file::which.3

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.\" ========================================================================
.\"
.IX Title "Which 3"
.TH Which 3 "2002-06-24" "perl v5.10.0" "User Contributed Perl Documentation"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
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.SH "NAME"
File::Which \- Portable implementation of the `which' utility
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 2
\&  use File::Which;                  # exports which()
\&  use File::Which qw(which where);  # exports which() and where()
\&  
\&  my $exe_path = which(\*(Aqperldoc\*(Aq);
\&  
\&  my @paths = where(\*(Aqperl\*(Aq);
\&  \- Or \-
\&  my @paths = which(\*(Aqperl\*(Aq); # an array forces search for all of them
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
\&\f(CW\*(C`File::Which\*(C'\fR was created to be able to get the paths to executable programs
on systems under which the `which' program wasn't implemented in the shell.
.PP
\&\f(CW\*(C`File::Which\*(C'\fR searches the directories of the user's \f(CW\*(C`PATH\*(C'\fR (as returned by
\&\f(CW\*(C`File::Spec\->path()\*(C'\fR), looking for executable files having the name specified
as a parameter to \f(CW\*(C`which()\*(C'\fR. Under Win32 systems, which do not have a notion of
directly executable files, but uses special extensions such as \f(CW\*(C`.exe\*(C'\fR and
\&\f(CW\*(C`.bat\*(C'\fR to identify them, \f(CW\*(C`File::Which\*(C'\fR takes extra steps to assure that you
will find the correct file (so for example, you might be searching for \f(CW\*(C`perl\*(C'\fR,
it'll try \f(CW\*(C`perl.exe\*(C'\fR, \f(CW\*(C`perl.bat\*(C'\fR, etc.)
.SH "Steps Used on Win32, DOS, OS2 and VMS"
.IX Header "Steps Used on Win32, DOS, OS2 and VMS"
.Sh "Windows \s-1NT\s0"
.IX Subsection "Windows NT"
Windows \s-1NT\s0 has a special environment variable called \f(CW\*(C`PATHEXT\*(C'\fR, which is used
by the shell to look for executable files. Usually, it will contain a list in
the form \f(CW\*(C`.EXE;.BAT;.COM;.JS;.VBS\*(C'\fR etc. If \f(CW\*(C`File::Which\*(C'\fR finds such an
environment variable, it parses the list and uses it as the different extensions.
.Sh "Windows 9x and other ancient Win/DOS/OS2"
.IX Subsection "Windows 9x and other ancient Win/DOS/OS2"
This set of operating systems don't have the \f(CW\*(C`PATHEXT\*(C'\fR variable, and usually
you will find executable files there with the extensions \f(CW\*(C`.exe\*(C'\fR, \f(CW\*(C`.bat\*(C'\fR and
(less likely) \f(CW\*(C`.com\*(C'\fR. \f(CW\*(C`File::Which\*(C'\fR uses this hardcoded list if it's running
under Win32 but does not find a \f(CW\*(C`PATHEXT\*(C'\fR variable.
.Sh "\s-1VMS\s0"
.IX Subsection "VMS"
Same case as Windows 9x: uses \f(CW\*(C`.exe\*(C'\fR and \f(CW\*(C`.com\*(C'\fR (in that order).
.SH "Functions"
.IX Header "Functions"
.Sh "which($short_exe_name)"
.IX Subsection "which($short_exe_name)"
Exported by default.
.PP
\&\f(CW$short_exe_name\fR is the name used in the shell to call the program (for
example, \f(CW\*(C`perl\*(C'\fR).
.PP
If it finds an executable with the name you specified, \f(CW\*(C`which()\*(C'\fR will return
the absolute path leading to this executable (for example, \f(CW\*(C`/usr/bin/perl\*(C'\fR or
\&\f(CW\*(C`C:\ePerl\eBin\eperl.exe\*(C'\fR).
.PP
If it does \fInot\fR find the executable, it returns \f(CW\*(C`undef\*(C'\fR.
.PP
If \f(CW\*(C`which()\*(C'\fR is called in list context, it will return \fIall\fR the
matches.
.Sh "where($short_exe_name)"
.IX Subsection "where($short_exe_name)"
Not exported by default.
.PP
Same as \f(CW\*(C`which($short_exe_name)\*(C'\fR in array context. Same as the
\&\f(CW\`where\*(Aq\fR utility, will return an array containing all the path names
matching \f(CW$short_exe_name\fR.
.SH "Bugs and Caveats"
.IX Header "Bugs and Caveats"
Not tested on \s-1VMS\s0 or MacOS, although there is platform specific code
for those. Anyone who haves a second would be very kind to send me a
report of how it went.
.PP
File::Spec adds the current directory to the front of \s-1PATH\s0 if on
Win32, \s-1VMS\s0 or MacOS. I have no knowledge of those so don't know if the
current directory is searced first or not. Could someone please tell
me?
.SH "Author"
.IX Header "Author"
Per Einar Ellefsen, <per.einar (at) skynet.be>
.PP
Originated in \fImodperl\-2.0/lib/Apache/Build.pm\fR. Changed for use in DocSet
(for the mod_perl site) and Win32\-awareness by me, with slight modifications
by Stas Bekman, then extracted to create \f(CW\*(C`File::Which\*(C'\fR.
.PP
Version 0.04 had some significant platform-related changes, taken from
the Perl Power Tools \f(CW\`which\*(Aq\fR implementation by Abigail with
enhancements from Peter Prymmer. See
http://www.perl.com/language/ppt/src/which/index.html for more
information.
.SH "License"
.IX Header "License"
This library is free software; you can redistribute it and/or modify it under
the same terms as Perl itself.
.SH "See Also"
.IX Header "See Also"
File::Spec, \fIwhich\fR\|(1), Perl Power Tools:
http://www.perl.com/language/ppt/index.html .