echo -e \e does not print an escape from bash script on macos

Question

I just moved to Mac. I'm using a shared shell script that's running in bash. The script itself works, however it is written to produce colored output, and that is broken.

Here's the first two lines from the script:

#!/bin/bash

echo -e -n "\e[0m\e[32mhks>>>\e[2m "

• My expectation when running it from zsh would be that it produces the output hks>>> in bright green.
• However, the output that is produced is:

  matthiashuttar@mac hks % hks bla
  \e[0m\e[32mhks>>>\e[2m \e[91mfailed to resolve target\e[0m
  

I know it's not a zsh issue, because I can just execute that echo statement as is in zsh and it will produce the output in the correct green color.

Can someone point me towards what I am missing?

Answer 1

MacOS ships an ancient version of bash (3.2.x), so bash scripts that work on other systems might not work on macOS. The version of bash on macOS does not support \e as an escape sequence in echo.

This appears to be a bug in bash 1.x through 3.x, fixed in 4.0. The manual lists \e as one of the escape sequences supported by echo, but help echo lists \E and not \e. (Though digging into the code I can't see where \e and \E are treated differently — but experimentally, they are.)

(There's definitely a bug because of the inconsistency. But I think back then supporting only \E was the desired behavior, presumably because it was a nonstandard extension and there's a habit in shell circles, mostly coming from command line options, that lowercase letters are standard things and uppercase letters are nonstandard things or modern additions. So the bug was that the manual wrongly listed \e.)

printf and $'…' use different code for backslash escapes, and both recognize \e even in bash 3.2.x. Alternatively, you can use an octal escape sequence, which works in all sh-style shells.

So any of the following will work instead of echo -e -n '\e…':

• echo -e -n '\033…' (works in most sh-style shells, but some don't support -e or -n as an option)
• printf '\033…' (note that any % must be doubled; use %s and an extra argument if there's a variable) (works in all sh-style shells)
• printf %b '\033…' (works in all sh-style shells)
• printf '\e…' (note that any % must be doubled; use %s and an extra argument if there's a variable)
• printf %b '\e…'
• echo -n $'\e…'
• echo -n -e '\E…'