Shell Programming and Scripting

Trying to understand below;

what is this do? NR==3{li=$0"|"li}


a=$(awk 'BEGIN{li=""}NR==1||NR==3{li=$0"|"li}END{print li}' "file")

NR==1||NR==3{li=$0"|"li} If it is first or third line, then concatenate that row data with value in variable li and store it in variable li.

so, basically, at the begining, put li value to null,

and if first or 3rd line, then... hmm I still dont' understand this part of
how {li=$0"|"li} equals concatenate that row(which is what's in 1st and 3rd line) with value in variable(which is null at this point? but I am assuming this becomes.. first line.. and then.. 3rd line ..

so value becomes 3rdline|1stline <-- separated by | ?

I thought $0 was the entire record.. how does assigning entire record to li becomes this meaning? can you elaborate little further please?



Originally Posted by convenientstore
Trying to understand below;

what is this do? NR==3{li=$0"|"li}


a=$(awk 'BEGIN{li=""}NR==1||NR==3{li=$0"|"li}END{print li}' "file")

NR==1||NR==3{li=$0"|"li} If it is first or third line, then concatenate that row data with value in variable li and store it in variable li.

You are correct.

$0 contain the current line read from the file.
Let us consider the following file

Code:

abc
def
ghi
jkl

For first line, li="abc" "|" ""
For the third line, li="ghi" "|" "abc|"