Replace string in a file from bash script value

Question

This bash script runs on a Mac terminal, it needs to ask the user for input $name, then replace a string in another file to include the user input PLACEHOLDER_BACKEND_NAME=$name.

#!/bin/bash
read -r name

if ! grep -q PLACEHOLDER_BACKEND_NAME="\"$name\"" ~/path-to-file.sh; then
perl -pi -e 's/PLACEHOLDER_BACKEND_NAME.*/PLACEHOLDER_BACKEND_NAME=$name/g' ~/psth-to-file.sh
fi

The perl replace command fail to take in the value in the $name variable. I am not familiar with Bash.

Answer 1

bash doesn't expand the variable content inside a single quote string. You have to use double quoted strings.

Examples :

This will print : my name is : $name

name="haha"
echo 'my name is : $name'

This will print : my name is : haha

name="haha"
echo "my name is : $name"

So just replace

perl -pi -e 's/PLACEHOLDER_BACKEND_NAME.*/PLACEHOLDER_BACKEND_NAME=$name/g' ~/psth-to-file.sh

with

perl -pi -e "s/PLACEHOLDER_BACKEND_NAME.*/PLACEHOLDER_BACKEND_NAME=$name/g" ~/psth-to-file.sh

Answer 2

Variables are not expanded within single-quotes. The $name variable is within single-quotes. You can fix that by breaking out of the single-quotes in the middle:

perl -pi -e 's/PLACEHOLDER_BACKEND_NAME.*/PLACEHOLDER_BACKEND_NAME='"$name"'/g' ~/psth-to-file.sh

Notice that I double quoted the variable, to protect from globbing and word splitting.