Use awk to print the last N columns of a file or a pipe


In this post we will describe a way to print the last N number of columns in awk.

We will use this code as example, where we will print the last 2 columns only:

awk '{n = 2; for (--n; n >= 0; n--){ printf "%s\t",$(NF-n)} print ""}';
'

In the awk script we use the variable n to control how many columns we want to print. In the above example we initialized it  to the value 2 as that is the number of columns we want printed.

After, we use a for loop to iterate over the fields (in this case the last two fields) and we print them to the screen using printf "%s\t",$(NF-n) to avoid printing the new line character and to separate them with a tab character.

NF is a special variable in awk that holds the total number of fields available on that line. If you do not change the delimiter, then it will hold the number of words on the line.

$(NF-n) is the way we ask awk to gives us the variable value that is n places before the last.

Outside the loop we print "" to print the new line character between input rows.

Examples:

If we want to print the last two columns of the ls -l command we can do it as follows:

ls -l | awk '{i = 2; for (--i; i >= 0; i--){ printf "%s\t",$(NF-i)} print ""}';

If we want to print the last two columns of the /etc/passwd file we can do it as follows:

awk -F ':' '{i = 2; for (--i; i >= 0; i--){ printf "%s\t",$(NF-i)} print ""}' /etc/passwd;

Note that we change the delimiter with the command line argument -F ":"

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