ZSH regex capture groups

in

In writing a script for the ZSH shell, I wanted to extract some bits from a string. I looked for a regex solution, using capture groups. I could not figure out how to do it with sed but I found that the [[ ]] format of the test command allows this with the =~ operator. If the test returns true, values are stored in a $match array and can be accessed like $match[1] and so on.

In my use case, I was trying to improve on ZSH’s run-help function. Some of its results say things like:

See the section `ZLE BUILTINS' in zshzle(1).

Why not just show that section of that manpage directly? So I wanted to check if the output was of that format, and if so, extract the section and manpage bits and use them to show the information I would be looking for. After a bit of experimenting I ended up with the regex test looking like:

[[ "$var" =~ "See the section \`([^']+)' in ([^\(]+)" ]]

and the capture groups were accessed like:

man -P "${PAGER:-less} -Ip '${match[1]}'" "$match[2]"

The overall script I created using it ended up something like:

autoload -Uz run-help
function h(){
    if [ -z "$HELPDIR" ]; then
        local HELPDIR="/usr/share/zsh/${ZSH_VERSION}/help"
    fi
    s="$@"
    out=`\run-help "$s" 2> /dev/null`
    if [[ "$out" =~ "See the section \`([^']+)' in ([^\(]+)" ]]; then
        man -P "${PAGER:-less} -Ip '${match[1]}'" "$match[2]"
    else
        \run-help $s
    fi
}

The =~ matching also works similarly in Bash, but there the array is called $BASH_REMATCH instead of $match.

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