rc/sh/monitor

#!/usr/bin/env zsh
# compat: -ash -bash -dash -hush -ksh -mksh -oksh -osh -posh -yash +zsh

monitor() { ### @-
    ### this is [watch(1)](https://www.man7.org/linux/man-pages/man1/watch.1.html)
    ### loosely reimplemented as a shell script.
    ###
    ### ```
    ### usage: monitor [-fs] [-n {period}] {command} [{args...}]
    ### ```
    ###
    ### **NOTE:** there also exists monitor(1) programs provided by
    ### the *389-ds-base* and *dmucs* packages that i don't use.
    local bottom=0 strip=0 interval=2 opt=
    while getopts 'fsn:h' opt; do
        case $opt in
        f) bottom=1;; # align with bottom of terminal
        s) strip=1;; # strip last character assuming it's a newline
        n) interval="$OPTARG";;
        ?) echo -E "usage: $0 [-fs] [-n {period}] {command} [{args...}]"
           [ $opt = h ] && return 0 || return 1;;
        esac
    done
    shift $((OPTIND-1))

    local cmd=${1:?no command specified}
    shift

    function _monclear() {
        [ $bottom -eq 1 ] && printf ${(l:$((LINES*2))::\n:)}
    }
    function _monfit() {
        if [ $strip -eq 1 ]; then
            tail -$((LINES)) | head -c-1
        else
            tail -$((LINES-1))
        fi
    }

    local stop=0
    trap stop=1 INT
    echo -en "\e[H\e[2J"
    while [ $stop -eq 0 ]; do
        echo -en "\e[1J\e[H"
        { _monclear; "$cmd" "$@" 2>&1 } | fold -w $COLUMNS | _monfit
        sleep "$interval" || break
    done
}

[ -n "${preload+-}" ] || monitor "$@"