script: Am I running in bash or zsh?

spiralofhope · 05-15-2009, 09:44 PM

I've googled for answers, and I've also searched through this forum and I don't know the right search phrase to use for my question. I've also checked the zsh manual for a parameter which might give a hint, but no luck so far.

I have a script which I want to be able to run under many different scripting environments. I want it to be able to adapt appropriately to use the builtins for its shell.

So, for example there are some differences between bash and zsh

Code:

time=`ls -gG --full-time "$1" 2> /dev/null`

zsh:

Code:

echo "${time[12,30]}"

bash:

Code:

echo "${time:15:29}"

or

zsh:

Code:

setopt xtrace

bash:

Code:

set -x

So for my script to do the right thing, without making any assumptions about its environment, it needs to learn how it's been run.

I don't want to assume anything based on the names of the processes on the system, for example by using `kill` to determine if a process exists.

I don't want to rely on $SHELL, since if I start off in zsh and then I manually run `bash` .. $SHELL remains pointed at zsh! Maybe bash doesn't use $SHELL?

Is there some way to do this?

Disillusionist · 05-16-2009, 06:24 AM

How about:

Code:

ps -fp $$

EDIT:

or:

Code:

shell=`ps -o cmd --no-heading $$|cut -d' ' -f1`
echo $shell

synss · 05-16-2009, 04:37 PM

What about programing using POSIX? Any shell should understand POSIX. You can try POSIX compatibility with dash. At least, that is what I do…

The opposite solution if you insist on non-POSIX is to set the shebang right: if you want your script to run on bash

Code:

#!/bin/bash

if you want zsh

Code:

#!/bin/zsh

.

unSpawn · 05-16-2009, 07:04 PM

That 'ps' output only works correct if 'ps' is not an alias. Running 'readlink -f /proc/$$/exe' OTOH should work correctly. Builtins could be another way: of the shells I tested (Ash, Bash, Bsh, Jsh, Ksh, Tcsh) only Bash has internal "help" (as in something like 'help >/dev/null 2>&1 || echo "not bash?').

spiralofhope · 05-19-2009, 07:56 PM

Quote:

Originally Posted by Disillusionist

How about:

Code:

ps -fp $$

EDIT:

or:

Code:

shell=`ps -o cmd --no-heading $$|cut -d' ' -f1`
echo $shell

Aha, I knew there was a way.

Quote:

Originally Posted by unSpawn

That 'ps' output only works correct if 'ps' is not an alias.

I could run ps as "ps" or \ps to ensure that I bypass an alias/procedure.

Code:

echo `"ps" -o cmd --no-heading $$|"cut" -d' ' -f1`

Quote:

Originally Posted by unSpawn

Running 'readlink -f /proc/$$/exe' OTOH should work correctly.

Good one. I could do it like this:

Code:

"basename" `"readlink" -f /proc/$$/exe`

Or like this:

Code:

MYSHELL="$("basename" $("readlink" -f /proc/$$/exe))"

Quote:

Originally Posted by unSpawn

Builtins could be another way: of the shells I tested (Ash, Bash, Bsh, Jsh, Ksh, Tcsh) only Bash has internal "help" (as in something like 'help >/dev/null 2>&1 || echo "not bash?').

Code:

help >/dev/null 2>&1 || echo "not bash?"

That's pretty sneaky! It's a great way to avoid using external programs. I don't think I'll go for this because it's a sortof hackish undocumented thing to do, and it might not work in the future or for all shells.

Quote:

Originally Posted by synss

What about programing using POSIX?

While that's an interesting problem to solve, it's not important for me right now. I may need to rework a lot of the way I think in order to avoid the shell-specific stuff I've been doing, so it'll be something for me to work on later.

Quote:

Originally Posted by synss

The opposite solution if you insist on non-POSIX is to set the shebang right: if you want your script to run on bash

Code:

#!/bin/bash

if you want zsh

Code:

#!/bin/zsh

I cannot make an assumption as to what's available on their system, so this won't work for me.

archtoad6 · 06-14-2009, 04:54 PM

While I suspect that unSpawn's

Code:

readlink -f /proc/$$/exe

is the most reliable,

Code:

echo $SHELL

will work in bash; I'm curious to know what others it also works in.

spiralofhope · 06-14-2009, 11:36 PM

Quote:

Originally Posted by archtoad6

While I suspect that unSpawn's

Code:

readlink -f /proc/$$/exe

is the most reliable,

Code:

echo $SHELL

will work in bash; I'm curious to know what others it also works in.

That works in zsh too.