Set environment variable by reference in a function

Question

I'm trying to write a bash function to init some environment variables. I want to append a path to them unless it is already there.

I'd call it like

$ add_to_path /home/brucewayne MYENV

This is what I have so far.

# adds $1 to path $2 (e.g. add '/opt/blabla' to $PYTHONPATH)
add_to_path() {
    if [ -d "$1" ] && [[ ":${!2}:" != *":$1:"* ]]; then
        $2="$1:${!2}"
    fi
}

but when I run it, I get

./a.sh: line 6: MYENV=/home/brucewayne:/home/pal: No such file or directory

My guess is that $2="$1:${!2}" is not being interpreted as an assignment. $2 should become MYENV and the value should be set to MYENV but, instead, it looks like I can't set the value by reference. What would be a correct way of doing this in bash?

anubhava · Accepted Answer · 2014-02-20 10:17:35Z

2

Add export in your function:

add_to_path() {
    if [ -d "$1" ] && [[ ":${!2}:" != *":$1:"* ]]; then
       export $2="$1:${!2}"
    fi
}

answered Feb 20, 2014 at 10:17

anubhava

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2 Comments

Eduard Gamonal Over a year ago

damn it I had tried that but with a different right side and failed. thanks! it does work

AsymLabs Over a year ago

You can make it a bit cleaner by using: [[ -d "$1" && ":${!2}:" != ":$1:" ]] && export $2="$1:${!2}". The if .. then .. fi construct would no longer be needed.

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