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NAME
File::Which - Perl implementation of the which utility as an API
VERSION
version 1.23
SYNOPSIS
use File::Which; # exports which()
use File::Which qw(which where); # exports which() and where()
my $exe_path = which 'perldoc';
my @paths = where 'perl';
# Or
my @paths = which 'perl'; # an array forces search for all of them
DESCRIPTION
File::Which finds the full or relative paths to executable programs on
the system. This is normally the function of which utility. which is
typically implemented as either a program or a built in shell command.
On some platforms, such as Microsoft Windows it is not provided as part
of the core operating system. This module provides a consistent API to
this functionality regardless of the underlying platform.
The focus of this module is correctness and portability. As a
consequence platforms where the current directory is implicitly part of
the search path such as Microsoft Windows will find executables in the
current directory, whereas on platforms such as UNIX where this is not
the case executables in the current directory will only be found if the
current directory is explicitly added to the path.
If you need a portable which on the command line in an environment that
does not provide it, install App::pwhich which provides a command line
interface to this API.
Implementations
File::Which searches the directories of the user's PATH (the current
implementation uses File::Spec#path to determine the correct PATH),
looking for executable files having the name specified as a parameter
to "which". Under Win32 systems, which do not have a notion of directly
executable files, but uses special extensions such as .exe and .bat to
identify them, File::Which takes extra steps to assure that you will
find the correct file (so for example, you might be searching for perl,
it'll try perl.exe, perl.bat, etc.)
Linux, *BSD and other UNIXes
There should not be any surprises here. The current directory will not
be searched unless it is explicitly added to the path.
Modern Windows (including NT, XP, Vista, 7, 8, 10 etc)
Windows NT has a special environment variable called PATHEXT, which is
used by the shell to look for executable files. Usually, it will
contain a list in the form .EXE;.BAT;.COM;.JS;.VBS etc. If File::Which
finds such an environment variable, it parses the list and uses it as
the different extensions.
Cygwin
Cygwin provides a Unix-like environment for Microsoft Windows users. In
most ways it works like other Unix and Unix-like environments, but in a
few key aspects it works like Windows. As with other Unix environments,
the current directory is not included in the search unless it is
explicitly included in the search path. Like on Windows, files with
.EXE or <.BAT> extensions will be discovered even if they are not part
of the query. .COM or extensions specified using the PATHEXT
environment variable will NOT be discovered without the fully qualified
name, however.
Windows ME, 98, 95, MS-DOS, OS/2
This set of operating systems don't have the PATHEXT variable, and
usually you will find executable files there with the extensions .exe,
.bat and (less likely) .com. File::Which uses this hardcoded list if
it's running under Win32 but does not find a PATHEXT variable.
As of 2015 none of these platforms are tested frequently (or perhaps
ever), but the current maintainer is determined not to intentionally
remove support for older operating systems.
VMS
Same case as Windows 9x: uses .exe and .com (in that order).
As of 2015 the current maintainer does not test on VMS, and is in fact
not certain it has ever been tested on VMS. If this platform is
important to you and you can help me verify and or support it on that
platform please contact me.
FUNCTIONS
which
my $path = which $short_exe_name;
my @paths = which $short_exe_name;
Exported by default.
$short_exe_name is the name used in the shell to call the program (for
example, perl).
If it finds an executable with the name you specified, which() will
return the absolute path leading to this executable (for example,
/usr/bin/perl or C:\Perl\Bin\perl.exe).
If it does not find the executable, it returns undef.
If which() is called in list context, it will return all the matches.
where
my @paths = where $short_exe_name;
Not exported by default.
Same as "which" in array context. Similar to the where csh built-in
command or which -a command for platforms that support the -a option.
Will return an array containing all the path names matching
$short_exe_name.
GLOBALS
$IMPLICIT_CURRENT_DIR
True if the current directory is included in the search implicitly on
whatever platform you are using. Normally the default is reasonable,
but on Windows the current directory is included implicitly for older
shells like cmd.exe and command.com, but not for newer shells like
PowerShell. If you overrule this default, you should ALWAYS localize
the variable to the tightest scope possible, since setting this
variable from a module can affect other modules. Thus on Windows you
can get the correct result if the user is running either cmd.exe or
PowerShell on Windows you can do this:
use File::Which qw( which );
use Shell::Guess;
my $path = do {
my $is_power = Shell::Guess->running_shell->is_power;
local $File::Which::IMPLICIT_CURRENT_DIR = !$is_power;
which 'foo';
};
For a variety of reasons it is difficult to accurately compute the
shell that a user is using, but Shell::Guess makes a reasonable effort.
CAVEATS
This module has no non-core requirements for Perl 5.6.2 and better.
This module is fully supported back to Perl 5.8.1. It may work on
5.8.0. It should work on Perl 5.6.x and I may even test on 5.6.2. I
will accept patches to maintain compatibility for such older Perls, but
you may need to fix it on 5.6.x / 5.8.0 and send me a patch.
Not tested on VMS 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.
SUPPORT
Bugs should be reported via the GitHub issue tracker
https://github.com/plicease/File-Which/issues
For other issues, contact the maintainer.
SEE ALSO
pwhich, App::pwhich
Command line interface to this module.
IPC::Cmd
This module provides (among other things) a can_run function, which
is similar to which. It is a much heavier module since it does a lot
more, and if you use can_run it pulls in ExtUtils::MakeMaker. This
combination may be overkill for applications which do not need
IPC::Cmd's complicated interface for running programs, or do not need
the memory overhead required for installing Perl modules.
At least some older versions will find executables in the current
directory, even if the current directory is not in the search path
(which is the default on modern Unix).
can_run converts directory path name to the 8.3 version on Windows
using Win32::GetShortPathName in some cases. This is frequently
useful for tools that just need to run something using system in
scalar mode, but may be inconvenient for tools like App::pwhich where
user readability is a premium. Relying on Win32::GetShortPathName to
produce filenames without spaces is problematic, as 8.3 filenames can
be turned off with tweaks to the registry (see
https://technet.microsoft.com/en-us/library/cc959352.aspx).
Devel::CheckBin
This module purports to "check that a command is available", but does
not provide any documentation on how you might use it.
AUTHORS
* Per Einar Ellefsen <pereinar@cpan.org>
* Adam Kennedy <adamk@cpan.org>
* Graham Ollis <plicease@cpan.org>
COPYRIGHT AND LICENSE
This software is copyright (c) 2002 by Per Einar Ellefsen
<pereinar@cpan.org>.
This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.
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