Bash script is not inheriting its parent’s env

bashshellshell-script

An alternative title for this question would be:

"command recognized in parent shell is not found in subshell"

I have this in a parent shell

source ~/.quicklock/ql.sh

and this command is recognized in my current shell:

ql_acquire_lock

then I run a script like so:

./script/tsc.sh

in that script we have:

#!/usr/bin/env bash
set -e;
ql_acquire_lock

I must be very confused about how shells work, because I thought a child shell/process would inherit the env of the parent, unless explicitly calling unset etc.?

Here is the error I get:

./scripts/tsc.sh: line 3: ql_acquire_lock: command not found

Best Answer

A child shell will inherit the environment of the parent shell.

The environment will contain what is exported by the parent shell.

If your shell function is not exported, it will not exist in the child's environment.

A bash shell function may be exported for use in a bash child shell using

export -f functionname

in the parent shell.

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Bash – automatically load shell scripts from /usr/bin

The alias you have defined will only take effect once the alias command is actually called. Thus if you were to do this:

$ source myscript
$ e "Hello"

It should work. However, this is clearly not ideal since you want e to be available whenever you start bash. Luckily, bash provides a number of ways to automatically run commands when the shell is started. For the full details of how bash starts up, see the manual page. For our purposes, it is enough to know that ~/.bashrc (that is, a file named ".bashrc" in your home directory) is run as your shell starts up. One way to make your alias available at startup would be to add this line at the end of ~/.bashrc:

source myscript

However, if you were to do this for every alias you wanted, your /usr/bin folder would likely become a mess. And, if you are on a multi-user system, filling /usr/bin/ with scripts like this may cause other users problems as well. Thus, it is better to place your aliases right inside .bashrc and forgo the separate script all together. Since you are using Ubuntu, inside your .bashrc file you probably have something that looks like this:

if [ -f ~/.bash_aliases ]; then
. ~/.bash_aliases 
fi

This code looks for a file call .bash_aliases in your home directory and runs anything it finds in that file as well. If you have this, or if you add this code to your .bashrc, you could also put your alias in ~/.bash_aliases. This provides an easy way to keep all your aliases in one place and keep your .bashrc file uncluttered.

Bash – Run a script on multiple shells

It would probably be easier to have two separate versions of the script. Since it is short it may not be worth adding extra code to handle the differences between the two formats as jw013 suggested. On the other hand if you had a larger script it would probably be easier to have one and make the script execute different commands depending on where it is running from.

Best Answer

Related Solutions

Bash – automatically load shell scripts from /usr/bin

Bash – Run a script on multiple shells

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