which, whence

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© November 2003 Tony Lawrence
2003/11/12

Search PATH for a program:

$ which ls
/bin/ls
 

The original Bourne shell (sh) had no command like which. The csh introduced "which". Ksh uses "whence", and bash etc. will use "which".

If the thing being searched for is a shell builtin like "cd", "which" and "whence" won't find it, but how that is reported can be very different:

( ksh on SCO OSR5 )
$ whence cd
cd
( bash on Mac OS X)
$ which cd
no cd in /bin /sbin /usr/bin /usr/sbin /Users/apl/bin /usr/local/bin /Developer/Tools
( tcsh on Mac OS X)
% which cd
cd: shell built-in command.
 

You may also have a "whereis" command, though this usually only searches the "standard" directories: it probably won't look anywhere you might have added to your PATH.

On OSR5 and some other POSIX compliant platforms, /bin/cd and other common shell builtins exist, so you must call the actual binary if that's what you need.

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