Bash Scripting 101

Basics

• variables
• functions
• Loops
• Conditionals (If statements)
• taking user input
• check if a user is root
• check if a file or directory already exists
• colouring the output
• writing and redirecting data
• find your IP address
• find your hostname
• check if a package is already installed
• check if package dependencies are met
• how to make a link clickable
• exit if unmet dependencies/deps can’t be installed
• exit statuses (0-255, $?)
• $? exit status of last command
• logging
• wildcards
• looping over multiple arguments

echo

• When using echo -e use double quotation marks ” or it won’t work.
• When using variables inside a string, you need to encapsulate the string in double quotation marks ”
• When using If statements, always wrap your variables in double quotation marks “” to account for spaces in file/dir names
• Use \n in the beginning to give a line break between your response text and the command output
• http://stackoverflow.com/questions/13617843/unary-operator-expected
• you can check for exit statuses of multiple commands with ||. This can be used where you are unsure of which OS will be running the command

Find external IP

1SERVER_IP=`dig +short myip.opendns.com @resolver1.opendns.com` # External IP of the server

Multiple commands on the same line

You can put multiple commands on the same line by separating them with a semicolon ;

For example

1if [ “$?” -eq “0” ]; then
2  # do something
3fi

Make script executable

chmod +x foo.sh