Wait for file to become readable

wait-for-file.sh

#!/usr/bin/env bash
# https://gist.github.com/siberex/d1c07389333d9cdb1c9e6853ec70c98b

# Wait for file to become readable
# Similar to https://github.com/vishnubob/wait-for-it

# Usage:
# wait-for-file.sh -t 10 -p /tmp/something -- echo "ok"

WAITFORIT_cmdname=${0##*/}
echoerr() { echo "$@" 1>&2; }

usage() {
    cat <<USAGE >&2
Usage:
    $WAITFORIT_cmdname -p /path/to/file [-t timeout] [-- command args]
    -p PATH | --path=PATH           Path to test for readability
    -t TIMEOUT | --timeout=TIMEOUT  Timeout in seconds, default is 15
    -- COMMAND ARGS                 Execute command with args after the test finishes
USAGE
    exit 1
}

# Exit script when command fails
set -o errexit
# Return value of a pipeline is the value of the last (rightmost) command to exit with a non-zero status
set -o pipefail

# process arguments
while [[ $# -gt 0 ]]; do
    case "$1" in
    -t)
        WAITFORIT_TIMEOUT="$2"
        if [[ $WAITFORIT_TIMEOUT == "" ]]; then break; fi
        shift 2
        ;;
    --timeout=*)
        WAITFORIT_TIMEOUT="${1#*=}"
        shift 1
        ;;
    -p)
        WAITFORIT_PATH="$2"
        if [[ $WAITFORIT_PATH == "" ]]; then break; fi
        shift 2
        ;;
    --path=*)
        WAITFORIT_PATH="${1#*=}"
        shift 1
        ;;
    --)
        shift
        WAITFORIT_CLI=("$@")
        break
        ;;
    --help)
        usage
        ;;
    *)
        echoerr "Unknown argument: $1"
        usage
        ;;
    esac
done

if [[ "$WAITFORIT_PATH" == "" ]]; then
    echo "Error: you need to provide a path to test."
    usage
fi

# Default is 15 seconds
WAITFORIT_TIMEOUT=${WAITFORIT_TIMEOUT:-15}

WAITFORIT_start_ts=$(date +%s)

if [[ $WAITFORIT_TIMEOUT -gt 0 ]]; then
    echo "$WAITFORIT_cmdname: waiting $WAITFORIT_TIMEOUT seconds for readability: $WAITFORIT_PATH"
else
    if [ -r "$WAITFORIT_PATH" ]; then
        WAITFORIT_TIMEOUT=-1
    else
        WAITFORIT_TIMEOUT=0
    fi
fi

while [[ $WAITFORIT_TIMEOUT -gt 0 ]]; do
    if [ -r "$WAITFORIT_PATH" ]; then
        WAITFORIT_TIMEOUT=-1
        break
    fi

    sleep 1
    WAITFORIT_TIMEOUT=$((WAITFORIT_TIMEOUT - 1))
done

if [[ $WAITFORIT_TIMEOUT -eq -1 ]]; then
    WAITFORIT_end_ts=$(date +%s)
    echo "$WAITFORIT_cmdname: $WAITFORIT_PATH is available after $((WAITFORIT_end_ts - WAITFORIT_start_ts)) seconds"

    # shellcheck disable=SC2128
    if [[ $WAITFORIT_CLI != "" ]]; then
        exec "${WAITFORIT_CLI[@]}"
    else
        exit 0
    fi
else
    echoerr "Timeout"
    exit 1
fi