I would rewrite this as a shell function:

spaces2underscores() {
   for i in "$@"; do
      mv -iv "$i" "${i// /_}";
   done
}

Usage:

spaces2underscores *
spaces2underscores */*.txt

It’s also easy to make the default *:

if test $# -eq 0; then
   set -- *  # set "$@" to all files in the current directory
fi

The bash manual even says that functions can do everything aliases can do, and are preferred.

Aliases are a bit hacky from an implementation point of view and don’t compose as nicely. Shell aliases and functions are somewhat analogous to C macros and C functions – aliases are a lexical construct, not really part of the language proper. There’s a somewhat confusing rule about trailing spaces in aliases.

That said, I am resigned to implementing aliases in Oil, because even I have aliases in my .bashrc from 10 years ago ! :-/

Note that in dired you can do C-c C-q to make the buffer editable, rename or modify the files however you want, then commit the changes via C-c C-c

For those, like me who were wondering what dired even is:

“Dired makes an Emacs buffer containing a listing of a directory, and optionally some of its subdirectories as well. You can use the normal Emacs commands to move around in this buffer, and special Dired commands to operate on the listed files.”

https://www.gnu.org/software/emacs/manual/html_node/emacs/Dired.html

Love dired & wdired! Emacs magic at its best.

If I’m on the command line I often go for the humble Perl-based rename utility

http://manpages.ubuntu.com/manpages/xenial/man1/prename.1.html

I think the equivalent command is

rename 's/ /_/g' *

(Can’t remember if you need the g modifier or not, I’m not near my laptop to check…)

I had no idea dired had an editable mode! That’s a game-changer for me.

Well, in case you are in Emacs, finding a faster way is as simple as…

(defun spaces-to-underscores()
  (interactive)
  (replace-string " " "_"))

And then bind it to a key that you like. The perks of the modular editor!

I’m using this: https://paste.xinu.at/HQx/ I call it remove_special

If you’re already an Emacs user you probably know this, but note that you can use dired and eshell via tramp, meaning you can do all those things without leaving you local Emacs instance.

Speaking of bash aliases, they can be great fun.

https://twitter.com/awnumar/status/914522652164935685

What is the magic behind ${i// /_}"

The last file manager I used that wasn’t a command line was Directory Opus Magellan II on the Amiga, twentyish years ago. Nothing has compared yet, and I’m too comfortable and too fast now with the shell to go back.

Alternatively, in zsh:

zmv -n '*' '${f// /_}'

(This will also ensure the replacement’s don’t overlap.)

One snafu with aliases that I never found a great work-around was using date or cal or anything that is mutable, would be sort of galvanized after that bash/zsh profile was set. One would have to source that profile file to get the current, in my case, time. So, it didn’t work for things like that (which was quite a few aliases). A quick hack to make this work is welcomed, BTW.