I have large number of files in the format x00000.jpg, X00000.jpg and xx00000.jpg.
How can I rename these files so they are all uppercase, ignoring the numeric part of the name?
for f in * ; do mv -- "$f" "$(tr [:lower:] [:upper:] <<< "$f")" ; done
You can't rename files from Bash only, because Bash doesn't have any built-in command for renaming files. You have to use at least one external command for that.
If Perl is allowed:
perl -e 'for(#ARGV){rename$_,uc}' *.jpg
If Python is allowed:
python -c 'import os, sys; [os.rename(a, a.upper()) for a in sys.argv[1:]]' *.jpg
If you have thousands or more files, the solutions above are fast, and the solutions below are noticably slower.
If AWK, ls and mv are allowed:
# Insecure if the filenames contain an apostrophe or newline!
eval "$(ls -- *.jpg | awk '{print"mv -- \x27"$0"\x27 \x27"toupper($0)"\x27"}')"
If you have a lots of file, the solutions above don't work, because *.jpg expands to a too long argument list (error: Argument list too long).
If tr and mv are allowed, then see damienfrancois' answer.
If mv is allowed:
for file in *; do mv -- "$file" "${file^^}"; done
Please note that these rename .jpg to .JPG at the end, but you can modify them to avoid that.
The bash shell has a syntax for translating a variable name to all-caps.
for file in * ; do # or *.jpg, or x*.jpg, or whatever
mv "$file" "${file^^}"
done
This feature was introduced in bash version 4.0, so first verify that your version of bash implements it. To avoid mistakes, try it once replacing mv by echo mv, just to make sure it's going to do what you want.
The documentation for this feature is here, or type info bash and search for "upper".
You should probably decide what to do if the target file already exists (say, if both x00000.jpg and X00000.JPG already exists), unless you're certain it's not an issue. To detect such name collisions, you can try:
ls *.txt | tr '[a-z]' '[A-Z]' | sort | uniq -c | sort -n
and look for any lines not starting with 1.
rename
Probably the easiest way for renaming multiple files is using Perl's rename. To translate lowercase names to upper, you'd:
rename 'y/a-z/A-Z/' *
If the files are also in subdirs you can use globstar or find:
find . -maxdepth 1 -type f -iname "*.jpg" -execdir rename "y/a-z/A-Z/" {} +
References
Howto: Linux Rename Multiple Files At a Shell Prompt – nixCraft
More info about y/, translate instead of substitute.
DistroTube - Tools For Renaming Files In Linux
Combining previous answers could yield:
for file in * ; do # or *.jpg, or x*.jpg, or whatever
basename=$(tr '[:lower:]' '[:upper:]' <<< "${file%.*}")
newname="$basename.${file#*.}"
mv "$file" "$newname"
done
Using tr:
f="x00000.jpg"
n="${f%.*}"
n=$(tr '[:lower:]' '[:upper:]' <<< "$n")
f="$n.${f#*.}"
echo "$f"
OUTPUT:
X00000.jpg
if you are using the zsh like me:
for f in * ; do mv -- "$f" "${f:u}" ; done
If only renaming files/dirs is all you want, then you can use rnm :
rnm -rs '/./\C/g' -fo -dp -1 *
Explanation:
-rs : replace string. /./\C/g replaces all match of . (regex) to it's uppercase.
-fo : file only mode
-dp : depth of directory (-1 means unlimited).
More examples can be found here.
