mingw/html/lib/filetest.html

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   5 <title>filetest - Perl pragma to control the filetest permission operators</title>
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  13 <big><strong><span class="block">&nbsp;filetest - Perl pragma to control the filetest permission operators</span></strong></big>
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  20 <ul>
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  22         <li><a href="#name">NAME</a></li>
  23         <li><a href="#synopsis">SYNOPSIS</a></li>
  24         <li><a href="#description">DESCRIPTION</a></li>
  25         <ul>
  26
  27                 <li><a href="#subpragma_access">subpragma access</a></li>
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  36 <h1><a name="name">NAME</a></h1>
  37 <p>filetest - Perl pragma to control the filetest permission operators</p>
  38 <p>
  39 </p>
  40 <hr />
  41 <h1><a name="synopsis">SYNOPSIS</a></h1>
  42 <pre>
  43     $can_perhaps_read = -r &quot;file&quot;;      # use the mode bits
  44     {
  45         use filetest 'access';          # intuit harder
  46         $can_really_read = -r &quot;file&quot;;
  47     }
  48     $can_perhaps_read = -r &quot;file&quot;;      # use the mode bits again</pre>
  49 <p>
  50 </p>
  51 <hr />
  52 <h1><a name="description">DESCRIPTION</a></h1>
  53 <p>This pragma tells the compiler to change the behaviour of the filetest
  54 permission operators, <code>-r</code> <code>-w</code> <code>-x</code> <code>-R</code> <code>-W</code> <a href="file://C|\msysgit\mingw\html/pod/perlfunc.html#item__2dx"><code>-X</code></a>
  55 (see <a href="file://C|\msysgit\mingw\html/pod/perlfunc.html">the perlfunc manpage</a>).</p>
  56 <p>The default behaviour is to use the mode bits as returned by the <a href="file://C|\msysgit\mingw\html/pod/perlfunc.html#item_stat"><code>stat()</code></a>
  57 family of calls.  This, however, may not be the right thing to do if
  58 for example various ACL (access control lists) schemes are in use.
  59 For such environments, <code>use filetest</code> may help the permission
  60 operators to return results more consistent with other tools.</p>
  61 <p>Each ``use filetest'' or ``no filetest'' affects statements to the end of
  62 the enclosing block.</p>
  63 <p>There may be a slight performance decrease in the filetests
  64 when <code>use filetest</code> is in effect, because in some systems
  65 the extended functionality needs to be emulated.</p>
  66 <p><strong>NOTE</strong>: using the file tests for security purposes is a lost cause
  67 from the start: there is a window open for race conditions (who is to
  68 say that the permissions will not change between the test and the real
  69 operation?).  Therefore if you are serious about security, just try
  70 the real operation and test for its success - think in terms of atomic
  71 operations.</p>
  72 <p>
  73 </p>
  74 <h2><a name="subpragma_access">subpragma access</a></h2>
  75 <p>Currently only one subpragma, <code>access</code> is implemented.  It enables
  76 (or disables) the use of <code>access()</code> or similar system calls.  This
  77 extended filetest functionality is used only when the argument of the
  78 operators is a filename, not when it is a filehandle.</p>
  79 <table border="0" width="100%" cellspacing="0" cellpadding="3">
  80 <tr><td class="block" style="background-color: #cccccc" valign="middle">
  81 <big><strong><span class="block">&nbsp;filetest - Perl pragma to control the filetest permission operators</span></strong></big>
  82 </td></tr>
  83 </table>
  84
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