ファイル内のアルファベットをすべて小文字にする

#!/bin/sh
#2small_char.sh

. f_askfname.sh
. f_askstring.sh

ask_filename "Target File ( Blank is Cancel. ) : " 1
if [ $? -ne 0 ]; then
    echo "*** Canceled."
    return 1
fi
FILE=${_STR}
echo "Target File is \"${FILE}\""

ask_string "Save File[ ${FILE}.small ] : " 1
if [ $? -ne 0 ]; then
    FILE2="${FILE}.small"
else
    FILE2=${_STR}
fi
echo "Save File is \"${FILE2}\""

#trコマンドの引数を逆にすれば
cat ${FILE} | tr '[A-Z]' '[a-z]' > ${FILE2}
echo "*** Successfull."
unset FILE1 FILE2 _STR

$ cat 1.txt
ABCDEFGHIJKLMNOPQRSTUVWXYZ

$ ./2small_char.sh 
Target File ( Blank is Cancel. ) : 1.txt
Target File is "1.txt"
Save File[ 1.txt.small ] : 
Save File is "1.txt.small"
*** Successfull.

$ cat 1.txt.small
abcdefghijklmnopqrstuvwxyz