Cheatsheet Bash scripting

This cheatsheet will have more code snippets on how to do something in bash. It will be a bit different from some other cheatsheets where I show a list of commands.

Basics

• echo - print text to the terminal
  • echo Hello world! - prints 'Hello world!'

Variables

• COLOR="green" - create variable COLOR and set it to green, you can then use it such as:
  • echo $COLOR
  • echo "$COLOR"
  • echo "${COLOR}"
  • echo "My favourite color is $COLOR!"

Arrays

• COLORS=("red", "green", "blue") - Define an array of colors
• echo ${COLORS[0]} - Print first element in the array
• echo ${COLORS[-1]} - Print last element in the array
• echo ${COLORS[@]} - Prints all elements separated by a space
• echo ${#COLORS[@]} - Prints the number of elements in the array

Loops

For loops:

bashCopy
1for item in ${MYLIST[@]}; do
2  echo $item
3done

bashCopy
1for ((i=0; i < 10; i++)); do
2  echo $i
3done

bashCopy
1for i in {1..10}; do
2  echo "Iteration number: $i"
3done

While loop:

bashCopy
1while true; do
2  echo "HELLO!"
3done

Conditionals

Conditionals follow the familiar if statements:

bashCopy
1if [ $COLOR != "green" ]; then
2  echo "Your favourite color isn't green"
3fi

You can use [[ ... ]] to get a status of 0 or 1 depending on the evaluation of the conditional expression inside [[]].

• [[ -z STRING ]] - Empty string
• [[ -n STRING ]] - Not empty string
• [[ -e FILE ]] - File exists
• [[ -r FILE ]] - File is readable
• [[ -d PATH ]] - PATH is a directory
• [[ -w FILE ]] - File is writeable
• [[ -s FILE ]] - File size is larger than 0 bytes
• [[ -x FILE ]] - File is executable
• [[ STRING == STRING ]] - Both strings are equal
• [[ STRING != STRING ]] - Strings aren't equal
• [[ STRING =~ STRING ]] - Test STRING against a regex pattern
• [[ NUM -eq NUM]] - Both numbers are equal
• [[ NUM -ne NUM ]] - Numbers aren't equal
• [[ NUM -lt NUM ]] - First NUM is less than second NUM
• [[ NUM -le NUM ]] - First NUM is less or equal than second NUM
• [[ NUM -gt NUM ]] - First NUM is greater than second NUM
• [[ NUM -ge NUM ]] - First NUM is greater or equal than second NUM
• [[ ! EXPRESSION ]] - Not
• [[ EXPRESSION && EXPRESSION ]] - And
• [[ EXPRESSION || EXPRESSION ]] - Or

References

• Bash Reference Manual
• Devhints
• LearnXinYMinutes - Bash