Artboard 16light, inspiration, solution, idea, innovation,ionicons-v5_logosGoogle Sheets iconSwift icon
Published at
Updated at
Reading time
1min
This post is part of my Today I learned series in which I share all my web development learnings.

I came across a tweet by Guillermo Rauch. He shared this little snippet.

$ which [
/bin/[

What's that? I rarely do bash scripting so I'm always happy to learn more about it.

Guillermo was also so kind to also share a doc explaining this. If you prefer the TL;DR... here we go:

In bash there is a test command. You can use it to e.g. check if a file exists (with the -e flag) or if a file path points to a directory (with the -d flag). There are also many more options available and you can have a look executing man test. In bash scripts you probably use test inside of an if condition. So how does an if condition looks like in bash?

if test -e /etc/passwd; then
  echo "Alright man..." >&2
else
  echo "Yuck! Where is it??" >&2
  exit 1
fi

I found the example above online and well... this puzzled me. I always assumed that if conditions have to include [] in bash. And that's my learning today!

It turns out that [] are not bash syntax but an actual bash command.

$ which [

[: shell built-in command

$ man [
TEST(1)                   BSD General Commands Manual                  TEST(1)
NAME
     test, [ -- condition evaluation utility

SYNOPSIS
     test expression
     [ expression ]
...  
...

There are even manual pages for it but you see that the displayed man pages are the man pages of test. So this means that [ and test are actual the same thing. ๐Ÿ˜ฒ

$ test -e /does/not/exist
FAIL: 1

$ [ -e /does/not/exist ]
FAIL: 1
Was this TIL post helpful?
Yes? Cool! You might want to check out Web Weekly for more quick learnings. The last edition went out 14 days ago.

Related Topics

Related Articles