Shell Script

File exists

With the if statement

FILE=/etc/resolv.conf
if [ -f "$FILE" ]; then
    echo "$FILE exists."
else 
    echo "$FILE does not exist."
fi

With the "&&" operator

[ -f /etc/resolv.conf ] && echo "File exists!"

Folder exists

if [ "$(ls -A /tmp)" ]; then
  echo "Exists and is not Empty"
fi

# Or using `-d`

if ! [ -d "/var/www/html" ] || ! [ -d "/var/www/x-html" ]; then
    echo "Folder not found here - ;("
fi

Or not exists

if ! [ "$(ls -A /tmp322)" ]; then
  echo "Empty"
else
  echo "Not Empty"
fi

Find differences between foldes

diff -q directory-1/ directory-2/

Show ports in use

sudo lsof -i -P -n | grep LISTEN

Create alias

Insert the line below to your ~/.zsh.rc or ~/.profile

alias ports="sudo lsof -i -P -n | grep LISTEN"

Cheatsheet of multiple commands

A; B    # Run A and then B, regardless of success of A
A && B  # Run B if and only if A succeeded
A || B  # Run B if and only if A failed
A &     # Run A in background.

Example

mv tmp.file tmp.file2 ; echo 'aa'
mv tmp.file tmp.file2 && echo 'aa'
mv tmp.file tmp.file2 || echo 'aa'
mv tmp.file tmp.file2 &

Read every line from a file

In the example below read every line from a file and do something.

while read line; do
  if [ ! -z $line ]; then
   echo "export $line" >> /etc/apache2/envvars
  fi
done <app.env

Log

Basic view of records

journalctl

To see the logs that the journald daemon has collected, use the journalctl command