Shell Programming and Scripting

echo 1_234sd.txt | awk -F "_" '{printf "%03d_%s\n",$1,$2}'
echo 23_234sd.txt |  awk -F "_" '{printf "%03d_%s\n",$1,$2}'

#!/bin/ksh93

ls *_234sd.txt |
while read FILENAME
do
   IFS="_" typeset -a aFilename=($FILENAME)
   IFS="" NEWFILENAME=$(printf "%03d_%s" ${aFilename[0]} ${aFilename[1]})
   echo "$FILENAME --> $NEWFILENAME"
   #mv $FILENAME $NEWFILENAME
done