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As per my knowledge, to determine the current shell we use echo $0 in the shell. Rather I want my script to check in which shell it is running. So, I tried to print $0 in the script and it returns the name of the script as it should. So, my question is how can I find which shell is my script running in during runtime?

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what scripting language are you using? Also, worse case, you can always shell out a system command to get the "echo $0" results inside of the script. –  BriGuy Apr 4 '13 at 5:45
    
echo $0 is not an option here ,as the script will run on many different machines where first thing I'll need to check is the shell. –  g4ur4v Apr 4 '13 at 5:55
    
So what is the scripting language then? –  BriGuy Apr 4 '13 at 5:58
    
@BriGuy: It's a unix shell script. –  g4ur4v Apr 4 '13 at 6:01
2  
Well, if you add #! /bin/sh - at the top, it will run in sh. Do you mean what variant of sh is it? –  Stéphane Chazelas Apr 4 '13 at 6:58

7 Answers 7

up vote 10 down vote accepted

On linux you can use /proc/PID/exe.

Example:

# readlink /proc/$$/exe
/bin/zsh
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3  
That's a bit too specific for me (e.g. on Debian it prints zsh4 or ksh93). /bin/sed -r -e 's/\x0.*//' /proc/$$/cmdline gives zsh or ksh instead. (That'd be $0 if shells didn't magically fix this to give the scripts name instead). –  frostschutz Apr 12 '13 at 23:17
    
@frostschutz Yours is the best answer, run for the +500! –  Teresa e Junior Apr 14 '13 at 16:05
    
Not really. It depends on what the OP really wants. Not reading the link also causes #!/bin/sh to return just sh even if it's really bash, dash, etc. Can't follow links and not follow links at the same time. Unless you check if it's sh and follow then or something, but that solution is plain weird. –  frostschutz Apr 14 '13 at 17:00
1  
This suffers from the dreaded All the world's a Linux box disease. /proc is as ugly and unportable as it gets. –  Jens Apr 15 '13 at 12:58
4  
@Jens that's why I specified this applies to Linux only. /proc is not 'ugly'. /proc is often a very elegant solution. Unportable yes, but because something is unportable doesn't make it ugly. –  Patrick Apr 16 '13 at 12:17

Maybe not what you're asking for, but this should work to some extent to identify the interpreter currently interpreting it for a few like Thomson (osh), Bourne, Bourne-again, Korn, Z, (T)C, Policy-compliant Ordinary, Yet Another, rc, akanga, es shells, wish, tclsh, expect, perl, python, ruby, php, JavaScript (SpiderMonkey shell and JSPL at least), MS/Wine cmd.exe, command.com (MSDOS, FreeDOS...).

'echo' +"'[{<?php echo chr(13)?>php <?php echo PHP_VERSION.chr(10);exit;?>}\
@GOTO DOS [exit[set 1 [[set 2 package] names];set 3 Tcl\ [info patchlevel];\
if {[lsearch -exact $1 Expect]>=0} {puts expect\ [$2 require Expect]\ ($3)} \
elseif {[lsearch -exact $1 Tk]>=0} {puts wish\ ($3,\ Tk\ [$2 require Tk])} \
else {puts $3}]]]' >/dev/null ' {\">/dev/null \
">"/dev/null" +"\'";q="#{",1//2,"}";a=+1;q='''=.q,';q=%!\"
'echo' + /*>/dev/null
echo ">/dev/null;status=0;@ {status=1};*=(" '$' ");~ $status 1&&{e='"\
"';eval catch $2 ^'&version {eval ''echo <='^ $2 ^'&version''}';exit};e='"\
"';if (eval '{let ''a^~a''} >[2] /dev/null'){e='"\
"';exec echo akanga};eval exec echo rc $2 ^ version;\" > /dev/null
: #;echo possibly pre-Bourne UNIX V1-6 shell;exit
if { bindkey >& /dev/null } then
exec echo $version
else
exec echo csh
endif
:DOS
@CLS
@IF NOT "%DOSEMU_VERSION%"=="" ECHO DOSEMU %DOSEMU_VERSION%
@ECHO %OS% %COMSPEC%
@VER
@GOTO FIN
", unless eval 'printf "perl %vd\n",$^V;exit;'> "/dev/null";eval ': "\'';
=S"';f=false e=exec\ echo n=/dev/null v=SH_VERSION;`(eval "f() { echo :
};f")2>$n` $f||$e Bourne-like shell without function
case `(: ${_z_?1}) 2>&1` in 1) $e ash/BSD sh;;esac;t(){
eval "\${$1$v+:} $f &&exec echo ${2}sh \$$1$v";};t BA ba;t Z z;t PO po;t YA ya
case `(typeset -Z2 b=0;$e $b)2>$n` in 00) (eval ':${.}')2>$n&&eval '
$e ksh93 ${.sh.version}';t K pdk;$e ksh88;;esac;case `(eval '$e ${f#*s}$($e 1
)$((1+1))')2>$n` in e12)$e POSIX shell;;esac;$e Bourne-like shell;: !
print "ruby ",RUBY_VERSION,"\n";exit;' ''';import sys
print("python "+sys.version);z='''*/1;s="";j="JavaScript";print((f="function")
==(t=typeof version)?"string"==typeof(v=version())?v:(typeof build!=f?"":s=
"SpiderMonkey ")+j+" "+v:(t=="undefined"?j+"?":version)+"\n");if(s)build();/*
:FIN } *///'''

I posted the initial version of that which_interpreter script circa 2004 on usenet. Sven Mascheck has a (probably more useful to you) script called whatshell that focuses on identifying Bourne-like shells. You can also find a merged version of our two scripts there.

