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.


Phil Hughes


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Thanks, this was helpful, the

Woody's picture

Thanks, this was helpful, the script did a good job ;)


.inc's picture

Hello there, great job but i use other way:

It includes using Zshell [ zsh ] an is as simple as:

zmv '(*)' '${(L)1}'

Have a good day.

Now we have convmv

Paulo Sedrez's picture

I have made my own scripts (tolower, toupper) back in the early 1990's, but now we have convmv:

convmv --lower --notest *

(note the --notest - the default is to show the actions instead of doing it)

It can also convert character sets, including - but not limited to - UTF-8 normalization forms C (Linux and many others) and D (Mac OS X).


MikeInMaine's picture

thanks, convmv works great

Better lowercase mousetrap

David Tangye's picture

For handling names with spaces, and not being limited to all of the current directory, use parameters, eg * or *.jpg or whatever, try:


while [ "$1" ] ; do
echo -ne "\n$f:"
if [ -f "$f" ]; then
echo -n "(file) "
lc=`echo $f | awk '{print(tolower($0));}'`
if [ "$lc" != "$f" ]; then
echo "-> '$lc'"
mv -i "$f" "$lc"

Have a C program to do something similar

Anonymous's picture


not much of a script writer myself, but I have something like this in a suit of shell utilities I wrote
hosted at:

also includes nifty tools for command line image processing - useful in conjunction with netpbm.

unfortunately, I don't use a lot of standard libraries and reimplemented things myself for learning purposes, but its all good.

Good information in the comments

Phil Hughes's picture

There is a lot of good information in the comments. Note that if I were to write the script today I would do it different. At the time (I don't know when I really wrote it--the date was a filesystem timestamp on an LS-120 disk I was reading so I am pretty sure it was written years before that--it was to convert MS-DOS file names to lower case. Thus, some of the concerns (such as a space in a filename) were just not considerations.

Phil Hughes

Next line works only for

Anonymous Beast's picture

Next line works only for english
lc=`echo $x | tr '[A-Z]' '[a-z]'`

Please use next line for real lowercase:
lc=`echo $x | awk '{print(tolower($0));}'`

another way

techno's picture

for i in *
mv -f "$i" `echo "$i" | tr A-Z a-z`

Slight improvement for extended chars...

Paul C's picture

Not sure if this will work for unicode but it should at least handle latin charset beyond the a-z range - change:

lc=`echo $x | tr '[A-Z]' '[a-z]'`


lc=`echo $x | tr "[:upper:]" "[:lower:]"`

Why not simply use rename ?

Simon Stroh's picture

Hi there ! =)
This can also be done easier with the "rename" tool that ships with perl:

rename 's/.*/-f&&lc||$_/e' *

well, shorter at least :-)

regards, Simon

lower case, use rename

brother.sand's picture

Alternatively, if your distro happens to include the "rename" command you can simply do this:

~$ rename 'y/A-Z/a-z/' *

That sets all files in the current directory to lower case. 'natch.



Anonymous's picture

If available on your system "rename" is also a very nice command. It is able to handle regular expressions. For example to lowercase all files ending with ".txt" you could use this one command:

rename 'y/A-Z/a-z/' *.txt

You can find more information on this page:
renaming multiple files

Bugs in this script

Anonymous's picture

This script will not perform correctly, and can even be dangerous to use, because it doesn't properly handle special characters in filenames. What if the filenames contain single quotes, or double quotes, or spaces, or asterisks, or combinations of such? An extreme case is when a file is called "* a"...

a safer version

dm's picture

nice script, however lines 8 and 12 are unsafe (will break for file names with embedded spaces... so it's kinda a bug ;-)

double square brackets test will always work:

[[ -f $fileName ]] && ...

if you prefer to stick to old 1998 test, wrap the test parameters in double quotation marks.

I used to have a little

Brent's picture

I used to have a little alias for the job using xargs, but now I just use:

rename 'y/A-Z/a-z/' *

Hi, Brent! That's cool!

Anonymous's picture

Hi, Brent! That's cool!

