NAME
which -- display full pathname for executable command
SYNOPSIS
which [options] [command ...]
DESCRIPTION
DOS uses the PATH environment variable to determine which directories
to search when attempting to execute a program. For each command
specified, which searches directories defined in PATH and prints the
name of the first executable file that matches command. When /a or -a
is specified on the command line, which returns all executables
found in PATH that match the command name. If the option is /ad or
/d, which prints 'detail' information, i.e., date and file size.
When used with the 'WHICHDETAILS' environment variable, the details
options (/ad and /d) act as a toggle, disabling detailed output for
that execution. To cause which to print details by default, simply
'SET WHICHDETAILS=<value>', where <value> is anything you like. I
use '1', as it is a single byte and saves valuable environment space.
Feel free to use whatever you like, though; the only thing that's
needed to make WHICHDETAILS work is for it to show up in the
environment.
Typically, one would not specify the file extension of a command to
search for; doing so limits the search to that specific file name.
In such a limited search, it's possible that which would return the
name of an executable that is farther down the PATH than the actual
file that is being executed. For example, if you have TEST.COM,
TEST.EXE, and TEST.BAT all residing in the current directory, specifying
TEST.BAT on the command line would cause which to report that TEST.BAT
is being executed when, in fact, TEST.COM is the program being run. A
better way is to simply search for TEST unless you really need to
find an executable with a specific extension.
In keeping with the execution order used by DOS, which displays COM
files first, followed by EXE files, and then BAT files (for searches
that do not have the extension specified). which searches the current
directory before searching the directories defined in PATH. To take
into consideration that which may be used on operating systems other
than DOS -- or with command processors other than COMMAND.COM -- which
checks for a list of program extensions in the PATHEXT environment
variable. To use the PATHEXT environment variable, set the variable with
the extentions you intend to use, each extension separated by a semi-
colon. E.g.:
SET PATHEXT=.COM;.EXE;.BAT;.CMD;.VBS;.VBE;.JS;.JSE;.WSF;.WSH
If PATHEXT is not specified in the environment, which defaults to the
DOS-standard extensions of .COM, .EXE and .BAT. If PATHEXT is specified
in the environment, which searches in the order the extensions are
listed. If you're going to use this variable, be sure you understand
the execution order of the command processor you are using. The example
given above is taken from my own NT system -- with standard command
processor and VB Script, Java Script and Windows Scripting Host
installed. Your mileage may vary, so understand your command processor's
execution order before adding PATHEXT to the environment.
OPTIONS
which accepts the following options:
/? *
--help
Displays a short summary of how to use the program. When
this switch is in the first position on the command line,
which ignores all other command-line entries and displays
help information
/v *
--version
Displays version and licensing information. When this
switch is in the first position on the command line, which
ignores all other command-line entries and displays
version information
/a *
-a
Displays all executable files matching command that are
found in PATH, rather than just the first match. This
option cannot be used with other options
/ad *
-ad
Displays all executable files matching command that are
found in PATH, rather than just the first match. Includes
file size and date information for the executable. This
option cannot be used with other options
/d *
-d
Displays first executable file matching command that is
found in PATH. Includes file size and date information for
the executable. This option cannot be used with other
options
NOTE: which checks for the switchar defined in DOS. If you have set a
different switchar than the standard "/" character, which will
honour your preferred setting.
ENVIRONMENT VARIABLES
which uses the following environment variables:
PATH The list of directories to search for command
PATHEXT The list of program extensions to check (optional)
WHICHDETAILS Sets default behaviour to display file details (optional)
DIAGNOSTICS
Possible exit values are:
0 Success:
-- An executable file matching command was found
-- Help or version information was displayed
1 Failure due to the following:
-- A matching executable file could not be found
-- Invalid command-line option
NOTE
This command has no way of knowing about COMMAND.COM internal commands
and, therefore, is unable to help you resolve such conflicts. Under
DOS, COMMAND.COM executes internal commands before searching PATH to
find the executable being called.
If which is searching for multiple files and is able to locate one or
more files, the exit value will be 0 even if other commands are not
found. Only the first position on the command line is tested for
options; all other entries will be treated as filenames.
LIMITATIONS
Technically not a bug (rather, a limitation of a 16-bit, real-mode DOS
app), but which will not work correctly on partitions larger than 2 GB.
So, if you want to use which on non-DOS systems, make sure you're looking
for 8.3 filenames on a < 2GB partition with a PATH that doesn't contain
any spaces or other funky characters. In other words, it's a DOS app. If
you try to use which on, say, Windows Me with a 20-gig partition, you're
outta luck.
AUTHOR
Trane Francks <trane@gol.com>
I prefer being contacted via e-mail; however, you can snail-mail me at:
Trane Francks
Sento Hills Tsurukawa #305
1856-4 Kanai-cho, Machida City
Tokyo 195-0071
JAPAN
DOS Extensions 20 March 2002