#!/bin/bash

# "subst", ÆÄÀÏ¿¡¼­ ¾î¶² ÆÐÅÏÀ» ´Ù¸¥ ÆÐÅÏÀ¸·Î ¹Ù²ãÁÖ´Â ½ºÅ©¸³Æ®.
# Áï, "subst Smith Jones letter.txt".

ARGS=3
E_BADARGS=65   # ÇÊ¿äÇÑ ÀÎÀÚ°¡ ºüÁ®ÀÖÀ½.

if [ $# -ne "$ARGS" ]
# ½ºÅ©¸³Æ®·Î ³Ñ°ÜÁø ÀÎÀÚÀÇ °¹¼ö¸¦ È®ÀÎ(Ç×»ó ÀÌ·¸°Ô Çϼ¼¿ä).
then
  echo "»ç¿ë¹ý: `basename $0` old-pattern new-pattern filename"
  exit $E_BADARGS
fi

old_pattern=$1
new_pattern=$2

if [ -f "$3" ]
then
    file_name=$3
else
    echo "\"$3\" Àº ¾ø´Â ÆÄÀÏÀÔ´Ï´Ù."
    exit $E_BADARGS
fi

# ¿©±â°¡ °¡Àå Áß¿äÇÑ ºÎºÐÀÔ´Ï´Ù.
sed -e "s/$old_pattern/$new_pattern/g" $file_name
# 's'´Â sedÀÇ Ä¡È¯(substitution) ¸í·É¾îÀÌ°í,
# /pattern/ Àº ÁÖ¼Ò ¸ÅĪÀ» ½ÇÇà½Ãŵ´Ï´Ù.
#  Àü¿ª(global) Ç÷¡±×ÀÎ "g"¸¦ ¾²¸é ´ÜÁö ù¹ø° ÀÏÄ¡ÇÏ´Â $old_pattern¸¸ 
#+ ġȯ½ÃÅ°Áö ¾Ê°í °¢ ÁÙ¿¡¼­ ÀÏÄ¡ÇÏ´Â "¸ðµç" $old_patternÀ» ġȯ½Ãŵ´Ï´Ù.
# ´õ ÀÚ¼¼ÇÑ ¼³¸íÀº 'sed' ¹®¼­¸¦ Àо¼¼¿ä.

exit 0    # ½ºÅ©¸³Æ®ÀÇ ½ÇÇàÀÌ ¼º°øÀ̶ó¸é 0À» ¸®ÅÏ.