Bash

Commonly used commands

If you want to see which commands you run often you can run the following command and you can even add in your .bashrc as an alias.

history | awk '{print $2}' | sort | uniq -c | sort -rn | head

See the largest directories in your current directory

This command will allow you to view 10 largest directories in your current directory.

du -hs */ | sort -hr | head

See which apps are talking on your network

This command allows you to see what apps are consuming internet.

ss -p

Replace words in a file using 'sed'

# To replace the word quinn in a file with target_env
$> sed -i 's/quinn/target_env/g' file_path

# To replace the word quinn in multiple files
$> sed -i 's/quinn/target_env/g' *

Get the current directory of a script being called

# Option 1:
SCRIPT_DIR="$(dirname "$(readlink -f "$0")")"

# Option 2:
SCRIPT_DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" &> /dev/null && pwd )"

Check if a list is empty

if [[ ${#list[@]} -eq 0 ]]; then
  echo "List is empty"
fi

Iterate of a list (for loop)

for i in "${list[@]}"; do
  echo "$i"
done
## Make sure the current user is root

```bash title="Make sure the current user is root"
if [[ $EUID -ne 0 ]]; then
   echo "This script must be run as root"
   exit 1
fi

Check if a command exists

if ! command -v docker &> /dev/null
then
    echo "Docker could not be found"
    exit
fi

Check if a file exists

if [ -f "$FILE" ]; then
    echo "$FILE exists."
else
    echo "$FILE does not exist."
fi

Check if a directory exists

if [ -d "$DIRECTORY" ]; then
    echo "$DIRECTORY exists."
else
    echo "$DIRECTORY does not exist."
fi

Check if a variable is empty

if [ -z "$var" ]
then
      echo "\$var is empty"
else
      echo "\$var is NOT empty"
fi

Check if a variable is not empty

if [ -n "$var" ]
then
      echo "\$var is NOT empty"
else
      echo "\$var is empty"
fi

Check if a variable is set

if [ -z ${var+x} ]; then echo "var is unset"; else echo "var is set to '$var'"; fi

Set a timeout for a command

timeout 10s command

Check if a command is running

if pgrep -x "command" > /dev/null
then
    echo "Running"
else
    echo "Stopped"
fi

Timestamps

# Timestamp in seconds
date +%s

# Timestamp in milliseconds
date +%s%3N

# Timestamp with formatting, i.e 20240104_121201
$(date +%Y%m%d_%H%M%S)

Get filename without extension

filename=$(basename -- "$fullfile")
extension="${filename##*.}"
filename="${filename%.*}"

String to lowercase

echo "HELLO" | tr '[:upper:]' '[:lower:]'

User commands

# Prints out the users who are currently logged in
who

# Prints out the users and how many are connected, can use -q or --count
who --count

# Prints out the users who are currently logged in and what they are doing
w

# This will kill the user section who's tty is pts/0
pkill -9 -t pts/0

# This will print out your current tty
tty

View process resources

# This will print out the resources for the current process
ps -o %cpu,%mem -p $$

# For a high level view of the resources being used by processes
top

# For a high level view of the resources being used by processes, but only show the processes for the current user
top -u $USER

# For a high level view of the resources being used by processes, but only show the processes for the current user and sort by memory usage
top -u $USER -o %MEM

# For a high level view of the resources being used by processes, but only show the processes for the current user and sort by cpu usage
top -u $USER -o %CPU

# To view the resources being used by a specific process
top -p $PID
# or
top -p `pgrep "process_name"`

Delete files older than x

find /path/to/files* -mtime +5 -delete

# This will delete files older than 5 days, but not in the directory /path/to/keep
find /path/to/files* -mtime +5 -not -path "/path/to/keep/*" -delete

find /path/to/files* -mmin +5 -delete