Regex containing variable when regex comparison

Question

I want to write a bash script that takes an input string and if it doesn't contain a particular tag in the beginning, add the tag to the beginning. The following is the script I wrote

#! /bin/bash

message=$1

tag="hello"

filter="^$tag.*"

if [[ ! $message =~ $filter ]]; then
   message="$tag $message"
fi

echo $message

This works well as long as the tag doesn't contain a regular expression specific keyword.

For example if the tag was set to [hello] the filter doesn't work since the square bracket is a keyword.

How to change the filter so that it ignores any keywords containing in the tag?

How are you running the script?

Inian
– Inian

2017-02-02 06:30:30 +00:00
Commented Feb 2, 2017 at 6:30 — Inian
– Inian, Commented Feb 2, 2017 at 6:30

Benjamin W. · Accepted Answer · 2017-02-02 06:31:45Z

1

You can use shell patterns instead of regular expressions and quote them to avoid interpretation of meta characters:

if [[ $message != "$tag"* ]]; then
    message="$tag $message"
fi

answered Feb 2, 2017 at 6:31

Benjamin W.

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