Posted By: Anonymous
How can I determine the current shell I am working on?
Would the output of the
ps command alone be sufficient?
How can this be done in different flavors of Unix?
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 renamed
bash, for example (which frequently happens).
Thus your second question of whether
psoutput 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
pslisting 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 same
grepoutput!). 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 the
SHELLvariable 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 the
If, however, the executable doesn’t match your actual shell (e.g.
/bin/shis actually bash or ksh), you need heuristics. Here are some environmental variables specific to various shells:
$versionis set on tcsh
$BASHis set on bash
$shell(lowercase) is set to actual shell name in csh or tcsh
$ZSH_NAMEis set on zsh
$PS4set, whereas the normal Bourne shell (
sh) only has
$PS2set. This generally seems like the hardest to distinguish – the only difference in the entire set of environment variables between
kshwe have installed on Solaris boxen is