Rename all source files to uppercase and stage to git
#!/bin/bash
SOURCE_DIRS=('./src' './Public' './Private')
FILE_EXTENSION="*.php"
for dir in $SOURCE_DIRS; do
files="$(find "$dir" -name "${FILE_EXTENSION[#]}";)"
for file in $files; do
base_name="$(basename $file)";
new_name=$(sed "s/$base_name/${base_name^}/g" <<< $file)
git mv $file ${new_name} # or
# mv $file ${new_name}
done
done
#!/bin/bash
#script to loop through directories to merge files
mydir=/data/
files="/data/*"
for f in $files
do
if[ -d "$f" ]
then
for ff in $f/*
do
echo "Processing $ff"
done
else
echo "Processing $f"
fi
done
I have the above code to go through directories and sub-directories and list all the files. I am getting the error: syntax error near unexpected token `then'
What am I doing wrong here?
if [ -d "$f" ]
^
There needs to be a space between if and [. If you don't have a space, bash thinks you're trying to execute a command named if[.
files="/data/*"
for f in $files
Also know that this won't work. To store a wildcard expansion in a variable like that you need to use an array. The syntax is a bit hairier...
files=(/data/*)
for f in "${files[#]}"
Or you could write the wildcard inline the way you do with the inner loop. That would work fine.
for f in "$mydir"/*
For what it's worth, you could use find to recurse through all files and sub-directories recursively.
find /data/ -type f -print0 | while read -d $'\0' file; do
echo "Processing $file"
done
-type f matches files only. -print0 combined with -d $'\0' is a way to be extra careful with file names containing characters like spaces, tabs, and even newlines. It is legal to have these characters in file names so I like to write my scripts in a way that can handle them.
Note that this will recurse deeper than just sub-directories. It'll go all the way down. If that's not what you want, add -maxdepth 2.
As an alternative, you could probably replace this entire loop with something like
# find all files either in /data or /data/subdir
find /data -type f -maxdepth 2 | while read file; do
echo $file;
end
Here's a function that does what you ask, you pass it a folder see the call at the bottom func_process_folder_set "/folder".
# --- -------------------------------- --- #
# FUNC: Process a folder of files
# --- -------------------------------- --- #
func_process_folder_set(){
FOLDER="${1}"
while read -rd $'\0' file; do
fileext=${file##*.} # -- get the .ext of file
case ${fileext,,} # -- make ext lowercase for checking in case statement
echo "FILE: $file" # -- print the file (always use " " to handle file spaces)
done < <(find ${FOLDER} -type f -maxdepth 20 -name '*.*' -print0)
}
# -- call the function above with this:
func_process_folder_set "/some/folder"
I am writing a script in bash on Linux and need to go through all subdirectory names in a given directory. How can I loop through these directories (and skip regular files)?
For example:
the given directory is /tmp/
it has the following subdirectories: /tmp/A, /tmp/B, /tmp/C
I want to retrieve A, B, C.
All answers so far use find, so here's one with just the shell. No need for external tools in your case:
for dir in /tmp/*/ # list directories in the form "/tmp/dirname/"
do
dir=${dir%*/} # remove the trailing "/"
echo "${dir##*/}" # print everything after the final "/"
done
cd /tmp
find . -maxdepth 1 -mindepth 1 -type d -printf '%f\n'
A short explanation:
find finds files (quite obviously)
. is the current directory, which after the cd is /tmp (IMHO this is more flexible than having /tmp directly in the find command. You have only one place, the cd, to change, if you want more actions to take place in this folder)
-maxdepth 1 and -mindepth 1 make sure that find only looks in the current directory and doesn't include . itself in the result
-type d looks only for directories
-printf '%f\n prints only the found folder's name (plus a newline) for each hit.
Et voilà!
You can loop through all directories including hidden directrories (beginning with a dot) with:
for file in */ .*/ ; do echo "$file is a directory"; done
note: using the list */ .*/ works in zsh only if there exist at least one hidden directory in the folder. In bash it will show also . and ..
