For Loop | Shell Scripting

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This is a multipart blog article series where I am going to explain the concepts of shell scripting and how to write a shell script in Linux, UNIX or Mac based systems. You can also follow this tutorial blog using windows but for that you have to install a bash from.

In this article we are going to understand for loop in shell scripting.

  1. The syntax for loop. There are many ways to write the for loop.
    • First way
        for <variable_name> in 1 2 3 4 5 . . N
        do
            command1
            command2
            command3
        done
      
    • Second way
        for <variable_name> in file1 file2 file3
        do
            command1 on $<variable_name>
            command2
            commandN
        done
      
    • Third way
        for <variable_name> in $(Linux-Or-Unix_Command_Here)
        do
            command1 on $<variable_name>
            command2 on $<variable_name>
            commandN
        done
      
    • Forth way
        for (( EXP1; EXP2; EXP3 ))
        do
            command1
            command2
            command3
        done
      
  2. We can give the range to iterate like this {1..10}. Here the range is from 1 to 10
  3. If we want to specify increment than we can do that in this way {1..10..2}. Here the range is from 1 to 10 and increment will be of 2
  4. You can use the above methods only if your bash version is above 4.0. You can check you bash version by this command echo ${BASH_VERSION}

Reference code file for this article

So this was a brief introduction of for loop. Hope you liked it and learned something new form it.

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