Safely replace `backticks` with POSIX-style $(command substitutions) in scripts.

tickoff

#!/bin/sh # tickoff -- G.Nixon, 2013. Public Domain.

# Safely replace backticks with POSIX "$()" style command substitutions.
# Takes a shell script (from stdin, or as parameters) and replaces pairs of
# backticks with $(substitutions), per line. If a backtick is unmatched
# or escaped, returns an error with the offending line number.

case "$1" in *elp|-h) echo 'Usage: tickoff [script ...]'; echo
 echo ' Replace `backticks` with $(command substitutions).'; echo '
 Takes shell script (from stdin, or as parameters) and replaces pairs of
 backticks with $(substitutions), per line. If a backtick is unmatched
 or escaped, returns an error with the offending line number.'; exit 0 ;; *)

 t(){ sed 's/\`/\$\(/' ;}; tt(){ t|sed 's/\`/\)/' ;}; et(){ grep -lq '\\\`' ;}
 at(){ grep -lq \` ;}; dt(){ o="$(cat)"; if $(echo "$o" | et); then
  echo "Can't do escapes:" >&2; echo "$o" | grep -n '\\\`' >&2; return 1; fi
  while $(echo "$o" |t|at); do o="$(echo "$o" |tt|dt)"; done; echo "$o" ;}
  
 if [ x"$@" = x"" ]; then oo="$(dt)"; else oo="$(dt < "$@")"; fi
 if [ $? != 0 ]; then exit 1; fi; if $(echo "$oo" | grep -lq \`); then
  echo "Mismatched:" >&2; echo $(echo "$oo" | grep -n \`) >&2; exit 1; else
  echo "$oo"
 fi ;;
esac

For those unaware, see why you want to do this.