Keep retrying yarn script until it passes

Question

I am new to bash and wondering if there is a way to run a script x amount of times until it succeeds? I have the following script, but it naturally bails out and doesn't retry until it succeeds.

yarn graphql
if [ $? -eq 0 ]
then
  echo "SUCCESS"
else
  echo "FAIL"
fi

I can see there is a way to continuously loop, however is there a way to throttle this to say, loop every second, for 30 seconds?

while :
do
    command
done

Answer 1

I guess you could devise a dedicated bash function for this, relying on the sleep command.

E.g., this code is freely inspired from that code by Travis, distributed under the MIT license:

#!/usr/bin/env bash
ANSI_GREEN="\033[32;1m"
ANSI_RED="\033[31;1m"
ANSI_RESET="\033[0m"

usage() {
    cat >&2 <<EOF
Usage: retry_until WAIT MAX_TIMES COMMAND...

Examples:
  retry_until 1s 3 echo ok
  retry_until 1s 3 false
  retry_until 1s 0 false
  retry_until 30s 0 false
EOF
}

retry_until() {
    [ $# -lt 3 ] && { usage; return 2; }
    local wait_for="$1"  # e.g., "30s"
    local max_times="$2"  # e.g., "3" (or "0" to have no limit)
    shift 2
    local result=0
    local count=1
    local str_of=''
    [ "$max_times" -gt 0 ] && str_of=" of $max_times"
    while [ "$count" -le "$max_times" ] || [ "$max_times" -le 0 ]; do
        [ "$result" -ne 0 ] && {
            echo -e "\n${ANSI_RED}The command '$*' failed. Retrying, #$count$str_of.${ANSI_RESET}\n" >&2
        }
        "$@" && {
            echo -e "\n${ANSI_GREEN}The command '$*' succeeded on attempt #$count.${ANSI_RESET}\n" >&2
            result=0
            break
        } || result=$?
        count=$((count + 1))
        sleep "$wait_for"
    done
    [ "$max_times" -gt 0 ] && [ "$count" -gt "$max_times" ] && {
        echo -e "\n${ANSI_RED}The command '$*' failed $max_times times.${ANSI_RESET}\n" >&2
    }
    return "$result"
}

Then to fully answer your question, you could run:

retry_until 1s 30 command