How can I execute a shell-script in a Bash sub-shell?

Question

I have a shell-function that executes a command within a sub-shell, after setting some environment variables, e.g.

$ with-env-overrides git status

It's implemented using eval in a sub-shell

with-env-overrides() {
  (
    source $HOME/.env-overrides
    eval "$@"
  )
}

this means I can make use of aliases, and shell-functions, e.g.

$ with-env-overrides gs

but unfortunately, eval gets confused when arguments contain spaces, or shell meta-characters, e.g.

$ with-env-overrides grep "foo bar" /etc/passwd
grep: bar: No such file or directory

How can I achieve this without using eval, but without loosing the ability to use aliases etc?

Igor Chubin · Accepted Answer · 2013-06-05 02:28:14Z

2

You can do the same but without eval.

with-env-overrides() {
  (
    source $HOME/.env-overrides
    "$@"
  )
}

Example:

$ cat ~/.env-overrides 
export A=1000
$ export | grep ^A=
$ with-env-overrides export | ^grep A=
declare -x A="1000"

As you can see, in the second case, you've got an environment with the A variable.

answered Jun 5, 2013 at 2:28

Igor Chubin

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3 Comments

Samveen Over a year ago

Exactly what I would suggest.

Mike Williams Over a year ago

Hmm, unfortunately, I don't appear to be able to leverage aliases using that method.

rici Over a year ago

@MikeWilliams: That's correct. Aliases are very limited, and have a number of wierdnesses. One of them is that they act more like built-ins than commands, so you cannot quote them or construct them out of two strings, or expand a parameter to invoke one. Use shell functions instead.

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