How to Find Default Shell of a User in a Shell Script

configurationshell

I was wondering if there's a way to find out the default shell of the current user within a shell script?

Use case: I am working on a script that sets an alias for a command and this alias is set within a shell script.

!# /bin/bash
alias = 'some command to set the alias'

There's a logic in the script where it tries to find the default shell of the user that executes the script and adds this alias in the respective ~/.bashrc or ~/.zshrc file

But as I am adding a shebang in the front of the script and explicitly asking it to use bash, answers posted here always return bash as expected although I am executing this script on a ZSH terminal.

Is there a way to get the shell type where the script is executed regardless of the shebang set?

I am looking for a solution that works on both Mac and all the linux based bistro.

Best Answer

$ finger $USER|grep -oP 'Shell: \K.*'
/bin/mksh

Related Solutions

Is Changing Root’s Default Shell a Bad Practice?

Yes. If system fails during booting you can log into root shell. If you have separate /usr some shells can fail to successfully start.

I'd advice to create account toor (uid 0, gid 0) with non-standard shell while left root with default shell.

Shell Script Timeout – Timing Out in a Shell Script

What about this:

foo=`{ { cat 1>&3; kill 0; } | { sleep 2; kill 0; } } 3>&1`

That is: run the output-producing command and sleep in the same process group, a process group just for them. Whichever command returns first kills the whole process group.

Would anyone wonder: Yes, the pipe is not used; it's bypassed using the redirections. The sole purpose of it is to have the shell run the two process in the same process group.

As Gilles pointed out in his comment, this won't work in a shell script because the script process would be killed along with the two subprocesses.

One way¹ to force a command to run in a separate process group is to start a new interactive shell:

#!/bin/sh
foo=`sh -ic '{ cat 1>&3; kill 0; } | { sleep 2; kill 0; }' 3>&1 2>/dev/null`
[ -n "$foo" ] && echo got: "$foo" || echo timeouted

But there might be caveats with this (e.g. when stdin is not a tty?). The stderr redirection is there to get rid of the "Terminated" message when the interactive shell is killed.

Tested with zsh,bash and dash. But what about oldies?

B98 suggests the following change, working on Mac OS X, with GNU bash 3.2.57, or Linux with dash:

foo=`sh -ic 'exec 3>&1 2>/dev/null; { cat 1>&3; kill 0; } | { sleep 2; kill 0; }'`

–
^{1. other than setsid which appears to be non-standard.}

Best Answer

Related Solutions

Is Changing Root’s Default Shell a Bad Practice?

Shell Script Timeout – Timing Out in a Shell Script

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