A collection of useful bash scripts

useful.sh

#!/usr/bin/env bash

# List files that exist only in dir1. https://stackoverflow.com/a/24695424/1902896
comm -23 <(ls dir1 | sort) <(ls dir2 | sort)  

# Find files with a certain name located in the specified directory
find <directory> -name "<file_name>" 2>/dev/null 

# Find files with a certain name located in the specified directory, then loop over each file name, printing each one. 

# This starts to run the loop as soon as `find` produces output on stdout.
find <directory> -name "<file name>" 2>/dev/null  | while read -r file; do
  echo "$file"
done

# This waits unil the `find` has completed before beginning to loop.
while read -r file; do
  echo "$file"
done <<< "$(find <directory> -name "<file name>" 2>/dev/null)"

# Prepend text to a file
echo 'task goes here' | cat - todo.txt > temp && mv temp todo.txt

# Clean up all non-running Docker things:
docker system prunt -a -f

# Parse JSON on the shell with `jq`:
<some command that outputs JSON to stdout> | jq '.key1.subkey1'

# Output the contents of a file with the 
cat -n <some_file>

# Global .gitignore file: 
# http://egorsmirnov.me/2015/05/04/global-gitignore-file.html
echo "\
.idea/
*.iml
*.iws
*.ipr
" >> ~/.gitignore_global && git config --global core.excludesfile ~/.gitignore_global

# Enable sources in /etc/apt/sources.list
sudo sed 's|# deb-src|deb-src|' -i /etc/apt/sources.list

# Find what package a command came from
type who
# output: who is /usr/bin/who
dpkg -S /usr/bin/who
# output: coreutils: /usr/bin/who

# Import a PGP public key using curl (gpg's http client is riddled with bugs):
curl -fsSL "https://keyserver.ubuntu.com/pks/lookup?op=get&options=mr&search=0x2EE0EA64E40A89B84B2DF73499E82A75642AC823" | gpg --import

# Normalizing line endings in a git repository:
git read-tree --empty   # Clean index, force re-scan of working directory
git add .
git status        # Show files that will be normalized
git commit -m "Introduce end-of-line normalization"

# Generate an Ed25519 key pair. https://medium.com/risan/upgrade-your-ssh-key-to-ed25519-c6e8d60d3c54
ssh-keygen -t ed25519

# Upload an arbitrary Jar file into a Maven repository
mvn deploy:deploy-file -DgroupId=come.wheeler -DartifactId=artifact-name -Dversion=1.0 -DgeneratePom=true -Dpackaging=jar -DrepositoryId=server-name-in-settings.xml -Durl=https://repository.host/artifactory -Dfile=jar-file.jar

# Determine if a OpenShift pod is ready:
until [ "$(oc get pods --selector strimzi.io/name=rtp-demo-cluster-entity-operator -o jsonpath='{.items[<number of pods>].status.containerStatuses[?(@.name == "<container name>")].ready}" 2>/dev/null)' = "true[ true]{<number of containers> - 1}" ]; do sleep 1; done

# Set everything to use Nano:
sudo update-alternatives --install /usr/bin/editor editor $(which nano) 1

# Redirect to stderr but also save to a variable
tee >(jq . | cat 1>&2) | jq -r .access_token

# Decode cron expressions
# https://crontab.guru

# Set Gnome to use sloppy focus
gsettings set org.gnome.desktop.wm.preferences focus-mode sloppy

# Some useful functions:
info() { echo "INFO:" "$@"; }
die() { rc=$?; (( $# )) && { for s in "$@"; do >&2 printf "ERROR: %s\n" "$s"; done; }; exit "$rc"; }
escape() { sed -e 's/[^^]/[&]/g; s/\^/\\^/g; $!a\'$'\n''\\n' <<< "$@" | tr -d '\n'; }
read_literal() { IFS= read -r -d '' "$1" || :; }

# Add usage information to a makefile
#help:  ## Display this help
#	@awk 'BEGIN {FS = ":.*##"; printf "\nUsage:\n  make \033[36m<target>\033[0m\n"} /^[a-zA-Z0-9_-]+:.*?##/ { printf "  \033[36m%-15s\033[0m %s\n", $$1, $$2 } /^##@/ { printf "\n\033[1m%s\033[0m\n", substr($$0, 5) } ' $(MAKEFILE_LIST)

# Do something in bash for a period of time and then quit either if it returns successfully or a timeout period expires.
# Timeout approach:
WAIT_TIME=10
check_func() {
  while :; do
    if curl www.example.com; then
      return 0
    fi
    sleep $SLEEP_TIME
  done
}
export -f check_func
trap 'kill -INT -$pid' INT
timeout $WAIT_TIME bash -c "check_func" &
pid=$!
wait $pid

# For-loop approach
WAIT_TIME=10
SLEEP_TIME=1
count="$(( WAIT_TIME / SLEEP_TIME ))"
for ((i=1; i<=count; i++)); do
  if curl www.example.com; then
    break
  fi
  sleep $SLEEP_TIME
done