shellscript (zsh): Infinite wait for the success-status of given `command` for polling something

waitfor

#!/usr/bin/zsh

help='Usage: waitfor interval command [args ...]

Infinite wait for the success-status (0) of given `command` for polling something.

arguments
    interval:   0.0 .. 99 [sec]
    command:    command for polling something
    args:       if you need'

[ "$1" = '--help' ] && echo $help && exit 0
[ $# -lt 2 ] && echo $help && exit 1

re='^[0-9]+([.]+[0-9]+)?$'
[[ ! $1 =~ $re ]] && echo "Error: invalid interval[sec]: $1" && exit 1

sec=$1

shift
cmd=$1
! which $cmd > /dev/null && echo "Error: Command not found: $cmd" && exit 1

shift
args=$*

while true; do
    echo -n .
    $cmd $args > /dev/null 2>&1 && exit 0
    sleep $sec
done

exit 1

ZZ_example.txt

$ cd ~/Downloads
$ ls foo            # `foo` does *not* exist
ls: cannot access 'foo': No such file or directory

$ waitfor 1 ls foo
....

#### begin: another shell 
$ touch ~/Downloads/foo
#### end: another shell 

........%

$ echo $?
0                # returns 0 (success code)

#
# perhaps, need timeout? use `timeout` command like below:
#

$ timeout 10 waitfor 1 ls foo             # timeout = 10 sec

this script should not be used because it fails when using with pipe.
e.g.: waitfor 1 mount | grep sdb

all i want does already exist, until built-in word.

until mount | grep -q sdb; do sleep 0.1; done

no help on zsh. but as far as i can tell from looking at man zshmisc, it seems to be a cousin of while...sucks!