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Lab 5.1 - question concerning Linux 'cut' command

jcremp77
jcremp77 Posts: 37
in LFS258 Class Forum

Hi- This is not a show stopper, but I have done considerable research to understand this command. Just looking to understand this.
1. export client=$(grep client-cert $HOME/.kube/config |cut -d" " -f 6)
From what I have researched I understand the -d flag to indicate a delimiter of a blank space following the text 'client-cert' from where to begin the cut operation; however when looking into the -f flag, all I could find were examples using .csv files. If -f is for 'field', I am not quite sure what field 6 indicates. I understood examples that referenced .csv files, but kind of lost here. Any explanation to this would be greatly appreciated.

Comments

  • chrispokorni
    chrispokorni Posts: 2,012
    edited April 2021

    Hi @jcremp77,

    Ideally, this kind of question would be posted and answered in a Linux course related forum :wink:

    Assuming your content is field1,field2,field3, running cut -d "," -f 2 yields "field2".
    Assuming your content is field1 field2 field3, running cut -d " " -f 2 yields "field2" as well.

    What do you think happens, if your delimiter is one blank space (just like the second example above -d " ") and your fields were not equally delimited by single spaces, such as field1 field2 field3 (there should be 5 blank spaces between the first two fields and 1 single blank space between the last two fields). Try running the same command cut -d " " -f 2 and see if the output makes sense. Change the value of -f until you see a significant change in the output. Can you explain what caused the change? Was the change expected at all?

    EDIT: For some reason the 5 blank spaces are compressed into 1 single space, but try it either way by typing out the fields and leave 5 spaces between the first two.

    Regards,
    -Chris

  • jcremp77
    jcremp77 Posts: 37
    edited April 2021

    Hi @chrispokorni ,

    I am not sure I can articulate it well but I understand why the following is expected (text separated by 5 spaces)
    Note: used for the same reason you mentioned in your reply

    1. field1<5spc>field2<5spc>field3, running cut -d " " -f 2 results in "blank"
    2. field1<5spc>field2<5spc>field3, running cut -d " " -f 6 results in "field2"
    3. field1<5spc>field2<5spc>field3, running cut -d " " -f 11 results in "field3"

    For a single file with 3 rows (1st row separated by 1 space, 2nd by 2, and 3rd by 3)

    #start of file
    field1<1spc>field2<1spc>field3
    field1<2spc>field2<2spc>field3
    field1<3spc>field2<3spc>field3
    #end of file

    If running 'cut -d " " -f 3' on the file above the result would be:


    field3
    field2
    <blank>

    In the above '-f 3' indicates that what follows the 2nd " " will be output for every line in the file; hence the 3rd line returning nothing because 'field1' and 'field2' are separated by 3 " "'s; but '-f 4' would return:


    <blank>
    <blank>
    field2

    Thank you for taking the time to give an explanation to the following command:

    export client=$(grep client-cert $HOME/.kube/config |cut -d" " -f 6)

    Now if the above command had the value of "-f" were changed to 5, then the following output would be:

    client-certificate-data:

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