#!/bin/sh

_printhelp ()
{
    cat<<EOF
Usage: ${1##*/} [OPTIONS] SEARCH REPLACE [FILES]

Replace SEARCH by REPLACE in FILES. If no file is provided, use stdin.
Backslashes are interpreted in SEARCH and REPLACE (e.g. \n, \t). If you want to
inhibit this behaviour, you need to double them.

Options:

  -h:  Show this help.
  -i:  Replace file content instead of printing to stdout.

EOF
}

OPT_INPLACE=""
while getopts ":ih" opt; do
    case $opt in
        i)
            OPT_INPLACE=-i ;;
        h)
            _printhelp "$0"
            exit 1 ;;
        ?)
            _printhelp "$0"
            exit 1 ;;
    esac
done

shift $(($OPTIND - 1))

if [ $# -lt 2 ]; then
    _printhelp "$0"
    exit 1
fi

search="$1"
replace="$2"
shift 2

_replace()
{
    ## We cannot use gsub, otherwise regex substitutions could occur.
    ## Source: http://mywiki.wooledge.org/BashFAQ/021
    awk -v s="$search" -v r="$replace" 'BEGIN {l=length(s)} {o="";while (i=index($0, s)) {o=o substr($0,1,i-1) r; $0=substr($0,i+l)} print o $0}' "$@"
}

if [ $# -eq 0 ] || [ -z "$OPT_INPLACE" ]; then
    _replace "$@"
else
    for i ; do
        out="$(mktemp "$i.XXXXXX")"
        _replace "$i" > "$out"
        mv "$out" "$i"
    done
fi