Another possibility for bash to include hidden directories would be to use:
shopt -s dotglob;
for file in */ ; do echo "$file is a directory"; done
If you want to exclude symlinks:
for file in */ ; do
if [[ -d "$file" && ! -L "$file" ]]; then
echo "$file is a directory";
fi;
done
To output only the trailing directory name (A,B,C as questioned) in each solution use this within the loops:
file="${file%/}" # strip trailing slash
file="${file##*/}" # strip path and leading slash
echo "$file is the directoryname without slashes"
Example (this also works with directories which contains spaces):
mkdir /tmp/A /tmp/B /tmp/C "/tmp/ dir with spaces"
for file in /tmp/*/ ; do file="${file%/}"; echo "${file##*/}"; done
Works with directories which contains spaces
Inspired by Sorpigal
while IFS= read -d $'\0' -r file ; do
echo $file; ls $file ;
done < <(find /path/to/dir/ -mindepth 1 -maxdepth 1 -type d -print0)
Original post (Does not work with spaces)
Inspired by Boldewyn: Example of loop with find command.
for D in $(find /path/to/dir/ -mindepth 1 -maxdepth 1 -type d) ; do
echo $D ;
done
find . -mindepth 1 -maxdepth 1 -type d -printf "%P\n"
The technique I use most often is find | xargs. For example, if you want to make every file in this directory and all of its subdirectories world-readable, you can do:
find . -type f -print0 | xargs -0 chmod go+r
find . -type d -print0 | xargs -0 chmod go+rx
The -print0 option terminates with a NULL character instead of a space. The -0 option splits its input the same way. So this is the combination to use on files with spaces.
You can picture this chain of commands as taking every line output by find and sticking it on the end of a chmod command.
If the command you want to run as its argument in the middle instead of on the end, you have to be a bit creative. For instance, I needed to change into every subdirectory and run the command latemk -c. So I used (from Wikipedia):
find . -type d -depth 1 -print0 | \
xargs -0 sh -c 'for dir; do pushd "$dir" && latexmk -c && popd; done' fnord
This has the effect of for dir $(subdirs); do stuff; done, but is safe for directories with spaces in their names. Also, the separate calls to stuff are made in the same shell, which is why in my command we have to return back to the current directory with popd.
a minimal bash loop you can build off of (based off ghostdog74 answer)
for dir in directory/*
do
echo ${dir}
done
to zip a whole bunch of files by directory
for dir in directory/*
do
zip -r ${dir##*/} ${dir}
done
If you want to execute multiple commands in a for loop, you can save the result of find with mapfile (bash >= 4) as a variable and go through the array with ${dirlist[#]}. It also works with directories containing spaces.
The find command is based on the answer by Boldewyn. Further information about the find command can be found there.
IFS=""
mapfile -t dirlist < <( find . -maxdepth 1 -mindepth 1 -type d -printf '%f\n' )
for dir in ${dirlist[#]}; do
echo ">${dir}<"
# more commands can go here ...
done
TL;DR:
(cd /tmp; for d in */; do echo "${d%/}"; done)
Explanation.
There's no need to use external programs. What you need is a shell globbing pattern. To avoid the need of removing /tmp afterward, I'm running it in a subshell, which may or not be suitable for your purposes.
Shell globbing patterns in a nutshell:
* Match any non-empty string any number of times.
? Match exactly one character.
[...] Matches with a character from between the brackets. You can also specify ranges ([a-z], [A-F0-9], etc.) or classes ([:digit:], [:alpha:], etc.).
[^...] Match one of the characters not between the braces.
* If no file names match the pattern, the shell will return the pattern unchanged. Any character or string that is not one of the above represents itself.
Consequently, the pattern */ will match any file name that ends with a /. A trailing / in a file name unambiguously identifies a directory.
The last bit is removing the trailing slash, which is achieved with the variable substitution ${var%PATTERN}, which removes the shortest matching pattern from the end of the string contained in var, and where PATTERN is any valid globbing pattern. So we write ${d%/}, meaning we want to remove the trailing slash from the string represented by d.
find . -type d -maxdepth 1
In short, put the results of find into an array and iterate the array and do what you want. Not the quickest but more organized thinking.
