example utils.sh

utils.sh

#!/bin/bash

# Common utility functions for bash scripts,
# - fatal -- use like `some_cmd || fatal "Some cmd failed"`
# - debug -- use like `debug "This is a debug message"`
# - timer -- use like `tm some_cmd` as a wrapper
# - retry -- use like `retry some_cmd` as a wrapper, retries with exp. backoff
#
# Source this bash like so: `. util.sh`
#
# *** Requires `jq` to be installed.
#
# Debug and timer is only printed when DEBUG=1
# Output is printed as JSON when JSON_OUTPUT=1
#

# echo message to stderr and exit process with non-zero return code
fatal() {
    # exit process with an error message
    # use json syntax when JSON_OUTPUT is defined
    rc=$?
    if [ -z "$JSON_OUTPUT" ]; then
      echo "E $(date -u +%s%3N) ${BASH_SOURCE[1]}:${BASH_LINENO[1]}:${FUNCNAME[1]}:error:$rc: $*" >&2
    else
      echo "{\"type\":\"fatal\",\"time\":\"$(date -u +%s%3N)\",\"source\":\"${BASH_SOURCE[1]}\",\"line\":\"${BASH_LINENO[1]}\",\"func\":\"${FUNCNAME[1]}\",\"code\":\"$rc\",\"message\":\"$*\"}" \
        | jq -Sc . >&2
    fi
    exit $rc
}

# echo message to stderr when DEBUG=1
debug() {
    # print a debug message to stderr when DEBUG is defined;
    # use json syntax when JSON_OUTPUT is defined
    [ -z "$DEBUG" ] && return
    if [ -z "$JSON_OUTPUT" ]; then
      echo "D $(date -u +%s%3N) ${BASH_SOURCE[1]}:${BASH_LINENO[1]}:${FUNCNAME[1]}:debug: $*" >&2
    else
      echo "{\"type\":\"debug\",\"time\":\"$(date -u +%s%3N)\",\"source\":\"${BASE_SOURCE[1]}\",\"line\":\"${BASH_LINENO[1]}\",\"func\":\"${FUNCNAME[1]}\",\"message\":\"$*\"}" \
        | jq -Sc . >&2
    fi
}

# measure time duration of executed process and echo when DEBUG=1
tm() {
    # execute a command and print its timing to stderr
    # use json syntax when JSON_OUTPUT is defined
    # in json format, capture the command stdout and stderr into json
    [ -z "$DEBUG" ] && { "$@"; return $?; }
    START=$(date +%s%3N)
    if [ -z "$JSON_OUTPUT" ]; then
      "$@"; rc=$?
      END=$(date +%s%3N)
      echo "T $(date -u +%s%3N) ${BASH_SOURCE[1]}:${BASH_LINENO[1]}:${FUNCNAME[1]}:$(( END - START ))ms: $*" >&2
    else
      stdout_pipe=$(mktemp -u)
      stderr_pipe=$(mktemp -u)
      trap 'cat $stdout_pipe >/dev/null 2>&1; cat $stderr_pipe >/dev/null 2>&1; rm -f $stdout_pipe $stderr_pipe' RETURN
      "$@" 1>"$stdout_pipe" 2>"$stderr_pipe"; rc=$?
      END=$(date +%s%3N)
      echo "{\"type\":\"time\",\"time\":\"$(date -u +%s%3N)\",\"source\":\"${BASE_SOURCE[1]}\",\"line\":\"${BASH_LINENO[1]}\",\"func\":\"${FUNCNAME[1]}\",\"ms\":\"$(( END - START ))\",\"cmd\":\"$*\"}" \
        | jq -Sc --arg stdout "$(cat "$stdout_pipe")" --arg stderr "$(cat "$stderr_pipe")" '. * { "stdout": $stdout, "stderr": $stderr }' >&2
    fi
    return $rc
}

retry() {
    max_retries=${MAX:-5}
    retries=0
    until tm "$@" && [ "$retries" -lt "$max_retries" ]; do
        duration=$(( 2 ** retries ))
        retries=$(( retries + 1 ))
        debug "Retrying after ${duration}s"
        sleep "$duration"
    done
    fatal "Maximum retries ($MAX) reached. Could not perform $*"
}

# check that script is being executed by root, or abort
check_root() {
  [ "$(id -u)" != '0' ] && \
      fatal "Must run $0 as root or using sudo."
}

# check that the docker command exists, or abort
check_docker() {
    command -v docker >/dev/null \
        || fatal "==> Could not find Docker installed."
}

mkdir_chown() {
    debug "Creating directories & changing to root ownership: $*"
    mkdir -p "$@"
    chown -R 0:0 "$@"
}

# join multiple strings into a long string separated by first arg. value
strings_join() {
    local IFS="$1"
    shift
    echo "$*"
}

eval_os_release() {
    # set environment variables OS_ID and OS_VERSION_ID from Linux release info
    ## possible OS_ID values:
    # ubuntu debian rhel centos fedora amazon
    eval "$(sed -ne '/^\(VERSION_ID\|ID\)=/s!^!export OS_!gp' /etc/os-release)"
}