which - locate a command
which [-a] filename ...
which returns the pathnames of the files (or links) 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. It does not follow symbolic links.
-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 executable
2 if an invalid option is specified