#!/bin/bash
cd /tmp
declare -a results=(`find -type d`)
#Iterate the results
for path in ${results[#]}
do
echo "Your path is $path"
#Do something with the path..
if [[ $path =~ "/A" ]]; then
echo $path | awk -F / '{print $NF}'
#prints A
elif [[ $path =~ "/B" ]]; then
echo $path | awk -F / '{print $NF}'
#Prints B
elif [[ $path =~ "/C" ]]; then
echo $path | awk -F / '{print $NF}'
#Prints C
fi
done
This can be reduced to find -type d | grep "/A" | awk -F / '{print $NF}' prints A
find -type d | grep "/B" | awk -F / '{print $NF}' prints B
find -type d | grep "/C" | awk -F / '{print $NF}' prints C
I have to rename a complete folder tree recursively so that no uppercase letter appears anywhere (it's C++ source code, but that shouldn't matter).
Bonus points for ignoring CVS and Subversion version control files/folders. The preferred way would be a shell script, since a shell should be available on any Linux box.
There were some valid arguments about details of the file renaming.
I think files with the same lowercase names should be overwritten; it's the user's problem. When checked out on a case-ignoring file system, it would overwrite the first one with the latter, too.
I would consider A-Z characters and transform them to a-z, everything else is just calling for problems (at least with source code).
The script would be needed to run a build on a Linux system, so I think changes to CVS or Subversion version control files should be omitted. After all, it's just a scratch checkout. Maybe an "export" is more appropriate.
Smaller still I quite like:
rename 'y/A-Z/a-z/' *
On case insensitive filesystems such as OS X's HFS+, you will want to add the -f flag:
rename -f 'y/A-Z/a-z/' *
A concise version using the "rename" command:
find my_root_dir -depth -exec rename 's/(.*)\/([^\/]*)/$1\/\L$2/' {} \;
This avoids problems with directories being renamed before files and trying to move files into non-existing directories (e.g. "A/A" into "a/a").
Or, a more verbose version without using "rename".
for SRC in `find my_root_dir -depth`
do
DST=`dirname "${SRC}"`/`basename "${SRC}" | tr '[A-Z]' '[a-z]'`
if [ "${SRC}" != "${DST}" ]
then
[ ! -e "${DST}" ] && mv -T "${SRC}" "${DST}" || echo "${SRC} was not renamed"
fi
done
P.S.
The latter allows more flexibility with the move command (for example, "svn mv").
for f in `find`; do mv -v "$f" "`echo $f | tr '[A-Z]' '[a-z]'`"; done
Just simply try the following if you don't need to care about efficiency.
zip -r foo.zip foo/*
unzip -LL foo.zip
One can simply use the following which is less complicated:
rename 'y/A-Z/a-z/' *
This works on CentOS/Red Hat Linux or other distributions without the rename Perl script:
for i in $( ls | grep [A-Z] ); do mv -i "$i" "`echo $i | tr 'A-Z' 'a-z'`"; done
Source: Rename all file names from uppercase to lowercase characters
(In some distributions the default rename command comes from util-linux, and that is a different, incompatible tool.)
This works if you already have or set up the rename command (e.g. through brew install in Mac):
rename --lower-case --force somedir/*
The simplest approach I found on Mac OS X was to use the rename package from http://plasmasturm.org/code/rename/:
brew install rename
rename --force --lower-case --nows *
--force Rename even when a file with the destination name already exists.
--lower-case Convert file names to all lower case.
--nows Replace all sequences of whitespace in the filename with single underscore characters.
Most of the answers above are dangerous, because they do not deal with names containing odd characters. Your safest bet for this kind of thing is to use find's -print0 option, which will terminate filenames with ASCII NUL instead of \n.
Here is a script, which only alter files and not directory names so as not to confuse find:
find . -type f -print0 | xargs -0n 1 bash -c \
's=$(dirname "$0")/$(basename "$0");
d=$(dirname "$0")/$(basename "$0"|tr "[A-Z]" "[a-z]"); mv -f "$s" "$d"'
I tested it, and it works with filenames containing spaces, all kinds of quotes, etc. This is important because if you run, as root, one of those other scripts on a tree that includes the file created by
touch \;\ echo\ hacker::0:0:hacker:\$\'\057\'root:\$\'\057\'bin\$\'\057\'bash
... well guess what ...
