Comment out file paths in a file matching lines in another file with sed and bash

Question

I have a file (names.txt) with the following content:

/bin/pgawk
/bin/zsh
/dev/cua0
/dev/initctl
/root/.Xresources
/root/.esd_auth

... and so on. I want to read this file line by line, and use sed to comment out matches in another file. I have the code below, but it does nothing:

#/bin/bash
while read line
do
        name=$line
        sed -e '/\<$name\>/s/^/#/' config.conf
done < names.txt

Lines in the input file needs to be commented out in config.conf file. Like follows:

config {
    #/bin/pgawk
    #/bin/zsh
    #/dev/cua0
    #/dev/initctl
    #/root/.Xresources
    #/root/.esd_auth
}

I don't want to do this by hand, because the file contains more then 300 file paths. Can someone help me to figure this out?

Answer 1

You need to use double quotes around your sed command, otherwise shell variables will not be expanded. Try this:

sed "/\<$name\>/s/^/#/" config.conf

However, I would recommend that you skip the bash for-loop entirely and do the whole thing in one go, using awk:

awk 'NR==FNR{a[$0];next}{for(i=1;i<=NF;++i)if($i in a)$i="#"$i}1' names.txt config.conf

The awk command stores all of the file names as keys in the array a and then loops through every word in each line of the config file, adding a "#" before the word if it is in the array. The 1 at the end means that every line is printed.

It is better not to use regular expression matching here, as some of the characters in your file names (such as . ) will be interpreted by the regular expression engine. This approach does a simple string match, which avoids the problem.