w64devkit/man/man1/which.1

.TH WHICH 1 2026-10-20 "w64devkit" "w64devkit Manual"
.SH NAME
which \- locate commands in PATH
.SH SYNOPSIS
.B which
.RB [ \-a ]
.IR command ...
.SH DESCRIPTION
.B which
prints where each
.I command
is found.
It searches the directories of
.B PATH
in order and prints the first executable file that matches, or with
.B \-a
every match, one path per line.
A command that is not found prints nothing.
At least one
.I command
is required.
.SS Commands
A
.I command
that contains a slash or a backslash, or begins with a drive letter and
a colon, as in
.B ./tool
or
.BR C:tool ,
is a path, and
.B PATH
is not searched.
The path is tested as it stands, and then as described under
.BR "Executable files" ,
relative to the current directory when it is relative.
If no file matches, and the directory part is exactly
.IR /bin ,
.IR /usr/bin ,
.IR /sbin ,
or
.IR /usr/sbin ,
the last component is looked up as a command instead, so that
.B /bin/sh
finds a program named
.B sh
in
.BR PATH .
.SS Executable files
A match is a file, not a directory, that busybox considers executable.
That is a file whose name ends in
.BR .com ,
.BR .exe ,
.BR .sh ,
.BR .bat ,
or
.BR .cmd ,
in any case.
It is also a file of at least 4 bytes with any other name, except one
ending in
.BR .dll ,
that begins with
.B #!\&
or is a Windows program, a PE image that is not a DLL.
A cloud placeholder, such as an online-only OneDrive file, is judged by
its name alone.
.PP
In each directory
.B which
tries the command as given, then with
.BR .com ,
.BR .exe ,
.BR .sh ,
.BR .bat ,
and
.B .cmd
appended, in that order.
Only the first match in a directory is reported.
No suffix is appended to a command that already ends in one of these
suffixes, in any case, or in a period.
.B PATHEXT
is not consulted.
.SS PATH
.B PATH
is a list of directories separated by semicolons.
A directory may be written with slashes or backslashes, and one trailing
separator is ignored.
An empty element, as from a leading or doubled semicolon, stands for the
current directory.
The current directory is not searched otherwise.
When
.B PATH
is unset, the directories are
.I C:/Windows/System32
and
.IR C:/Windows .
.PP
busybox drops a single trailing semicolon from
.B PATH
when it starts in a Windows environment, as from
.BR cmd.exe .
A
.B PATH
set afterward, as in the kit's shell, keeps it, and then it ends with an
empty element.
.SS Output
Each line is the directory as written in
.BR PATH ,
less one trailing separator, a slash, and the command with the suffix
that matched, if one was added.
The path is not made absolute or canonical: a relative element gives a
relative path, and an empty element gives the command alone.
The command keeps the case in which it was typed, and an added suffix is
lowercase, whatever the case of the file's name.
A command that is a path is printed as given, with a suffix added if
needed.
Every backslash is printed as a slash.
.SS Applets in the shell
The kit's shell runs an applet itself, without searching
.BR PATH ,
when a command names one.
When the shell runs
.B which
under that name,
.B which
also reports applets, and its message for an unknown option begins with
.B Which:
instead of
.BR which: .
A command that names an applet is printed as the name alone, with no
directory, except
.BR busybox ,
which is printed as the path of
.IR busybox.exe .
A name with a suffix, such as
.BR ls.exe ,
is a file, not an applet.
.PP
With
.BR \-a ,
the matches in
.B PATH
follow the applet.
Without
.BR \-a ,
the first applet ends the search for every remaining command, so
.B which ls cat
prints only
.BR ls .
The exit status counts only the commands before that one.
.PP
A path such as
.B /bin/ls
that matches no file, and whose last component names an applet, is
printed as that component alone, even for
.BR busybox .
It does not end the search, and
.B PATH
is not searched for it, even with
.BR \-a .
.PP
Started any other way, as from
.BR cmd.exe ,
as
.B /bin/which
or
.B busybox which
in the shell, or by
.B env
or
.BR xargs ,
.B which
searches
.B PATH
alone.
It does so too when the shell runs it with standard input, output, or
error closed, as in
.BR "which ls 2>&\-" .
