Extract URLs from an input CSS document

csslinks.sh

#! /usr/bin/env bash
#>------------------------------------------------------------------------------
#>
#> [ csslinks ]
#>
#>    Extract URLs from an input CSS document
#>
#> USAGE:
#>
#>    ./csslinks <INPUT>
#>    ./csslinks <OPTION>
#>
#>    where "INPUT" is some CSS data or CSS file reference; and where "OPTION"
#>    is one of the following:
#>
#>                |
#>    -h, --help  | Print this help text to the terminal
#>                |
#>
#> ATTRIBUTION:
#>
#>    Created on 20201105 by h8rt3rmin8r (161803398@email.tg)
#>    Source (pastebin.com): https://bit.ly/2HZYUoa
#>    Source (github.com): https://bit.ly/2TWIxec
#>
#>------------------------------------------------------------------------------

function _help() {
    cat "${0}" \
        | grep -E '^#[>]' \
        | sed 's/^..//'
    
    return $?
}

function _main() {
    dos2unix \
        | tr -s '\t' ' ' \
        | tr -s '\n' ' ' \
        | tr -d ' ' \
        | sed 's/url[(]./ /g' \
        | tr ' ' '\n' \
        | tail -n +2 \
        | sed 's/.[)].*//' \
        | grep --color=never -E '.'
    
    return $?
}

if [[ "${1}" =~ ^[-][hH]$ || "${1}" =~ ^[-]+help$ ]]; then
    _help
    exit $?
fi

if [ -t 0 ]; then
    if [[ "x${1}" == "x" ]]; then
        exit 1
    elif [[ -f "${1}" ]]; then
        _main <"${1}"
    else
        _main <<<"$@"
    fi
else
    _main
fi

exit $?