How to determine the current shell I'm working on
There are three approaches to finding the name of the current shell's executable:
Please note that all three approaches can be fooled if the executable of the shell is
/bin/sh
, but it's really a renamedbash
, for example (which frequently happens).Thus your second question of whether
ps
output will do is answered with "not always".echo $0
- will print the program name... which in the case of the shell is the actual shell.ps -ef | grep $$ | grep -v grep
- this will look for the current process ID in the list of running processes. Since the current process is the shell, it will be included.This is not 100% reliable, as you might have other processes whose
ps
listing includes the same number as shell's process ID, especially if that ID is a small number (for example, if the shell's PID is "5", you may find processes called "java5" or "perl5" in the samegrep
output!). This is the second problem with the "ps" approach, on top of not being able to rely on the shell name.echo $SHELL
- The path to the current shell is stored as theSHELL
variable for any shell. The caveat for this one is that if you launch a shell explicitly as a subprocess (for example, it's not your login shell), you will get your login shell's value instead. If that's a possibility, use theps
or$0
approach.
If, however, the executable doesn't match your actual shell (e.g.
/bin/sh
is actually bash or ksh), you need heuristics. Here are some environmental variables specific to various shells:$version
is set on tcsh$BASH
is set on bash$shell
(lowercase) is set to actual shell name in csh or tcsh$ZSH_NAME
is set on zshksh has
$PS3
and$PS4
set, whereas the normal Bourne shell (sh
) only has$PS1
and$PS2
set. This generally seems like the hardest to distinguish - the only difference in the entire set of environment variables betweensh
andksh
we have installed on Solaris boxen is$ERRNO
,$FCEDIT
,$LINENO
,$PPID
,$PS3
,$PS4
,$RANDOM
,$SECONDS
, and$TMOUT
.
ps -p $$
should work anywhere that the solutions involving ps -ef
and grep
do (on any Unix variant which supports POSIX options for ps
) and will not suffer from the false positives introduced by grepping for a sequence of digits which may appear elsewhere.
Try
ps -p $$ -oargs=
or
ps -p $$ -ocomm=