Convert Filenames to Lowercase

I was going to claim I wrote this yesterday but the timestamp on the file is 22 Nov 1998. Nothing new, nothing fancy but it does the job.

Back in the good old days, there was an operating system that didn't seem to think NAME and name were different. The result was that sometimes when you transfered files from a floppy disk (remember them?) created on that Dumb Old System, you would clutter your directory with uppercase filenames. As us UNIX old-timers learned a nifty trick to get directory names to sort before filenames in the output of the ls command (namely, start directory names with an uppercase letter), having filenames with uppercase letters was irritating.

After using the mv command all too many times and typing things like mv FILE.TXT file.txt, I wrote this script. I was thinking I could put a new coat of paint on it but, in reality, it does the job and is easy to understand. (The line numbers are there, of course, just for reference.)

    1   #!/bin/sh
    2   # lowerit
    3   # convert all file names in the current directory to lower case
    4   # only operates on plain files--does not change the name of directories
    5   # will ask for verification before overwriting an existing file
    6   for x in `ls`
    7     do
    8     if [ ! -f $x ]; then
    9       continue
   10       fi
   11     lc=`echo $x  | tr '[A-Z]' '[a-z]'`
   12     if [ $lc != $x ]; then
   13       mv -i $x $lc
   14     fi
   15     done

Line 6 starts a loop (which ends with line 15). The ls command returns a list of filenames which are sequentially assigned to the shell variable x. The if test (lines 8 through 10) checks to see if the current filename is that of a plain file. If not, the remainder of the statements in the current loop iteration are skipped.

If line 11 is to be executed we know that we have an ordinary file. Using tr we convert the filename to lowercase and assign the new name to the shell variable lc. Line 12 then checks to see if the lowercase version of the name differs from the original. If it does, line 13 is executed to change the name of the original file to the new lowercase name. The -i option causes the mv to prompt for confirmation if executing the command would overwrite an existing filename.