It's called Perl rename

Marin's picture

since it uses Perl regex to do the whole thing. Also, you can use this to rename files with some pattern -- that's why regex was created and I love it!

Here's a Python version that does a bit more

mde's picture

Not sure if you're just focused on the bash way to do this. I wrote something like this a while back in Python that I've found pretty useful, especially for music collections. It does some other name normalization, too.

Use of `ls`

Anonymous's picture

What advantage is there in using:

for x in `ls`


for x in *

There isn't an advantage, in

Anonymous's picture

There isn't an advantage, in fact it's more of a disadvantage due to bash's word splitting. It won't work if your filenames have spaces. See the following example:

$ touch "file-without-spaces" "file with spaces"
$ for i in *; do echo "--- $i ---"; done
--- file-without-spaces ---
--- file with spaces ---
$ for i in `ls`; do echo "--- $i ---"; done
--- file-without-spaces ---
--- file ---
--- with ---
--- spaces ---

I always change the IFS var

Anonymous's picture

I always change the IFS var when dealing with files with spaces


for FILES in $(find /some/dir)
echo $FILES

while read i

Dabe's picture

Personally I've grown accustomed to:

  /bin/ls | while read i; do
     blah blah "$i" | foo >> bar.out

My "smv" (sed + mv) bash function looks like:

function smv () {

   if [ "$#" -lt 2 ]; then
        echo "Usage: smv 's/pat/tern/'  [ ...]" 1>&2
        local pattern
        pattern="$1"; shift

        while [ "$#" -ge 1 ]; do
            new=`echo "$1" | sed -e "$pattern"`
            echo mv \"$1\" \"$new\"
            mv "$1" "$new"


None, however he's using sh,

Anonymous's picture

None, however he's using sh, not bash.

"for x in *" is is far better, as would using [['s be better, since he's not even quoting his variables.

Best still, he could just be using the tool rename, most distros have it available for installing.

My "tolower" Perl script

Reid's picture
#!/usr/bin/perl -s

if(@ARGV == 0) {
	opendir PWD, ".";
	@ARGV = readdir PWD;
	closedir PWD;

foreach (@ARGV) {
	# skip if no upper case!
	next unless /[[:upper:]]/;
	warn "# starting \"$_\"\n" if $v; # verbose mode
	next if $_ eq ".";
	next if $_ eq "..";
	next if m#.*/\.\.?$#;
	$pathname = $_;
	warn "# Doing \"$pathname\"\n" if $v; # verbose mode
	if($r && -d $_ && /^[^\/]+$/) {
		print "# visiting directory $_\n";
		opendir DIR, $_;
		my @dir = readdir DIR;
		closedir DIR;
		foreach my $entry (@dir) {
			next if $entry eq "..";
			next if $entry eq ".";
			warn "# Adding $_/$entry\n" if $v; # verbose mode
			unshift @ARGV, "$_/$entry";
		warn "# Redo-ing\n" if $v; # verbose mode
	if(($dir, $filename) = m!(.*/)(.*)!) {
		$_ = $filename;
	} else {
		$dir ="";
	# unicode-friendly way to do equivalent of English [A-Z] -> [a-z]
	print "mv $pathname $dir$_\n";
	unless($n) {
		if(-e "${dir}${xx}.$$") {
			# leave it there, increment xx
			if(-e "${dir}${xx}.$$") {
				die "\"${dir}${xx}.$$\" no longer safe. Quitting.\n";
		print "# moving \"$pathname\" to \"${dir}${xx}.$$\"\n" if $v; # verbose mode
		# rename twice in case of case-insensitive file systems
		rename($pathname, "${dir}${xx}.$$")
		|| print "# couldn't rename \"$pathname\" to \"${dir}${xx}.$$\": $!\n";
		print "# moving \"${dir}${xx}.$$\" to \"$dir$_\"\n" if $v; # verbose mode
		rename("${dir}${xx}.$$", "$dir$_")
		|| print "# couldn't rename \"${dir}${xx}.$$\" to \"$dir$_\": $!\n";


Many ways to do this:

PaulTTT's picture


rename 'y/A-Z/a-z/' *

is clearly the tersest, but there are other ways.