.SH OPTIONS
Options are recognized anywhere on the command line, so
.B which ls \-a
is the same as
.BR "which \-a ls" ,
unless
.B POSIXLY_CORRECT
is set.
.B \-\-
ends the options.
.TP
.B \-a
Print every match of each command, not only the first.
Every element of
.B PATH
is searched, and a directory that is listed twice is reported twice.
.TP
.B \-\-help
Print a usage message on standard output and exit with status 0.
It is recognized only as the first argument, and any further arguments
are then ignored.
.SH ENVIRONMENT
.TP
.B BB_GLOBBING
Unless it is
.BR 0 ,
the C runtime expands wildcards in the arguments when
.B which
starts, as needed when run from
.BR cmd.exe .
A busybox process started with it unset sets it to
.B 0
for its children, so commands run from the kit's shell receive their
operands as the shell expanded them.
.TP
.B BB_OVERRIDE_APPLETS
Read when the kit's shell runs
.BR which :
an applet that it tells the shell not to use is not reported as an
applet.
The value is described in
.BR busybox (1).
.TP
.BR LC_ALL ", " LC_CTYPE ", " LANG
If the first of these that is set has the value
.BR C ,
output to a console is not converted, as described in
.BR NOTES ,
and the console interprets the bytes in its own code page.
.TP
.B PATH
The directories to search, as described above.
.TP
.B POSIXLY_CORRECT
When set, the first
.I command
ends the options, so that later arguments such as
.B \-a
are commands.
.PP
Variables that affect every busybox applet, such as
.B BB_TERMINAL_MODE
for console output, are described in
.BR busybox (1).
.SH EXIT STATUS
.TP
.B 0
Every command searched for was found.
.TP
.B 1
A command was not found, no command was given, or an option was
unknown.
For the last two, a usage message is printed on standard error.
A command that is not found gets no message.
.TP
.B 141
Standard output is a pipe whose reader has exited, detected only when
the output fills a buffer before
.B which
finishes.
No message is printed.
.SH EXAMPLES
Find a program:
.PP
.RS 4
.EX
$ which gcc
C:/w64devkit/bin/gcc.exe
.EE
.RE
.PP
In the kit's shell, show both the applet and the program file of a
command, in the order the shell prefers them:
.PP
.RS 4
.EX
$ which \-a ls
ls
C:/w64devkit/bin/ls.exe
.EE
.RE
.PP
Test for a program in a script:
.PP
.RS 4
.EX
$ which ninja >/dev/null || echo ninja not found
.EE
.RE
.PP
Show which file a path names, since a suffix may be added:
.PP
.RS 4
.EX
$ which ./build
\&./build.sh
.EE
.RE
.PP
Search the current directory before the directories of
.BR PATH ,
as
.B cmd.exe
does:
.PP
.RS 4
.EX
$ PATH=";$PATH" which tool
tool.exe
.EE
.RE
.SH NOTES
Differences from a Unix
.BR which :
.IP \(bu 2
The only options are
.B \-a
and
.BR \-\-help .
.IP \(bu 2
A file is executable by its name or its first bytes, since Windows has no
execute permission.
.IP \(bu 2
Suffixes are appended to commands, and
.B PATHEXT
is ignored.
.IP \(bu 2
Output uses forward slashes, and
.B PATH
is separated by semicolons.
.IP \(bu 2
In the kit's shell, applets are reported, and a command after an applet
may be skipped.
.PP
Unlike
.B cmd.exe
and
.BR where.exe ,
.B which
does not search the current directory first.
The shell's
.B type
and
.B command \-v
also report builtins and functions, which
.B which
does not.
.PP
On Windows 10 version 1903 and later,
.I command
and
.B PATH
may contain any Unicode characters.
On older versions they are limited to the ANSI code page, and in a
double-byte code page, such as Shift JIS, the second byte of a character
may be taken for a backslash.
.PP
Lines end with LF, not CRLF.
When standard output is a console, the result is converted for display
from the ANSI code page, which is UTF-8 on Windows 10 version 1903 and
later.
An error writing standard output gives no message and, except as
described for status 141, does not change the exit status.
.SH SEE ALSO
.BR busybox (1),
.BR sh (1)