#!/bin/bash
	#Usage $ rename4esp ext "RegExp" "Replacement_String"
	#will rename the names of all files extension "ext" by
        #substituting "RegExp" by "ReplacementString".
	#Note that "RegExp" is actually a real regular expression 
	#Of course it can accommodate a simple character sequence
# Example
# $ rename4esp dat " " "_" 
      # will rename files with extension "dat"
      # by substituting ALL blanks with underscores

ls -1 *."$1" | awk '{a=$0;gsub(/'"$2"/,\""$3"\"');print "mv","\""a"\"","\""$0"\""}'