1File::Which(3)        User Contributed Perl Documentation       File::Which(3)
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NAME

6       File::Which - Perl implementation of the which utility as an API
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VERSION

9       version 1.27
10

SYNOPSIS

12        use File::Which;                  # exports which()
13        use File::Which qw(which where);  # exports which() and where()
14
15        my $exe_path = which 'perldoc';
16
17        my @paths = where 'perl';
18        # Or
19        my @paths = which 'perl'; # an array forces search for all of them
20

DESCRIPTION

22       File::Which finds the full or relative paths to executable programs on
23       the system.  This is normally the function of "which" utility.  "which"
24       is typically implemented as either a program or a built in shell
25       command.  On some platforms, such as Microsoft Windows it is not
26       provided as part of the core operating system.  This module provides a
27       consistent API to this functionality regardless of the underlying
28       platform.
29
30       The focus of this module is correctness and portability.  As a
31       consequence platforms where the current directory is implicitly part of
32       the search path such as Microsoft Windows will find executables in the
33       current directory, whereas on platforms such as UNIX where this is not
34       the case executables in the current directory will only be found if the
35       current directory is explicitly added to the path.
36
37       If you need a portable "which" on the command line in an environment
38       that does not provide it, install App::pwhich which provides a command
39       line interface to this API.
40
41   Implementations
42       File::Which searches the directories of the user's "PATH" (the current
43       implementation uses File::Spec#path to determine the correct "PATH"),
44       looking for executable files having the name specified as a parameter
45       to "which". Under Win32 systems, which do not have a notion of directly
46       executable files, but uses special extensions such as ".exe" and ".bat"
47       to identify them, "File::Which" takes extra steps to assure that you
48       will find the correct file (so for example, you might be searching for
49       "perl", it'll try perl.exe, perl.bat, etc.)
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51       Linux, *BSD and other UNIXes
52
53       There should not be any surprises here.  The current directory will not
54       be searched unless it is explicitly added to the path.
55
56       Modern Windows (including NT, XP, Vista, 7, 8, 10 etc)
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58       Windows NT has a special environment variable called "PATHEXT", which
59       is used by the shell to look for executable files. Usually, it will
60       contain a list in the form ".EXE;.BAT;.COM;.JS;.VBS" etc. If
61       "File::Which" finds such an environment variable, it parses the list
62       and uses it as the different extensions.
63
64       Cygwin
65
66       Cygwin provides a Unix-like environment for Microsoft Windows users.
67       In most ways it works like other Unix and Unix-like environments, but
68       in a few key aspects it works like Windows.  As with other Unix
69       environments, the current directory is not included in the search
70       unless it is explicitly included in the search path.  Like on Windows,
71       files with ".EXE" or <.BAT> extensions will be discovered even if they
72       are not part of the query.  ".COM" or extensions specified using the
73       "PATHEXT" environment variable will NOT be discovered without the fully
74       qualified name, however.
75
76       Windows ME, 98, 95, MS-DOS, OS/2
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78       This set of operating systems don't have the "PATHEXT" variable, and
79       usually you will find executable files there with the extensions
80       ".exe", ".bat" and (less likely) ".com". "File::Which" uses this
81       hardcoded list if it's running under Win32 but does not find a
82       "PATHEXT" variable.
83
84       As of 2015 none of these platforms are tested frequently (or perhaps
85       ever), but the current maintainer is determined not to intentionally
86       remove support for older operating systems.
87
88       VMS
89
90       Same case as Windows 9x: uses ".exe" and ".com" (in that order).
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92       As of 2015 the current maintainer does not test on VMS, and is in fact
93       not certain it has ever been tested on VMS.  If this platform is
94       important to you and you can help me verify and or support it on that
95       platform please contact me.
96

FUNCTIONS

98   which
99        my $path = which $short_exe_name;
100        my @paths = which $short_exe_name;
101
102       Exported by default.
103
104       $short_exe_name is the name used in the shell to call the program (for
105       example, "perl").
106
107       If it finds an executable with the name you specified, which() will
108       return the absolute path leading to this executable (for example,
109       /usr/bin/perl or C:\Perl\Bin\perl.exe).
110
111       If it does not find the executable, it returns "undef".
112
113       If which() is called in list context, it will return all the matches.
114
115   where
116        my @paths = where $short_exe_name;
117
118       Not exported by default.
119
120       Same as "which" in array context.  Similar to the "where" csh built-in
121       command or "which -a" command for platforms that support the "-a"
122       option. Will return an array containing all the path names matching
123       $short_exe_name.
124

