sudo bash -c gave permission denied

Question

In my linux (centos 7), there are 2 users A (normal user) and B (belongs to wheel group). I am trying to change User A's .bash_profile file by running the following command with user B.

./test.sh /home/a/.bash_profile "export something"

#!/bin/bash

set -o errexit

filePath=${1};
content=${2};

result=`sudo grep "$content" $filePath || true`\
if [[ -z $result ]] || [[ $result == \#* ]]; then
    echo "inside the first if";
    sudo sh -c "$(sed '$a\' ${filePath} > ${filePath}.bak)";
    sudo sh -c "$(echo $content >> ${filePath}.bak)";
    sudo rm -fr ${filePath};
    sudo mv ${filePath}.bak ${filePath};
fi

However it gave the following error:

/home/a/.bash_profile.bak: Permission denied

Answer 1

You don't need $() operator in sudo sh -c ... commands.

When you use this operator for sed '$a\' ${filePath} > ${filePath}.bak then sed and redirection to file > commands are first executed under user b rights, which are insufficient for writing. And only after that sudo sh -c is performed upon the output of the previous commands.

Use sudo sh -c "sed ...", and sudo sh -c "echo ..." instead.