Bash snippets

#Bash.md

Bash scripts and snippets

bash-recipes.sh

#
# Common recipes and tricks
#

# Check for missing commands & tools
which foo > /dev/null || { echo -e "💥 Error! Command foo not installed"; exit 1; }

# Single variable
[[ -z "$SOMEVAR" ]] && { echo "💥 Error! Required variable SOMEVAR is not set!"; exit 1; }

# List of many variables (make sure `set -u` is NOT used)
for varName in REQUIRED_VAR ALSO_REQUIRED SO_IS_THIS; do
  varVal=$(eval echo "\${$varName}")
  [[ -z $varVal ]] && { echo "💥 Error! Required variable '$varName' is not set!"; varUnset=true; }
done
[[ $varUnset ]] && exit 1

cert-generate.sh

#!/bin/bash

NAME="cert"
DOMAIN="localhost"
#DOMAIN="myapp.benco.io"
IP="12.34.56.78"
DAYS="3650"

# Create a self-signed cert with a single command, with SNI/SAN
openssl req -x509 -newkey rsa:4096 -sha256 -days "$DAYS" -nodes \
  -keyout "$NAME".key -out "$NAME".pem -subj "/CN=$DOMAIN" \
  -addext "subjectAltName=DNS:$DOMAIN,IP:$IP"

# Convert to a PKCS12 file, you might want it in that format I dunno ¯\_(ツ)_/¯
#openssl pkcs12 -export -out "$NAME".p12 -inkey "$NAME".key -in "$NAME".pem

mkcert.md

Using mkcert with WSL

Using mkcert with WSL can be a little tricky as it creates a root CA for you and installs it in the relevant place for the OS to be trusted. If you run this in WSL it will result in your browser over on the Windows side still not trusting the certs you create with mkcert.

This is a workaround / solution:

• Install root CA: mkcert -install
• Convert the root CA to PKCS12, run: openssl pkcs12 -export -out rootCA.pfx -inkey $(mkcert -CAROOT)/rootCA-key.pem -in $(mkcert -CAROOT)/rootCA.pem
  • Specify no password, just hit enter
• Run explorer.exe .
• In Windows Explorer; double click the rootCA.pfx file to import the certificate
  • Pick the "Place all certificates in the following store" option
  • Select "Trusted Root Certification Authorities"
• Run: mkcert localhost or any other name (e.g. mkcert foo.example.net) to generate a certificate and use certs with whatever server/software/SDK as normal
• Delete the rootCA.pfx file

port-check.sh

#!/bin/bash

host=localhost
port=8080
maxTries=3
sleep=5

tries=0
while ! nc -z $host $port; do  
  echo "Waiting ${sleep}s for $host:$port to accept connections"
  sleep $sleep
  tries=$((tries+1))
  if [ $tries -ge $maxTries ]; then
    echo "FAILED: Unable to connect to the $host:$port after $maxTries tries"
    exit 1
  fi
done
echo "Port $port is available, $host is online"

quick-csr.sh

#!/bin/bash

# Quickly create a new CSR with a new key

DOMAIN=${1:-"blah.example.net"}
FILE_BASENAME=${2:-"example_net"}
LOCATION="London"
COUNTRY="GB"
ORG="Damage Inc."

openssl req -new -newkey rsa:2048 -nodes \
-out "${FILE_BASENAME}.csr" \
-keyout "${FILE_BASENAME}.key" \
-subj "/C=${COUNTRY}/ST=/L=${LOCATION}/O=${ORG}/CN=${DOMAIN}"

template.sh

#!/usr/bin/env bash
set -euo pipefail

if [[ "${TRACE-0}" == "1" ]]; then set -o xtrace; fi

if [[ "${1-}" =~ ^-*h(elp)?$ ]]; then
  echo -e "Usage: $(basename "$0") some-args\nBlah blah change this text"
  exit
fi

cd "$(dirname "$0")"

# Rest of the script

url-check-simple.sh

#!/bin/bash
declare count=0 maxTime=30
[[ $# < 2 ]] && { echo "💬 Pass URL and content check as args"; exit 1; }
while (( $count < $maxTime )); do
  # Remove the grep if you don't need content checking
  curl -sSL $1 | grep $2
  if [ $? -eq 0 ]; then
    echo "😁 URL check passed, content match found!"
    exit 0
  else
    echo "⌚ URL check failed, trying again in 1 second"
    sleep 1
    ((count=count+1))
  fi
done
echo "💥 Giving up after $maxTime seconds, check failed!"
exit 1

url-check.sh

#!/bin/bash

declare -i time=60
declare -i delay=5
declare -i count=5
declare -i okCount=0
declare -i elapsed=0
declare isUp="false"

