Rename files to lower case (sed, a stream editor)

This is a pretty strange use of sed. We transform text, and transform it to be shell commands, then just feed them to shell. Don’t worry, even worse hacks are done when using sed; I have seen a script converting the output of date into a bc program!

The main body of this is the sed script, which remaps the name from lower to upper (or vice-versa) and even checks out if the remapped name is the same as the original name. Note how the script is parameterized using shell variables and proper quoting.

#! /bin/sh
# rename files to lower/upper case...
#
# usage:
#    move-to-lower *
#    move-to-upper *
# or
#    move-to-lower -R .
#    move-to-upper -R .
#

help()
{
        cat << eof
Usage: $0 [-n] [-r] [-h] files...

-n      do nothing, only see what would be done
-R      recursive (use find)
-h      this message
files   files to remap to lower case

Examples:
       $0 -n *        (see if everything is ok, then...)
       $0 *


       $0 -R .

eof
}

apply_cmd='sh'
finder='echo "$@" | tr " " "\n"'
files_only=

while :
do
    case "$1" in
        -n) apply_cmd='cat' ;;
        -R) finder='find "$@" -type f';;
        -h) help ; exit 1 ;;
        *) break ;;
    esac
    shift
done

if [ -z "$1" ]; then
        echo Usage: $0 [-h] [-n] [-r] files...
        exit 1
fi

LOWER='abcdefghijklmnopqrstuvwxyz'
UPPER='ABCDEFGHIJKLMNOPQRSTUVWXYZ'

case `basename $0` in
        *upper*) TO=$UPPER; FROM=$LOWER ;;
        *)       FROM=$UPPER; TO=$LOWER ;;
esac


eval $finder | sed -n '

# remove all trailing slashes
s/\/*$//

# add ./ if there is no path, only a filename
/\//! s/^/.\//

# save path+filename
h

# remove path
s/.*\///

# do conversion only on filename
y/'$FROM'/'$TO'/

# now line contains original path+file, while
# hold space contains the new filename
x

# add converted file name to line, which now contains
# path/file-name\nconverted-file-name
G

# check if converted file name is equal to original file name,
# if it is, do not print anything
/^.*\/\(.*\)\n\1/b

# escape special characters for the shell
s/["$`\\]/\\&/g

# now, transform path/fromfile\n, into
# mv path/fromfile path/tofile and print it
s/^\(.*\/\)\(.*\)\n\(.*\)$/mv "\1\2" "\1\3"/p


' | $apply_cmd

7.4 Rename Files to Lower Case