Allowing comments in interactive zsh commands

Question

It might be useful to allow comments in zsh commands written on the command line, as in bash, but

% echo test # test
zsh: bad pattern: #

Any way to get the same behaviour as in the bash shell?

Answer 1

$ setopt interactive_comments
$ echo hello # comment
hello

By default, the zsh shell enables the interactive_comments shell option in scripts (non-interactive shells in general), but not when running an interactive session.

The relevant bit from the zsh manual:

COMMENTS
In non-interactive shells, or in interactive shells with the INTERACTIVE_COMMENTS option set, a word beginning with the third character of the histchars parameter (# by default) causes that word and all the following characters up to a newline to be ignored.

Without this shell option set, you'd only get the bad pattern error if the extended_glob shell option is set. With extended_glob set, x# would match zero or more of the pattern x and x## would match one or more of the pattern x (these correspond to the regular expression modifiers * and +). This means that with extended_glob set and interactive_comments unset, the shell is complaining about the syntax used in an extended filename globbing pattern modifier you used unknowingly.

---

The values in histchars are by default !^#, and the first two characters are used in history expansions.

Since comments in zsh are delimited by $histchars[3], changing this character will change what text is considered to be a comment:

$ setopt extended_glob
$ echo hello # hello : hello
zsh: bad pattern: #

$ unsetopt extended_glob
$ echo hello # hello : hello
hello # hello : hello

$ setopt interactive_comments
$ echo hello # hello : hello
hello

$ histchars[3]=:
$ echo hello # hello : hello
hello # hello

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Interestingly (?), the bash shell also has an interactive_comments shell option, but this is turned on by default in interactive shells:

$ echo hello # hello
hello

$ shopt -u interactive_comments
$ echo hello # hello
hello # hello