Quick tip: how do you rename all files so spaces are converted to underscores?

My friend today asked me how to convert all spaces in filenames under a specified directory to underscores. Also, at the same time lowercase all of the filenames. Here is a quick script to do what is needed. Let us start with creating some test data in a temp directory:

mkdir temp
cd temp
touch Foo FooO "Foo Bar" "FOO BAaR"
\ls | while read -r FILENAME
mv -v "$FILENAME" `echo $FILENAME| tr ' ' '_'| tr '[A-Z]' '[a-z]'`

Note:  I intentionally have slash in front of ls (\ls).  \ls means that we want to make sure there is no ls alias overwriting our command. This is needed if your system has alias setup to display ls in a different way instead of default listing.  mv -v shows us the filenames being renamed as your script goes through the whole dir.  Your output should be like:

`Foo' -> `foo'
`FOO BAaR' -> `foo_baar'
`Foo Bar' -> `foo_bar'
`FooO' -> `fooo'

One of the very powerful commands in this post is the “tr” command. This command is not as popular as sed or awk but it is very useful and simple to use (read more about tr).

If you only needed to convert spaces to underscores and you are using CentOS/Fedora/Redhat, you can use this simpler method. NOTE: this command is not available on all distributions: rename " " "_" *

Learn more about rename command
DISCLAIMER: Please be smart and use code found on internet carefully. Make backups often. And yeah.. last but not least.. I am not responsible for any damage caused by this posting. Use at your own risk.

4 thoughts on “Quick tip: how do you rename all files so spaces are converted to underscores?

  1. LenZ

    Alternatively, you could have used mmv(1):

    mmv “*” “#l1” # Make all file names lowercase
    mmv “* *” “#1_#2” # Replace blank with underscore

    You may have to repeat the second step for files with multiple blanks.

  2. Bob Jewell

    If you had Foo and FOO in the same directory, you’d end up overwriting one of them, I believe.
    You could use –backup=numbered or something like that with your move command to automatically add numbers to the files and then do a find for all numbered files and solve the errors manually in a clean way.

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