Bash shell if operator

Question

I write a function like this to .commands file, and I imported .commands in .zshrc

function testA() {
  echo "start"
  if [ "$1" == "a" ]; then
    echo "ok"
  fi
  echo "end"
}

And when I run testA a in terminal

start
testA:2: = not found

What is the problem here?

Are you sure this is the complete code? I am getting `start ok end` just fine. How are you sourcing the function code into your Bash session? — iBug, Jun 30 '22 at 09:32
This doesn't look like Bash. Bash does not have a builtin `which` that can display shell functions. Only Zsh has a builtin `which` command that matches your output. (Also I've never seen anyone decorating Bash like that). — iBug, Jun 30 '22 at 09:37
So why are you putting Bash in your question title, and tagging [tag:bash]? In case you weren't aware, Bash and Zsh are two vastly different (though partially compatible) shell implementations. — iBug, Jun 30 '22 at 09:39
https://stackoverflow.com/questions/669452/are-double-square-brackets-preferable-over-single-square-brackets-in-b — 0stone0, Jun 30 '22 at 09:41
@iBug sorry for my lack of knowledge. I though they were the same. — Danny, Jun 30 '22 at 09:45
A single "=" in the test is enough, why use two? Try "help test" in bash. — linuxfan says Reinstate Monica, Jun 30 '22 at 09:49

score 1 · Accepted Answer · answered Jun 30 '22 at 09:50

Chapter 12 – "Conditional Expressions" of the zsh documentation states:

A conditional expression is used with the [[ compound command to test attributes of files and to compare strings.

This means, changing your conditional expression to use [[ ... ]] instead of [ ... ] should make it work:

function testA() {
  echo "start"
  if [[ "$1" == "a" ]]; then
    echo "ok"
  fi
  echo "end"
}

score 0 · Answer 2 · answered Jun 30 '22 at 12:19

You can simplify the problem to simply type a [a == a] or echo ==. This will also produce this error. The reason is that a = has specific meaning to zsh, unless it is followed by a white space.

You have three possible workarounds:

Either quote that parameter, i.e.

[ $1 "==" a ]

or use a single equal sign, i.e.

[ $1 = a ]

or use [[, which introduces a slightly different parsing context:

[[ $1 == a ]]

score -1 · Answer 3 · answered Jun 30 '22 at 09:40

-1

    $ cat fun.sh
  function test() {
  echo "start"
  if [ "a" == "a" ]; then
    echo "ok"
  fi
  echo "end"
}

Source script file

 $ source fun.sh

Output:

$ test
start
ok
end

answered Jun 30 '22 at 09:40

Karthee Kumar Vanama

29
3

Bash shell if operator

3 Answers3