Here's my suboptimal solution, using a Bash shell script:
#!/bin/bash
# First, rename all folders
for f in `find . -depth ! -name CVS -type d`; do
g=`dirname "$f"`/`basename "$f" | tr '[A-Z]' '[a-z]'`
if [ "xxx$f" != "xxx$g" ]; then
echo "Renaming folder $f"
mv -f "$f" "$g"
fi
done
# Now, rename all files
for f in `find . ! -type d`; do
g=`dirname "$f"`/`basename "$f" | tr '[A-Z]' '[a-z]'`
if [ "xxx$f" != "xxx$g" ]; then
echo "Renaming file $f"
mv -f "$f" "$g"
fi
done
Folders are all renamed correctly, and mv isn't asking questions when permissions don't match, and CVS folders are not renamed (CVS control files inside that folder are still renamed, unfortunately).
Since "find -depth" and "find | sort -r" both return the folder list in a usable order for renaming, I preferred using "-depth" for searching folders.
One-liner:
for F in K*; do NEWNAME=$(echo "$F" | tr '[:upper:]' '[:lower:]'); mv "$F" "$NEWNAME"; done
Or even:
for F in K*; do mv "$F" "${F,,}"; done
Note that this will convert only files/directories starting with letter K, so adjust accordingly.
The original question asked for ignoring SVN and CVS directories, which can be done by adding -prune to the find command. E.g to ignore CVS:
find . -name CVS -prune -o -exec mv '{}' `echo {} | tr '[A-Z]' '[a-z]'` \; -print
[edit] I tried this out, and embedding the lower-case translation inside the find didn't work for reasons I don't actually understand. So, amend this to:
$> cat > tolower
#!/bin/bash
mv $1 `echo $1 | tr '[:upper:]' '[:lower:]'`
^D
$> chmod u+x tolower
$> find . -name CVS -prune -o -exec tolower '{}' \;
Ian
Not portable, Zsh only, but pretty concise.
First, make sure zmv is loaded.
autoload -U zmv
Also, make sure extendedglob is on:
setopt extendedglob
Then use:
zmv '(**/)(*)~CVS~**/CVS' '${1}${(L)2}'
To recursively lowercase files and directories where the name is not CVS.
Using Larry Wall's filename fixer:
$op = shift or die $help;
chomp(#ARGV = <STDIN>) unless #ARGV;
for (#ARGV) {
$was = $_;
eval $op;
die $# if $#;
rename($was,$_) unless $was eq $_;
}
It's as simple as
find | fix 'tr/A-Z/a-z/'
(where fix is of course the script above)
for f in `find -depth`; do mv ${f} ${f,,} ; done
find -depth prints each file and directory, with a directory's contents printed before the directory itself. ${f,,} lowercases the file name.
This works nicely on macOS too:
ruby -e "Dir['*'].each { |p| File.rename(p, p.downcase) }"
This is a small shell script that does what you requested:
root_directory="${1?-please specify parent directory}"
do_it () {
awk '{ lc= tolower($0); if (lc != $0) print "mv \"" $0 "\" \"" lc "\"" }' | sh
}
# first the folders
find "$root_directory" -depth -type d | do_it
find "$root_directory" ! -type d | do_it
Note the -depth action in the first find.
Use typeset:
typeset -l new # Always lowercase
find $topPoint | # Not using xargs to make this more readable
while read old
do new="$old" # $new is a lowercase version of $old
mv "$old" "$new" # Quotes for those annoying embedded spaces
done
On Windows, emulations, like Git Bash, may fail because Windows isn't case-sensitive under the hood. For those, add a step that mv's the file to another name first, like "$old.tmp", and then to $new.
