In my book Linux Phrasebook I told readers that if they want to use the output of a command inside another command (known as command substitution), they should use $() instead of ` (the backtick). In other words, instead of this:

mkdir folder_`date +%Y%m%d`

Do this:

mkdir folder_$(date +%Y%m%d)

Here’s a slightly more complicated (yet overly simplified, as you’ll see) example. Instead of this:

for i in `cat /path/to/some/file`
  something $i

You should instead do this:

for i in $(cat /path/to/some/file)
  something $i

A few days ago, a reader wrote to me & asked the following:

I’m seeking clarification on a position you took in your book, advising readers to use $() over backticks. Could you please explain why?

Here’s what I wrote back:

Here are some reasons:

  • $() is easier to read, especially with smaller fonts that can make the backtick really hard to see. To me, this is a big one.
  • The backtick is very similar to a apostrophe; heck, a lot of the time I’ve seen backticks used as apostrophes!
  • The $() makes nesting command substitutions easier. In other words, you can do this: cd $(mkdir folder_$(date +%Y%m%d)).
  • It’s more like the programming notations that others are familiar with. I don’t know of anything that uses the backtick.
  • It’s recommended that you do it that way!

More info: