[ is part of Bash syntax

Nooo! Mistake #0 about shell scripting is thinking [ is syntax. It makes it way more weird and inexplicable. [ is a command, just like any other. That's why there needs to be a space between it and the next thing, and why you have to use weird looking flags and such. This is why I prefer the command `test`. It does the same thing as `[`, but is more obviously a command. And when you see it as a command, it's obvious that any command can be used in an if directly; if is just checking the exit code. (Whenever I see someone doing `if [ $? -ne 0 ]`, it makes me cry.)

I'll bite. What should we be using instead of `if [ $? -ne 0 ]`? Because that's pretty standard in my (admittedly very basic) bash.

Instead of

somecommand

if [ $? -ne 0 ]; then echo "it failed"; fi

the parent commenter presumably wants to see

if ! somecommand; then echo "it failed"; fi

Or:

    somecommand || echo "it failed"

if it's just one statement. There are some cases where it just looks more natural. For example:

    start_service || log "already started"

> when you see it as a command, it's obvious that any command can be used in an if directly; if is just checking the exit code

One of the best days of my life

test is [

Indeed, "test" is exactly like "[" except that it doesn't check that its last argument is a "]".

For some reason I've always been amused by "which [". The idea of 'punctuation' being a command or a filename is something that threw me.

...and perhaps surprisingly also a program sitting on disk.

    $ type [
    [ is a shell builtin
    $ [ 1 -gt 0
    bash: [: missing `]'

    $ whereis [
    /bin/[
    $ /bin/[ 1 -gt 0
    # success

You got a root shell out of `/bin/[` ? Impressive :)

Hm, which version of [ is that? I get:

    $ /usr/bin/[ 1 -gt 0 && echo success
    /usr/bin/[: missing `]'
    $ /usr/bin/[ 1 -gt 0 ] && echo success
    success

(This is from coreutils 8.13-3.5 on Debian GNU/Linux)

What ships in OS X 10.9, presumably BSD-derived.