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.
File::Which searches the directories of the users 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, itll 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
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 95, 98, ME, MS-DOS, OS/2
This set of operating systems dont 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 its 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.
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
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
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
If it does not find the executable, it returns undef.
If which() is called in list context, it will return all the
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.