which - locate a command
which [-a] filename ...
which returns the pathnames of the files which would be executed in the
current environment, had its arguments been given as commands in a
strictly POSIX-conformant shell. It does this by searching the PATH
for executable files matching the names of the arguments.
-a print all matching pathnames of each argument
0 if all specified commands are found and executable
1 if one or more specified commands is nonexistent or not exe
2 if an invalid option is specified
Debian 12 Jul 2004 WHICH(1)