Search and replace using the silver searcher and sed

ag-replace.sh

#!/usr/bin/env zsh

# Currently the script will choke on tilde characters used in either search or
# replace terms

# inspired by
# https://gist.github.com/hlissner/db74d23fc00bed81ff62
# https://gist.github.com/kates/5915285

# ag
# -0 --> Separate the filenames with \0, rather than \n: this allows 
#        xargs -0 <command> to correctly process filenames containing spaces 
#        or newlines.
# --files-with-matches --> Only print the names of files containing matches, 
#        not the matching lines. An empty query will print all files that 
#        would be searched.

# xargs
# -0 --> see ag description

# sed
# -r --> Use extended regular expressions rather than basic regular expressions
# -i replace in place, if followed by a suffix will create backup files
# -e --> execute the following command on any processed file

if [ $# -eq 3 ]; then
  ag -0 --files-with-matches $1 $3 | xargs -0 -I {} sed -i '' -e "s~$1~$2~g" {}
elif [ $# -eq 4 ]; then
  ag -0 --files-with-matches $1 $3 | xargs -0 -I {} sed -i.$4 -e "s~$1~$2~g" {}
elif [ $# -eq 2 ]; then
  ag -0 --files-with-matches $1 | xargs -0 -I {} sed -i '' -e "s~$1~$2~g" {}
else
  echo 'usage: $ ag-replace SEARCH_TERM REPLACE_TERM [PATH] [BACKUP_EXTENSION]'
  echo 'eg: $ ag-replace red green src'
fi