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sed: Rename files to lower case

 
 7.4 Rename Files to Lower Case
 ==============================
 
 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
 

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