for

• A for is used to loop through a set of values. The loop sets a variable to each value in the list and then the loop is executed once for each value.
• The basic format for a for-loop in shell is:

  for var in value1 value2 value3
  do
      command
      command
  done
  

• In shell, you may put as many statements inside the for as you would like.
• The do and the done are required, even if there is only one statement to execute.
• Inside the loop, the variable is set to each word.
• Here's an example:

  for i in 1 2 3 "the end"
  do
      echo "i is " $i
  done
  

  The output from running this for loop will be:

  i is 1
  i is 2
  i is 3
  i is the end
  

• Notice the values don't have to be numbers - it is just a list of values.
• If you want whitespace in one of the values, put it in double quotes, like "the end".

• You can also write a standard counting loop in bash (make sure N is set!):

  for (( i = 0 ; i < $N ; i++ ))
  do
      echo $i
  done

• If your loop uses hard-coded values to control the loop, you can use this syntax:

  for num in {1..10}
  do
      echo $num
  done

• This loop will set a variable called arg to each of the arguments passed into the shell script and then print each one on a line by itself:
  

• The "${@}" has special meaning to the shell. It means "all of the arguments, and maintain the original whitespace". Don't worry too much about it right now - just use it when your code needs to loop through all of the arguments.