Command Substitution in Bash

by Audrey M. Roy Greenfeld | Wed, Jan 1, 2025

## Simple Command Substitution

Use $() not backticks

%%bash
echo "Current directory is $(pwd)"

It also works with backticks, but it's not the best way:

%%bash
echo "Current directory is `pwd`"

(Because when you nest these, you have to escape the backticks)

Example: Moving Untracked Files to _drafts Folder

%%bash
git ls-files --others --exclude-standard

%%bash
mv $(git ls-files --others --exclude-standard) ./_drafts

It works for me and I'd be happy stopping here, but in the real world where files have spaces, it'll break.

Fancy Command Substitution With xargs

xargs lets you map a list to any command. Here I would use it like:

%%bash
git ls-files --others --exclude-standard | xargs -I {} mv {} ./_drafts/

The untracked files list is piped to xargs, which lets us run a command for each line in the list. Then mv is run for each file in the list.

-I {} is needed to put the filename somewhere other than the end of the mv command. Here, -I enables string replacement, and {} is the placeholder string that gets replaced.