About this project

I'm a fairly new developer without much knowledge of bash and was hoping make a small bash script. I have a background in c++ and javascript and wanted a quick format guide that would take me from those languages to the bash equivalents.

I started just trying to wing it myself but had a little trouble. So, I googled it to find out more and had a hard time finding a quick "Cheatsheet" showing the proper syntax. So, I thought, why not make one.

So I've tried to curate a few resources and pull the information to make a complete beginner's guide.

I hope to include example scripts eventually that you can download and just take and modify. For now though, it's just this simple guide.

It's a rough piece of work but hopefully it provides some usefulness to someone.

Enjoy!

Basics

Start files with: #!/bin/bash

Comments: #This is a comment

create a variable: VARIABLE="hello world"

NOTE: You cannot have spaces around the "=" sign. If you do it won't evaluate.

reference a variable: $VARIABLE

Command Line Arguments

Name of the script: $0

1st command argument: $1

2nd command argument: $2

etc.

get output from a command

#!/bin/bash
OUTPUT="hello world"
OUTPUT="$( ls )"
echo $OUTPUT

This program sets OUTPUT to "hello world". It then re-sets it to the ouput of the command ls. So in the end, this script will print out the output of ls, not "hello world".

Basic Commands

Read input and into variable read VARIABLE

Print out to the console echo "Hello World" or printf "Hello World"

Print out to a file echo "Hello World" >> path/to/file

Delay for 1 second sleep 1

Conditional Statements:

if statements

#basic case
if [ "foo" = "foo" ];
  then
    echo "these are equal"
fi

# Use parentheses when working with integers
if (($COUNT < 10))
  then
    echo "Numbers are equal"
fi

# Use square-brackets when working with strings
if [[ $VARIABLE = "string" ]]
  then
    echo "Strings are equal"
fi

if else block

if [[   ]]
    then
      echo "true"
  elif [[   ]]
    then
      echo "also true"
  else
      echo "false"
fi

case statements

case $1 in
  "string1")
    echo "1st condition met"
    ;;
  "string2")
    echo "2nd condition met"
    ;;
  *)
    echo "This is the 'default' case"
  ;;
esac

Loops

while loops

while runs the loop while the condition is true

#basic while true loop
while true
  do
    echo "Infinite loop"
done

until loops

until runs the loop until the condition is true (i.e. while the condition is false).

COUNT=0
until ((COUNT > 10))
do
  echo "$COUNT"
  ((COUNT ++))
done
echo "Outside until loop"

for loops

c++ type for loops are done with a counter and a while loop.

#for type while loop
COUNT = 10
while(( COUNT > 0))
  do
    echo "$COUNT"
    ((COUNT --))
done
echo -e "\n\nFIRE!!"

for each loops

bash for loops iterate through a list of objects and perform an action for each item.

for F in $(ls)
do
  [! -f $F] && continue
  DT=$(stat $F)
  echo ""
done

Functions

function_name () {
    command...
}

Resources

Beginner's Guide

How To Guide

Youtube Tutorials

dansteren/bash-cheat-sheet