Bash: Checking for string-substring

Question

Following this answer in superuser, I have wrote that function in bash:

_add_env()
{
    export $1
    if [[ ":\$$1:" != *":$2:"* ]]; then
            eval $1="\$$1:$2";
    fi
};

I'm calling it that way: _merge_env PATH "/home/subway/land"

It seems that the condition is true even though PATH contains the given path.

Here is the relevant bash -x output:

What am I doing wrong?

choroba · Accepted Answer · 2013-01-07 13:54:38Z

1

"\$$1" is not evaluated to the content of $PATH, but to $PATH. Use variable indirection:

[[ ":${!1}:" != *":$2:" ]]

answered Jan 7, 2013 at 13:54

choroba

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2 Comments

It works! Thanks. Would you mind to explain what does variable indirection mean? I mean, what exactly is its job?

Its jobs is what you try here: to use a value of a variable as a name of variable to expand.