Re: code not working ..

[Greg Wooledge]

On Wed, Sep 11, 2024 at 01:35:15 +0200, alex xmb sw ratchev wrote:
> hmm hard to code an args check like this ..

Are you trying to determine whether a STRING argument appears in a LIST?

I have a feeling that's what you're trying to do.

Many people think there should be some "clever" way to do this using
list-to-string serialization and delimiters.

The actual BEST way to do it is to iterate over the list, do a simple
comparison of your string against each list element, and stop if you
have a match.

Loops are not evil.  Loops are your friend.  You don't need to do
backflips trying to avoid writing them.


# Usage: isin stringvarname arrayvarname
# Returns 0 (true) if the string pointed to by stringvarname appears
# as an element of the array pointed to by arrayvarname.  Otherwise,
# returns 1.

isin() {
    local -n _isin_needle="$1"      # Using namerefs means we must
    local -n _isin_haystack="$2"    # use ridiculous local variable names
    local _isin_x                   # to try to avoid collisions.

    for _isin_x in "${_isin_haystack[@]}"; do
        [[ $_isin_needle = "$_isin_x" ]] && return 0
    done
    return 1
}


hobbit:~$ var=foo
hobbit:~$ arr=(a 12 foo bar)
hobbit:~$ isin var arr ; echo "$?"
0
hobbit:~$ var=fo
hobbit:~$ isin var arr ; echo "$?"
1


Of course, this function could be written in many other ways.  You might
choose to pass the first argument as a value, rather than a variable
name that must be dereferenced.  You might expand the array in the caller,
and pass each array element as an additional argument.  These are all
reasonable choices.

What's *not* as reasonable is trying to join the array into a string with
a weird delimiter like $'\xff' before, between and after every element,
and then match that string against a pattern like *$'\ff'"$string"$'\ff'*.
I wish people would stop doing that.  I know they won't, but I can dream.