Expanded solution to https://codegolf.stackexchange.com/a/182455/86147

ppcg-connect4.zsh

zip_and_transpose() {
# for convenience, we zip our leading spaces (which provide the offset for diagonal cases) here
# Using ^^ will wrap to previous entries until "argv" is exhausted (this is only useful in the first call)
    for s line (${spaces:^^argv})
        s+=$line &&   # concatenate the spaces onto the start of the line
        for (( i=0 ; i++ < $#s; ))
            a[i]+=$s[i]
}
spaces=(+) # we need to declare this an an array from the start for the zip to work correctly


# zip_and_transpose will append to elements of a.
# We must ensure:
#   1: a is an array (so a[i]+=... will append to an element, not insert into a string)
#   2: the existing contents are separated from the new conents
# ${foo/%/bar} will append 'bar' onto each element of foo
# a=(...) will set a as an array
# We initialize a with the contents of the command line parameters

# === HORIZONTAL (implicit) ===
a=(${@/%/_})
# === VERTICAL ===
zip_and_transpose $@

# === DIAGONAL 1 ===
a=(${a/%/-})
# This is the simplest way I found to create increasing spaces ('_' '__' '___' ...)
# The (l:expr:) flag padds the parameter to width 'expr' with spaces. I add the '_'
# at the end to ensure that the length starts at 1.
for s;spaces[++j]=${(l:j:)}_

# === DIAGONAL 2 ===
a=(${a/%/ })
zip_and_transpose ${(Oa)@}      # rows in inverse order

# a basic test ternary to finish.
[[ $a = *XXXX* ]]&&<<<X||<<<Y

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