ファイル名を一括置換する

#!/bin/sh
#rep_filename.sh

. f_askdir.sh
. f_askstring.sh

ask_directory 1
if [ $? -eq 1 ]; then
    exit 1
fi
echo "Target directory is \"${_DIRNAME}\""

ask_string "Input Target Common Name: " 0
COMNAME1=$_STR
echo "Common Name is \"${COMNAME1}\""

ask_string "Input Replace Common Name: " 0
COMNAME2=$_STR
echo "Replace Common Name is \"${COMNAME2}\""

ask_string "Input Target Extension: " 0
EXTENSION=$_STR
echo "Target Extension is \"${EXTENSION}\""

CURRENTDIR=$(pwd)
cd $_DIRNAME

NUM=0
#対象ファイルの読み込み
for FNAME in *$COMNAME1*.$EXTENSION; do
    if [ -f "$FNAME" ]; then
        #拡張子以外の取り出し
        FNAME2=${FNAME%."$EXTENSION"}
        mv -b $FNAME $COMNAME2${FNAME2#"$COMNAME1"}.$EXTENSION
        NUM=$(expr $NUM + 1)
    fi
done

if [ $NUM -eq 0 ]; then
    echo "No file."
else
    echo "*** Successful."
fi

cd $CURRENTDIR
unset _DIRNAME EXTENSION COMNAME1 COMNAME2 CURRENTDIR FNAME FNAME2 _STR

$ ls
a1.text a2.text a3.text a4.text a5.text 

$ ./rep_filename.sh 
Input Directory (Blank is Cancel.) : .
Target directory is "."
Input Target Common Name: a
Common Name is "a"
Input Replace Common Name: b
Replace Common Name is "b"
Input Target Extension: text
Target Extension is "text"
*** Successful.

$ ls
b1.text b2.text b3.text b4.text b5.text