 352 <pre>
 353     format Ident =
 354         @&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;
 355         &amp;commify($n)
 356     .</pre>
 357 <p>To get a real at or caret into the field, do this:</p>
 358 <pre>
 359     format Ident =
 360     I have an @ here.
 361             &quot;@&quot;
 362     .</pre>
 363 <p>To center a whole line of text, do something like this:</p>
 364 <pre>
 365     format Ident =
 366     @|||||||||||||||||||||||||||||||||||||||||||||||
 367             &quot;Some text line&quot;
 368     .</pre>
 369 <p>There is no builtin way to say ``float this to the right hand side
 370 of the page, however wide it is.''  You have to specify where it goes.
 371 The truly desperate can generate their own format on the fly, based
 372 on the current number of columns, and then <a href="file://C|\msysgit\mingw\html/pod/perlfunc.html#item_eval"><code>eval()</code></a> it:</p>
 373 <pre>
 374     $format  = &quot;format STDOUT = \n&quot;
 375              . '^' . '&lt;' x $cols . &quot;\n&quot;
 376              . '$entry' . &quot;\n&quot;
 377              . &quot;\t^&quot; . &quot;&lt;&quot; x ($cols-8) . &quot;~~\n&quot;
 378              . '$entry' . &quot;\n&quot;
 379              . &quot;.\n&quot;;
 380     print $format if $Debugging;
 381     eval $format;
 382     die $@ if $@;</pre>
 383 <p>Which would generate a format looking something like this:</p>
 384 <pre>
 385  format STDOUT =
 386  ^&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;
 387  $entry
 388          ^&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;~~
 389  $entry
 390  .</pre>
 391 <p>Here's a little program that's somewhat like fmt(1):</p>
 392 <pre>
 393  format =
 394  ^&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt; ~~
 395  $_</pre>
 396 <pre>
 397  .</pre>
 398 <pre>
 399  $/ = '';
 400  while (&lt;&gt;) {
 401      s/\s*\n\s*/ /g;
 402      write;
 403  }</pre>
 404 <p>
 405 </p>
 406 <h2><a name="footers_x_format__footer__x_footer_">Footers
 407  </a></h2>
 408 <p>While $FORMAT_TOP_NAME contains the name of the current header format,
 409 there is no corresponding mechanism to automatically do the same thing
 410 for a footer.  Not knowing how big a format is going to be until you
 411 evaluate it is one of the major problems.  It's on the TODO list.</p>
 412 <p>Here's one strategy:  If you have a fixed-size footer, you can get footers
 413 by checking $FORMAT_LINES_LEFT before each <a href="file://C|\msysgit\mingw\html/pod/perlfunc.html#item_write"><code>write()</code></a> and print the footer
 414 yourself if necessary.</p>
 415 <p>Here's another strategy: Open a pipe to yourself, using <a href="file://C|\msysgit\mingw\html/pod/perlfunc.html#item_open"><code>open(MYSELF, &quot;|-&quot;)</code></a>
 416 (see <a href="file://C|\msysgit\mingw\html/pod/perlfunc.html#item_open">open() in the perlfunc manpage</a>) and always <a href="file://C|\msysgit\mingw\html/pod/perlfunc.html#item_write"><code>write()</code></a> to MYSELF instead of STDOUT.
 417 Have your child process massage its STDIN to rearrange headers and footers
 418 however you like.  Not very convenient, but doable.</p>
 419 <p>
 420 </p>
 421 <h2><a name="accessing_formatting_internals_x_format__internals_">Accessing Formatting Internals
 422 </a></h2>
 423 <p>For low-level access to the formatting mechanism.  you may use <code>formline()</code>
 424 and access <a href="file://C|\msysgit\mingw\html/pod/perlvar.html#item___a"><code>$^A</code></a> (the $ACCUMULATOR variable) directly.</p>
 425 <p>For example:</p>
 426 <pre>
 427     $str = formline &lt;&lt;'END', 1,2,3;
 428     @&lt;&lt;&lt;  @|||  @&gt;&gt;&gt;
 429     END</pre>
 430 <pre>
 431     print &quot;Wow, I just stored `$^A' in the accumulator!\n&quot;;</pre>
 432 <p>Or to make an <code>swrite()</code> subroutine, which is to <a href="file://C|\msysgit\mingw\html/pod/perlfunc.html#item_write"><code>write()</code></a> what <code>sprintf()</code>
 433 is to printf(), do this:</p>
 434 <pre>
 435     use Carp;
 436     sub swrite {
 437         croak &quot;usage: swrite PICTURE ARGS&quot; unless @_;
 438         my $format = shift;
 439         $^A = &quot;&quot;;
 440         formline($format,@_);
 441         return $^A;
 442     }</pre>
 443 <pre>
 444     $string = swrite(&lt;&lt;'END', 1, 2, 3);
 445  Check me out
 446  @&lt;&lt;&lt;  @|||  @&gt;&gt;&gt;
 447  END
 448     print $string;</pre>
 449 <p>
 450 </p>
 451 <hr />
 452 <h1><a name="warnings">WARNINGS</a></h1>
 453 <p>The lone dot that ends a format can also prematurely end a mail
 454 message passing through a misconfigured Internet mailer (and based on
 455 experience, such misconfiguration is the rule, not the exception).  So
 456 when sending format code through mail, you should indent it so that
 457 the format-ending dot is not on the left margin; this will prevent
 458 SMTP cutoff.</p>
 459 <p>Lexical variables (declared with ``my'') are not visible within a
 460 format unless the format is declared within the scope of the lexical
 461 variable.  (They weren't visible at all before version 5.001.)</p>
 462 <p>Formats are the only part of Perl that unconditionally use information
 463 from a program's locale; if a program's environment specifies an
 464 LC_NUMERIC locale, it is always used to specify the decimal point
 465 character in formatted output.  Perl ignores all other aspects of locale
 466 handling unless the <code>use locale</code> pragma is in effect.  Formatted output
 467 cannot be controlled by <code>use locale</code> because the pragma is tied to the
 468 block structure of the program, and, for historical reasons, formats
 469 exist outside that block structure.  See <a href="file://C|\msysgit\mingw\html/pod/perllocale.html">the perllocale manpage</a> for further
 470 discussion of locale handling.</p>
 471 <p>Within strings that are to be displayed in a fixed length text field,
 472 each control character is substituted by a space. (But remember the
 473 special meaning of <code>\r</code> when using fill mode.) This is done to avoid
 474 misalignment when control characters ``disappear'' on some output media.
 475
 476 </p>
 477 <table border="0" width="100%" cellspacing="0" cellpadding="3">
 478 <tr><td class="block" style="background-color: #cccccc" valign="middle">
 479 <big><strong><span class="block">&nbsp;perlform - Perl formats</span></strong></big>
 480 </td></tr>
 481 </table>
 482
 483 </body>
 484
 485 </html>