[Feature request] add support for zsh shell

[superbonaci]

shellcheck version 0.9.0
Add support for shellcheck --shell=zsh since is highly used. Comes by default in Kali linux and macOS (zsh 5.8.1).

Example code:

#!/bin/bash
SOMETEXT=""
NUMBER="0"
if [ "$SOMETEXT" == "" ] && [ "$NUMBER" -eq 0 ]; then echo "match"; else echo "no match"; fi

zsh will complain while bashwill work normally

$ bash check.sh
match

$ zsh check.sh
../check.sh.sh:4: = not found

The fix for both is this:

#!/bin/bash
SOMETEXT=""
NUMBER="0"
if [ "$SOMETEXT" = "" ] && [ "$NUMBER" -eq 0 ]; then echo "match"; else echo "no match"; fi

[superbonaci]

zshalso fails here:

#!/bin/bash
SOMETEXT=""
NUMBER="0"
if [ "$SOMETEXT" = "" ] && [ "$NUMBER" -eq 0 ]; then echo "match"; else echo "no match"; fi

MONEY="2"
if [ "$MONEY" -eq $(("$NUMBER" + 2)) ]; then echo "match"; else echo "no match"; fi

$ zsh check.sh
match
check.sh:7: bad math expression: illegal character: "

$ bash check.sh
match
match

[FranklinYu]

1. Double bracket ([[ ]]) in Zsh allows double dash. IMO, if ShellCheck is to support Zsh, it should simply recommend double bracket.
2. If the executable is supposed to run under multi-shell, then it is probably a shell library that people source in their shell (e.g. nvm), instead of some executable script that people execute under a sub-shell (e.g. ./configure). In this case I recommend no shebang (since the shebang is misleading anyway).
3. Best practice in Bash doesn’t mean best practice in Zsh. Amount of work might not be trivial to add rules for Zsh.

[wakco]

Apple deprecated their inclusion of bash in 2019, as newer versions of bash than those used by Apple are GPLv3, while zsh is not. As such zsh has been the default on macOS since macOS 10.15 Catalina (released 2019), which https://support.apple.com/HT208050 confirms.

Sooner or later Apple will remove bash from macOS, so having a tool like ShellCheck be ready for when that happens, would be greatly appreciated.

(typo fixed, thanks @TinCanTech)

[TinCanTech]

having a tool like spellcheck be ready

That needs a shellcheck [SCnnnn] number.

[superbonaci]

Some information (2019 posts):

• Moving to zsh
• MOVING FROM BASH TO ZSH: TERMINAL CHANGES IN MACOS CATALINA

[brother]

This is a dupe of #809 .