Advanced find and replace/prepend with sed

find_and_prepend.bash

#!/bin/bash

# these ideas was used during conversion from C code to C++

directory_whitelist="dir1 dir2" # directories to replace files in

for dir in $(directory_whitelist); do
  pushd $dir;
  # do replacement but use prefix to make sure replacement only happens once (in this case prepending std::)
  # \1 in the replace portion of the sed command is used to keep the character before the match (typically a space or '(')
  # otherwise that character will get overwritten with the replacement
  grep -rl --include={*.h,*.cpp} "[^std::]abs(" | xargs -i@ sed -i 's/\([^std::]\)abs(/\1std::abs(/g' @;
  popd;
done