03-Loops-For.md

Loops

• Loops is used for repetative tasks, lets understand how it works in this lecture

Type of Loops

• for loops is used when you want to run same command multiple times

• Execute a command or a set of commands many times

• Iterate through files

• Iterate through lines within a file

• Iterate through the output of a command

• for loops can be written in multiple ways:

  for mission in <list of missions>
  do
    create-and-launch-rocket $mission
  done
  

  for mission in 1 2 3 4 5 6
  do
    create-and-launch-rocket $mission
  done
  

  for mission in {0..100}
  do
    create-and-launch-rocket $mission
  done
  

  

• Real life use case can be:

• Iterate thorugh list of files from the output of the ls command

• Iterate thorugh list of packages store them in a file and installs them one by one.

• ssh to the list of servers and check there uptime .

  for file in $(ls)
  do
   echo Line count of $file is $(cat $file | wc -l)
  done
  

  for server in $(cat servers.txt)
  do
   ssh $server "uptime"
  done
  

  for package in $(cat install-packages.txt)
  do
   sudo apt-get –y install $package
  done