Detect if MRI Ruby is built with jemalloc library or not, download with `curl -fSL http://bit.ly/ruby-jemalloc-check > ruby-jemalloc-check.sh`

ruby-jemalloc-check.sh

#!/usr/bin/env bash
# vi: ft=sh
#
# © 2019 Konstantin Gredeskoul, Inc., All rights reserved. 
# MIT LICENSE
#
# ————————————————————————————————————————————————————————————————
# This script verifies that the current ruby (in PATH) is linked
# with libjemalloc library for efficient memory utilization.
# It works identically on Linux and Mac OSX.
#
# Ruby versions 2.5 and earlier had a simpler method, typically
# running the following command and expecting the output to
# contain something like '-ljemalloc -lm ... '
#
#     ruby -r rbconfig -e "puts RbConfig::CONFIG['LIBS']"
#
# Unfortunately, this method no longer works with Ruby 2.6
# and later, nor did it ever work with Linux.
#
# For this reason, the following script is provided to verify
# if your Ruby is using jemalloc memory allocator or not.
#
# USAGE:
#   curl -fSL http://bit.ly/ruby-jemalloc-check > ruby-jemalloc-check.sh
#   chmod 755 ruby-jemalloc-check.sh
#   ./ruby-jemalloc-check.sh
#
# ————————————————————————————————————————————————————————————————

set +e

export JM_Quiet=false
export JM_Ruby=false
export JM_Stats=false

export ColorRed="\e[1;31m"
export ColorGreen="\e[1;32m"
export ColorYellow="\e[1;33m"
export ColorBlue="\e[1;34m"
export ColorReset="\e[0m"

# prints the info about current version of ruby
jm::ruby::report() {
  printf "Ruby version being tested:\n  →  ${ColorBlue}$(which ruby) ${ColorYellow}$(jm::ruby::detect)${ColorReset}\n"
}

# returns a string such as "/usr/local/bin/ruby 2.6.4 (x86darwin)"
jm::ruby::detect() {
  local ruby_loc
  if [[ -n $(which rbenv) ]] ; then
    ruby_loc=$(rbenv versions | grep '*' | awk '{print $2}')
    [[ -n ${ruby_loc} ]] && ruby_loc="(rbenv) ${ruby_loc}"
  else
    ruby_loc="$(which ruby) $(ruby -e 'puts "#{RUBY_VERSION} (#{RUBY_PLATFORM})"')"
  fi

  printf "%s" "${ruby_loc}"
}

# prints jemalloc statistics if jemalloc is available
jm::jemalloc::stats() {
  jm::jemalloc::detect-quiet || {
    printf "No Jemalloc was found for the curent ruby $(jm::ruby::detect)\n"
    return 1
   }

  MALLOC_CONF=stats_print:true ruby -e "exit" 2>&1 | less -S
}

jm::jemalloc::detect-quiet() {
  MALLOC_CONF=stats_print:true ruby -e "exit" 2>&1 | grep -q "jemalloc statistics"
  return $?
}

jm::jemalloc::detect-loud() {
  jm::jemalloc::detect-quiet

  local code=$?
  local local_ruby=$(jm::ruby::detect)

  printf "${ColorBlue}Checking if ruby ${local_ruby} is linked with jemalloc... \n\n "
  if [[ ${code} -eq 0 ]]; then
    printf " ✅ ${ColorGreen} — jemalloc was detected.\n"
  else
    printf " 🚫 ${ColorRed} — jemalloc was not detected.\n"
  fi
  printf "${ColorReset}\n"
  return ${code}
}

usage() {
  printf "
USAGE:
  $0 [ -q/--quiet ] [ -r/--ruby ] [ -s/--stats ] [ -h/--help ]

DESCRIPTION:
  Determines whether the currently defined in the PATH ruby
  interpreter is linked with libjemalloc memory allocator.

OPTIONS
  -q/--quiet        Do not print output, exit with 1 if no jemalloc
  -r/--ruby         Print which ruby is currently in the PATH
  -s/--stats        Print the jemalloc stats
  -h/--help         This page.
"
  exit 0
}

# Parse additional flags
while :; do
  case $1 in
    -q|--quiet)
      shift
      export JM_Quiet=true
      ;;
    -r|--ruby)
      shift
      export JM_Ruby=true
      ;;
    -s|--stats)
      shift
      jm::jemalloc::stats
      exit $?
      ;;
    -h|-\?|--help)
      shift
      usage
      exit 0
      ;;
    --) # End of all options; anything after will be passed to the action function
      shift
      break
      ;;
    *)
      break
      ;;
  esac
done

${JM_Ruby}  && { jm::ruby::report; exit 0; }
${JM_Quiet} && { jm::jemalloc::detect-quiet; code=$?; exit ${code}; }

jm::jemalloc::detect-loud