# Display usage
usage(){
echo -e "\e[32m╭──────────────────────────────────────────────────────────────╮"
echo -e "│   🌍 \e[94murl-check.sh \e[96mCheck URL endpoint for HTTP responses 🚀\e[32m   │"
echo -e "╰──────────────────────────────────────────────────────────────╯"
echo -e "\n\e[95mParameters:\e[37m"
echo -e "     -u, --url       \e[33mURL to check (required)\e[37m"
echo -e "     [-t, --time]    \e[33mMaximum number of seconds to poll for \e[92m(default: 60)\e[37m"
echo -e "     [-d, --delay]   \e[33mDelay in seconds between requests \e[92m(default: 5)\e[37m"
echo -e "     [-c, --count]   \e[33mHow many successes to receive before exiting \e[92m(default: 5)\e[37m"
echo -e "     [-s, --search]  \e[33mOptional content check, grep for this string in HTTP body \e[92m(default: none)\e[37m"
echo -e "     [-h, --help]    \e[33mShow this help text\e[37m"
}

if ! OPTS=$(getopt -o u:t:d:c:s:h --long url:,time:,delay:,count:,search:,help -n 'parse-options' -- "$@"); then echo "Failed parsing options." >&2 ; usage; exit 1 ; fi
eval set -- "$OPTS"

while true; do
  case "$1" in
    -u | --url ) url="$2"; shift; shift;;
    -t | --time ) time="$2"; shift; shift;;
    -d | --delay ) delay="$2"; shift; shift;;
    -c | --count ) count="$2"; shift; shift;;
    -s | --search ) search="$2"; shift; shift;;
    -h | --help ) HELP=true; shift ;;
    -- ) shift; break ;;
    * ) break ;;
  esac
done

if [[ ${HELP} = true ]] || [ -z "${url}" ];  then
  usage
  exit 0
fi

# Check for impossible parameter combination ie. too many checks and delays in given time limit
if (( delay * count > time)); then
  echo -e "\e[31m### Error! The time ($time) provided is too short given the delay ($delay) and count ($count)\e[0m"
  exit 1
fi

echo -e "\n\e[36m### Polling \e[33m$url\e[36m for ${time}s, to get $count OK results, with a ${delay}s delay\e[0m\n"

# Generate tmp filename
tmpfile=$(echo "$url" | md5sum)

# Main loop 
while [ "$isUp" != "true" ]
do
  # Break out of loop if max time has elapsed
  if (( elapsed >= time )); then break; fi
  timestamp=$(date "+%Y/%m/%d %H:%M:%S")
  
  # Main CURL test, output to file and return http_code 
  urlstatus=$(curl -o "/tmp/$tmpfile" --silent --write-out '%{http_code}' "$url")

  if [ "$urlstatus" -eq 000 ]; then 
    # Code 000 means DNS, network error or malformed URL
    msg="\e[95mSite not found or other error"
  else
    if (( urlstatus >= 200 )) && (( urlstatus < 300 )); then
      # Check returned content with grep if check specified
      if [ -n "$search" ]; then
        # Only count as a success if string grep passed
        if grep -q "$search" "/tmp/$tmpfile"; then
          (( okCount=okCount + 1 ))
          msg="✅ \e[32m$urlstatus 🔍 Content check for '$search' passed"
        else
          msg="❌ \e[91m$urlstatus 🔍 Content check for '$search' failed"
        fi
      else
        # Good status code
        ((okCount=okCount + 1))
        msg="✅ \e[32m$urlstatus "
      fi

      if (( okCount >= count )); then isUp="true"; fi
    else
      # Bad status code
      msg="❌ \e[91m$urlstatus "
    fi
  fi

  # Output message + timestamp then delay
  echo -e "### $timestamp: $msg\e[0m"
  # if isUp false then delay
  if [ "$isUp" != "true" ]; then sleep "$delay"; fi
  ((elapsed=elapsed + delay))
done

rm "/tmp/$tmpfile" > /dev/null 2>&1
# Final result check
if [ "$isUp" == "true" ]; then
  echo -e "\n\e[32m### Result: $url is UP! 🤩\e[0m"
  exit 0
else
  echo -e "\n\e[91m### Result: $url is DOWN! 😢\e[0m"
  exit 1
fi