With MacOS,
Install the rename package,
brew install rename
Use,
find . -iname "*.py" -type f | xargs -I% rename -c -f "%"
This command find all the files with a *.py extension and converts the filenames to lower case.
`f` - forces a rename
For example,
$ find . -iname "*.py" -type f
./sample/Sample_File.py
./sample_file.py
$ find . -iname "*.py" -type f | xargs -I% rename -c -f "%"
$ find . -iname "*.py" -type f
./sample/sample_file.py
./sample_file.py
Lengthy But "Works With No Surprises & No Installations"
This script handles filenames with spaces, quotes, other unusual characters and Unicode, works on case insensitive filesystems and most Unix-y environments that have bash and awk installed (i.e. almost all). It also reports collisions if any (leaving the filename in uppercase) and of course renames both files & directories and works recursively. Finally it's highly adaptable: you can tweak the find command to target the files/dirs you wish and you can tweak awk to do other name manipulations. Note that by "handles Unicode" I mean that it will indeed convert their case (not ignore them like answers that use tr).
# adapt the following command _IF_ you want to deal with specific files/dirs
find . -depth -mindepth 1 -exec bash -c '
for file do
# adapt the awk command if you wish to rename to something other than lowercase
newname=$(dirname "$file")/$(basename "$file" | awk "{print tolower(\$0)}")
if [ "$file" != "$newname" ] ; then
# the extra step with the temp filename is for case-insensitive filesystems
if [ ! -e "$newname" ] && [ ! -e "$newname.lcrnm.tmp" ] ; then
mv -T "$file" "$newname.lcrnm.tmp" && mv -T "$newname.lcrnm.tmp" "$newname"
else
echo "ERROR: Name already exists: $newname"
fi
fi
done
' sh {} +
References
My script is based on these excellent answers:
https://unix.stackexchange.com/questions/9496/looping-through-files-with-spaces-in-the-names
How to convert a string to lower case in Bash?
In OS X, mv -f shows "same file" error, so I rename twice:
for i in `find . -name "*" -type f |grep -e "[A-Z]"`; do j=`echo $i | tr '[A-Z]' '[a-z]' | sed s/\-1$//`; mv $i $i-1; mv $i-1 $j; done
I needed to do this on a Cygwin setup on Windows 7 and found that I got syntax errors with the suggestions from above that I tried (though I may have missed a working option). However, this solution straight from Ubuntu forums worked out of the can :-)
ls | while read upName; do loName=`echo "${upName}" | tr '[:upper:]' '[:lower:]'`; mv "$upName" "$loName"; done
(NB: I had previously replaced whitespace with underscores using:
for f in *\ *; do mv "$f" "${f// /_}"; done
)
Slugify Rename (regex)
It is not exactly what the OP asked for, but what I was hoping to find on this page:
A "slugify" version for renaming files so they are similar to URLs (i.e. only include alphanumeric, dots, and dashes):
rename "s/[^a-zA-Z0-9\.]+/-/g" filename
I would reach for Python in this situation, to avoid optimistically assuming paths without spaces or slashes. I've also found that python2 tends to be installed in more places than rename.
#!/usr/bin/env python2
import sys, os
def rename_dir(directory):
print('DEBUG: rename('+directory+')')
# Rename current directory if needed
os.rename(directory, directory.lower())
directory = directory.lower()
# Rename children
for fn in os.listdir(directory):
path = os.path.join(directory, fn)
os.rename(path, path.lower())
path = path.lower()
# Rename children within, if this child is a directory
if os.path.isdir(path):
rename_dir(path)
# Run program, using the first argument passed to this Python script as the name of the folder
rename_dir(sys.argv[1])
If you use Arch Linux, you can install rename) package from AUR that provides the renamexm command as /usr/bin/renamexm executable and a manual page along with it.
It is a really powerful tool to quickly rename files and directories.
