Loops and Ifs - Shell Script

Loops

Bash supports several types of loops, e.g., for, while e until.

for loop

The for loops will iterate until through a set of values in a list.

for i in $( ls )
do
  echo item: $i
done

In this case, the list is the result of executing the command ls, which returns the list of files and directories in the current directory. And the for loop iterates over all results printing each step using echo.

while loop

The while loop runs until the expression is false

#!/bin/bash 
I=0
while [ $I -lt 10 ]
do
  echo The counter is $I
  let I=I+1 
done

In this case, we have a variable I that starts with the value 0 and a while loop that runs until the expression I < 10 is false.

Case

do
  case $VAR in
  val1)
    echo "case val1"
    ;;
  val2)
    echo "case val2"
    ;;
  *)
  echo "Ups default result"
  ;;
esac

Ifs

if [ $VAR == "hello" ]
then
  echo hi
elif [ $VAR == "hello there" ]
then
  echo General Kenobi
else
  echo ...
fi

Useful Links:

• Loops
• Case
• Ifs