Linux Shell的第一个小程序

#!/bin/bash
# we have less than 3 arguments. Print the help text:
if [ $# -lt 3 ]; then
cat<<HELP
ren -- renames a number of files using sed regular expressions

USAGE: ren 'regexp' 'replacement' files
EXAMPLE: rename all *.HTM files in *.html:
ren 'HTM$' 'html' *.HTM

HELP
exit 0
fi
OLD="$1"
NEW="$2"
# The shift command removes one argument from the list of
# command line arguments.
shift
shift
# $* contains now all the files:
for file in $*; do
if [ -f "$file" ]; then
newfile=`echo "$file" | sed  "s/${OLD}/${NEW}/g"`
if [ -f "$newfile" ]; then
echo "ERROR: $newfile exists already"
else
echo "renaming $file to $newfile "
mv "$file" "$newfile"
fi
fi
done

./ren 'txt$' 'txt1' *.txt