How to determine the current shell i'm working on ?

Question

How to determine the current shell i am working on ?

Does ps command output will alone do ?

How to do this in different flavors of UNIX ?

Answer 1

1) There are 3 approaches:

• echo $0 - will print the program name... which in the case of shell is the actual shell

• ps -ef|grep $$|grep -v grep - will look for current process ID in teh list of running processes. Current process being shell, it will inlcude shell.

  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 #.

  It also has the same problem as the other 2 approaches - it can be fooled if the executable of the shell is /bin/sh but it's really a renamed bash, for example. So those 2 issues answer your second question of whether ps output will do.

• echo $SHELL The path to the current shell is in SHELL variable for any shell. The caveat for the last one is that if you launch a shell explicitly as a subprocess (e.g. it's not your login shell) you will get you login shell's value instead - if that's a possibility, use the ps or $0 approach.

2) However, if the executable is not matching real 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 zsh

• ksh has $PS3 and $PS4 set, whereas normal Bourne shell (sh) only has $PS1 and $PS2 set. This generally seems like the hardest to distinguish - the ONLY difference in entire set of envionmental variables between sh and ksh we have installed on Solaris boxen is $ERRNO, $FCEDIT, $LINENO, $PPID, $PS3, $PS4, $RANDOM, $SECONDS, $TMOUT.

Answer 2

Try echo $SHELL.

Answer 3

You can try:

ps | grep `echo $$` | awk '{ print $4 }'

Or:

echo $SHELL

Answer 4

ps is the most reliable method. The SHELL envar is not guaranteed to be set and even if it is, it can be easily spoofed

Answer 5

echo $$ # Gives the Parent Process ID 
ps -ef | grep $$ | awk '{print $8}' #use the PID to see what the process is.

from http://www.unix.com/unix-dummies-questions-answers/10390-how-do-you-know-what-your-current-shell.html

Answer 6

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.

Answer 7

On Mac OS X (& FreeBSD):

ps -p $$ -axco command | sed -n '$p'