Generate JSON output of docker build step timing, useful for profiling

time-docker-build.sh

#!/bin/bash
#   script: time-docker-build.sh
#
#   All command line arguments are passed to docker build command.
#
#   usage: ./time-docker-build.sh
#

DATE_FORMAT="+%s"

(
    # Output START line
    echo "$(date $DATE_FORMAT) | - 0 - START"

    docker build $* . | \
        grep "^Step" | \
        while read line ;
        do
            # Output build output prefixed with date
            echo "$(date $DATE_FORMAT) | $line";
        done;

    # Output END line
    echo "$(date $DATE_FORMAT) | - -1 - END"
) | (
    # Generate JSON array output.
    #   - START is step: 0
    #   - END is step: -1

    echo "["
    FIRST_RUN=true
    while read line ;
    do
        [[ -z "$FIRST_RUN" ]] && echo ","   # if not first line, print ','

        lineArray=($line)
        time="${lineArray[0]}"          # step is 0th
        step="${lineArray[3]}"          # step is 2nd
        cmd="${lineArray[@]:5}"         # cmd is everything after 5th

        stepNum=${step/\/*/}
        escapedCmd="${cmd//\"/\\\"}"    # escape all double quotes '"'

        echo "  {"
        echo "    \"time\": $time,"
        echo "    \"step\": $stepNum,"
        echo "    \"cmd\": \"$escapedCmd\""
        echo -n "  }"

        unset FIRST_RUN
    done
    echo
    echo "]"
)