Convert to lowercase
rename -l Developers.mp3 # or --lowcase
Convert to UPPER case
rename -u developers.mp3 # or --upcase, long option
Other options
-R --recursive # directory and its children
-t --test # Dry run, output but don't rename
-o --owner # Change file owner as well to user specified
-v --verbose # Output what file is renamed and its new name
-s/str/str2 # Substitute string on pattern
--yes # Confirm all actions
You can fetch the sample Developers.mp3 file from here, if needed ;)
None of the solutions here worked for me because I was on a system that didn't have access to the perl rename script, plus some of the files included spaces. However, I found a variant that works:
find . -depth -exec sh -c '
t=${0%/*}/$(printf %s "${0##*/}" | tr "[:upper:]" "[:lower:]");
[ "$t" = "$0" ] || mv -i "$0" "$t"
' {} \;
Credit goes to "Gilles 'SO- stop being evil'", see this answer on the similar question "change entire directory tree to lower-case names" on the Unix & Linux StackExchange.
I believe the one-liners can be simplified:
for f in **/*; do mv "$f" "${f:l}"; done
( find YOURDIR -type d | sort -r;
find yourdir -type f ) |
grep -v /CVS | grep -v /SVN |
while read f; do mv -v $f `echo $f | tr '[A-Z]' '[a-z]'`; done
First rename the directories bottom up sort -r (where -depth is not available), then the files.
Then grep -v /CVS instead of find ...-prune because it's simpler.
For large directories, for f in ... can overflow some shell buffers.
Use find ... | while read to avoid that.
And yes, this will clobber files which differ only in case...
find . -depth -name '*[A-Z]*'|sed -n 's/\(.*\/\)\(.*\)/mv -n -v -T \1\2 \1\L\2/p'|sh
I haven't tried the more elaborate scripts mentioned here, but none of the single commandline versions worked for me on my Synology NAS. rename is not available, and many of the variations of find fail because it seems to stick to the older name of the already renamed path (eg, if it finds ./FOO followed by ./FOO/BAR, renaming ./FOO to ./foo will still continue to list ./FOO/BAR even though that path is no longer valid). Above command worked for me without any issues.
What follows is an explanation of each part of the command:
find . -depth -name '*[A-Z]*'
This will find any file from the current directory (change . to whatever directory you want to process), using a depth-first search (eg., it will list ./foo/bar before ./foo), but only for files that contain an uppercase character. The -name filter only applies to the base file name, not the full path. So this will list ./FOO/BAR but not ./FOO/bar. This is ok, as we don't want to rename ./FOO/bar. We want to rename ./FOO though, but that one is listed later on (this is why -depth is important).
This comand in itself is particularly useful to finding the files that you want to rename in the first place. Use this after the complete rename command to search for files that still haven't been replaced because of file name collisions or errors.
sed -n 's/\(.*\/\)\(.*\)/mv -n -v -T \1\2 \1\L\2/p'
This part reads the files outputted by find and formats them in a mv command using a regular expression. The -n option stops sed from printing the input, and the p command in the search-and-replace regex outputs the replaced text.
The regex itself consists of two captures: the part up until the last / (which is the directory of the file), and the filename itself. The directory is left intact, but the filename is transformed to lowercase. So, if find outputs ./FOO/BAR, it will become mv -n -v -T ./FOO/BAR ./FOO/bar. The -n option of mv makes sure existing lowercase files are not overwritten. The -v option makes mv output every change that it makes (or doesn't make - if ./FOO/bar already exists, it outputs something like ./FOO/BAR -> ./FOO/BAR, noting that no change has been made). The -T is very important here - it treats the target file as a directory. This will make sure that ./FOO/BAR isn't moved into ./FOO/bar if that directory happens to exist.
Use this together with find to generate a list of commands that will be executed (handy to verify what will be done without actually doing it)
sh
This pretty self-explanatory. It routes all the generated mv commands to the shell interpreter. You can replace it with bash or any shell of your liking.
Using bash, without rename:
find . -exec bash -c 'mv $0 ${0,,}' {} \;