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How to search and replace variables in a file?
But I need to modify only the variables which are present in variable_list file and leave others as it is. The first sed expression escapes the $ which is a regex metacharacter. The second extracts just the variable name, then we use indirection to get the value in our current shell and use it in the sed expression.
How to replace a string in a shell script?
I am using the below code for replacing a string inside a shell script. but it’s getting replaced with $replace instead of the value of that variable. Could anybody tell what went wrong? If you want to interpret $replace, you should not use single quotes since they prevent variable substitution.
Is there a way to substitute a variable in a string?
Once inside, there’s nothing you can do to invoke variable substitution, until you leave. Use double quotes instead: you can still use single quotes, but you have to “open” them when you want the variable expanded at the right place. otherwise the string is taken “literally” (as @paxdiablo correctly stated, his answer is correct as well)
How to find the value of a variable in SED?
Note that your original version contains single quotes around the sed string, which doesn’t insert the value of $line. It is trying to look for the literal line after the end of the line $ (which will never find anything). Since you are looking for the value of the variable in $line, you need to do an eval to get this.
How to replace a variable in a Perl file?
If you happen to have Perl (but not gettext and envsubst) you can do the simple replacement with a short script: I assumed the variable names will only have uppercase letters and underscores, but the first pattern should be easy to alter as needed. $ENV {…} references the environment Perl sees.
Can you substitute an environment variable in PHP?
Similarly to the Perl answer, environment variable substitution can be delegated to the PHP CLI. Dependency on PHP may or may not be acceptable depending on the tech stack in use.
How to replace a string in a SED file?
You should be able to ‘cat’ the resin.conf file into sed, do the replacement, and redirect the output back to resin.conf, something like this: where ABC is a regular expression matching what you want to find, and XYZ is what you want to replace it with.