Re: "sed" question

On 3/9/2024 6:27 AM, Christian Weisgerber wrote:

On 2024-03-06, Janis Papanagnou <janis_papanagnou+ng@hotmail.com> wrote:
 

$ awk '{print $1, "1-1"}'  newsrc-news.eternal-september.org-test >
newsrc-news.eternal-september.org

>
In this specific case of regular data you can simplify that to
>
   awk '$2="1-1"'  sourcefile > targetfile

 That had me scratching my head.  You can't have an action without
enclosing braces.  But it's still legal syntax because... it's an
expression serving as a pattern.  The assignment itself is a side
effect.
 Care needs to be taken when using this shortcut so the expression
doesn't evalute as false:

About 20 or so years ago we had a discussion in this NG (which I'm not going to search for now) and, shockingly, a consensus was reached that we should encourage people to always write:
     '{$2="1-1"} 1'
instead of:
     $2="1-1"
unless they NEED the result of the action to be evaluated as a condition, for that very reason.
     Ed.

 $ printf 'one 1\ntwo 2\nthree 3\n' | awk '$2=4'
one 4
two 4
three 4
$ printf 'one 1\ntwo 2\nthree 3\n' | awk '$2=0'
$
 $ printf 'one 1\ntwo 2\nthree 3\n' | awk '$2="4"'
one 4
two 4
three 4
$ printf 'one 1\ntwo 2\nthree 3\n' | awk '$2=""'
$