zsh error on regex [[:space]]

I'm delighted to see support for zsh. Thank you!

I'm rewriting a bash script into zsh and shfmt complains about that line:

grep --max-count 1 "^$1[[:space:]]" $mainroster

with the error:

`[` must follow a name

I'm not sure what the error means.

Interestingly, I use a similar line in my bash version, where it causes no problem:

grep --max-count 1 "^$1[[:space:]]" "$mainroster"

Thanks, this appears to be a bug, also with a confusing error message.

It's worth noting that what you have here is rather fragile, i.e. zsh only allows it with numeric parameters, but any other parameter breaks.

$ echo "$foo[[:space:]]"
zsh: bad output format specification
$ echo "$1[[:space:]]" 
[[:space:]]

What I mean by that is that something like "^${1}[[:space:]]" is much less error-prone. But I'll try to fix the bug regardless.

Ah, found the part of man zshall which explains this:

One final note, not directly related to subscripting: the numeric names of positional parameters (described below) are parsed specially, so for example $2foo is equivalent to ${2}foo. Therefore, to use subscript syntax to extract a substring from a positional parameter, the expansion must be surrounded by braces; for example, ${2[3,5]} evaluates to the third through fifth characters of the second positional parameter, but $2[3,5] is the entire second parameter concatenated with the filename generation pattern [3,5].

syntax: $1[foo] does not parse as a zsh subscript

I agree that ${1}x is safer than $1x, but when I look for robustness and readability, I don't program in shell! 😏
Thanks for the fix and for shfmt in general. I had been waiting eagerly for zsh support. Now, all I need is zsh support in shellcheck!

fix(deps): update module mvdan.cc/sh/v3 to v3.13.1 (#397)

chore(deps): update module mvdan.cc/sh/v3/cmd/shfmt to v3.13.1 (hetzn…

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zsh error on regex [[:space]] #1288

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zsh error on regex [[:space]] #1288

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mvdan commented on Mar 14, 2026

mvdan commented on Mar 14, 2026

mvdan commented on Mar 14, 2026

charpov commented on Mar 21, 2026

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