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2  
This cannot identify Python 3, only Python 2. To fix that, change print to be a function. –  Chris Down Apr 4 '13 at 9:19
20  
This is the biggest WTF moment of the year so far. +1 for taking portability past sanity. –  l0b0 Apr 4 '13 at 11:35
    
Thanks @ChrisDown. Should be fixed now. –  Stéphane Chazelas Apr 4 '13 at 12:52
    
It would be nice if it would recognize fish shell. –  xfix Mar 23 at 16:39
    
@xfix, I remember trying even before adding php and javascript but couldn't find a solution then. The complexity grows exponentially with the number of languages to support (as everything you add must be valid (or at least have unnoticeable side-effects) in all the supported languages) so it would be even more difficult now. I'm not saying it's impossible but that would probably mean dropping support for some other languages. –  Stéphane Chazelas Mar 23 at 20:45

This is what I use in my .profile to check for various shells on the systems I work on. It doesn't make fine distinctions between ksh88 and ksh93, but it has never failed me.

Note that it doesn't require a single fork or pipe.

# Determine what (Bourne compatible) shell we are running under. Put the result
# in $PROFILE_SHELL (not $SHELL) so further code can depend on the shell type.

if test -n "$ZSH_VERSION"; then
  PROFILE_SHELL=zsh
elif test -n "$BASH_VERSION"; then
  PROFILE_SHELL=bash
elif test -n "$KSH_VERSION"; then
  PROFILE_SHELL=ksh
elif test -n "$FCEDIT"; then
  PROFILE_SHELL=ksh
elif test -n "$PS3"; then
  PROFILE_SHELL=unknown
else
  PROFILE_SHELL=sh
fi
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Note that only very recent versions of ksh93 have $KSH_VERSION. That variable comes from pdksh and never made it to AT&T ksh88. –  Stéphane Chazelas Apr 15 '13 at 21:28
    
Right, which is why I have the second test for FCEDIT. –  Jens Apr 16 '13 at 6:12
1  
Right. Note that posh (pdksh with most non-POSIX features removed so you would probably want to call it "sh") has no FCEDIT nor KSH_VERSION but has PS3 (maybe not for long), though it's unlikely for one to have it as a login shell. Also note that the code above wouldn't reflect whether bash or zsh are in sh emulation mode, which may be a problem if you're using $PROFILE_SHELL to decide whether or not to enable this or that feature. See also Sven Mascheck's whatshell for more you may (or may not) want to check. –  Stéphane Chazelas Apr 16 '13 at 6:25

You could try

ps -o args= -p "$$"

which will give you the name of the command associated with the script's pid.

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Doesn't work when using a shebang as far as I can tell. sprunge.us/QeHD –  Chris Down Apr 4 '13 at 9:20
    
Sorry, @ChrisDown, Flup. My bad, I had incorrectly translated cmd to comm when POSIXifying the answer. –  Stéphane Chazelas Apr 4 '13 at 11:04
    
@StephaneChazelas Ah, cool, thanks. –  Chris Down Apr 4 '13 at 12:09

You can use the command:

$ echo $SHELL

to find out the shell from within the script.

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12  
No. $SHELL is the shell of choice of the user. Initialised from the login shell of the user. Nothing to do with the currently running shell. –  Stéphane Chazelas Apr 4 '13 at 6:55

If there is the lsof command available on your system, you can get the full path of the parent shell executable by getting the parent PID via ps and parsing the ouput of lsof -p $ppid (see How to determine the current shell i'm working on?).

#!/bin/sh
ppid="`ps -p "$$" -o ppid=`"
lsof -nP -p "$ppid" | awk 'NR==3 {print $NF; exit}'
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On my system this returns /, if I use NR==4 I get the path to the shells parent. –  Thor Apr 15 '13 at 7:10

Outside of Linux land or lacking access to the /proc filesystem or equivelent, you can make use of pstree:

Assuming you have the pid of

On a Mac:

./test.sh 
16012
-+= 00001 root /sbin/launchd
 \-+= 00245 wingwong /sbin/launchd
   \-+= 04670 wingwong /Applications/Utilities/Terminal.app/Contents/MacOS/Terminal -psn_0_2052597
     \-+= 11816 root login -pf wingwong
       \-+= 11817 wingwong -bash
         \-+= 16012 wingwong ksh ./test.sh
           \-+- 16013 wingwong pstree -p 16012

On a Linux box:

./test.sh 
14981
bash(14981)---pstree(14982)

The format and style of the output from pstree differs, depending on your environment, but you can enforce ASCII output and then sed/tr/awk/etc. filter the output to get the shell that is running the script.

So a cleaned up output version(works for Mac or Linux OS runs):

#!/usr/bin/env sh
pstree  -p $$  | tr ' ()' '\012\012\012' | grep -i "sh$" | grep -v "$0" | tail -1

On run yields:

./test.sh 
sh

And when run with a different shell:

#!/usr/bin/env ksh
pstree  -p $$  | tr ' ()' '\012\012\012' | grep -i "sh$" | grep -v "$0" | tail -1

Yields:

./test.sh 
ksh

No root or special filesystem required. Note, my filtering assumes that the shell binary name ends with sh and that there are no intermediate entries which end with sh. Also assumes that you didn't name your script "sh" or some unfortunate grep pattern that will obliterate information. :) Will require some customization for your own environment to ensure a higher degree of foolproofing.

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