GLOBALS

126   $IMPLICIT_CURRENT_DIR
127       True if the current directory is included in the search implicitly on
128       whatever platform you are using.  Normally the default is reasonable,
129       but on Windows the current directory is included implicitly for older
130       shells like "cmd.exe" and "command.com", but not for newer shells like
131       PowerShell.  If you overrule this default, you should ALWAYS localize
132       the variable to the tightest scope possible, since setting this
133       variable from a module can affect other modules.  Thus on Windows you
134       can get the correct result if the user is running either "cmd.exe" or
135       PowerShell on Windows you can do this:
136
137        use File::Which qw( which );
138        use Shell::Guess;
139
140        my $path = do {
141          my $is_power = Shell::Guess->running_shell->is_power;
142          local $File::Which::IMPLICIT_CURRENT_DIR = !$is_power;
143          which 'foo';
144        };
145
146       For a variety of reasons it is difficult to accurately compute the
147       shell that a user is using, but Shell::Guess makes a reasonable effort.
148

CAVEATS

150       This module has no non-core requirements for Perl 5.6.2 and better.
151
152       This module is fully supported back to Perl 5.8.1.  It may work on
153       5.8.0.  It should work on Perl 5.6.x and I may even test on 5.6.2.  I
154       will accept patches to maintain compatibility for such older Perls, but
155       you may need to fix it on 5.6.x / 5.8.0 and send me a patch.
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157       Not tested on VMS although there is platform specific code for those.
158       Anyone who haves a second would be very kind to send me a report of how
159       it went.
160

SUPPORT

162       Bugs should be reported via the GitHub issue tracker
163
164       <https://github.com/uperl/File-Which/issues>
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166       For other issues, contact the maintainer.
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SEE ALSO

169       pwhich, App::pwhich
170           Command line interface to this module.
171
172       IPC::Cmd
173           Requires Perl 5.8.3.  Included as part of the Perl core as of
174           5.9.5.
175
176           This module provides (among other things) a "can_run" function,
177           which is similar to "which".  It is a much heavier module since it
178           does a lot more, and if you use "can_run" it pulls in
179           ExtUtils::MakeMaker.  This combination may be overkill for
180           applications which do not need IPC::Cmd's complicated interface for
181           running programs, or do not need the memory overhead required for
182           installing Perl modules.
183
184           At least some older versions will find executables in the current
185           directory, even if the current directory is not in the search path
186           (which is the default on modern Unix).
187
188           "can_run" converts directory path name to the 8.3 version on
189           Windows using "Win32::GetShortPathName" in some cases.  This is
190           frequently useful for tools that just need to run something using
191           "system" in scalar mode, but may be inconvenient for tools like
192           App::pwhich where user readability is a premium.  Relying on
193           "Win32::GetShortPathName" to produce filenames without spaces is
194           problematic, as 8.3 filenames can be turned off with tweaks to the
195           registry (see
196           <https://technet.microsoft.com/en-us/library/cc959352.aspx>).
197
198       Devel::CheckBin
199           Requires Perl 5.8.1.
200
201           This module purports to "check that a command is available", but
202           does not provide any documentation on how you might use it.
203
204           This module also relies on ExtUtils::MakeMaker so has the same
205           overhead burdens as IPC::Cmd.
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AUTHORS

208       •   Per Einar Ellefsen <pereinar@cpan.org>
209
210       •   Adam Kennedy <adamk@cpan.org>
211
212       •   Graham Ollis <plicease@cpan.org>
213
215       This software is copyright (c) 2002 by Per Einar Ellefsen
216       <pereinar@cpan.org>.
217
218       This is free software; you can redistribute it and/or modify it under
219       the same terms as the Perl 5 programming language system itself.
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223perl v5.36.0                      2023-01-20                    File::Which(3)
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