Re: "sed" question

On 09.03.2024 13:27, 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.

Part of the joy programming in Awk. ;-)

You can't have an action without
enclosing braces.  But it's still legal syntax because...

it's an expression serving as a pattern.

This is the key observation!
Here we have only a condition in the general    condition { action }

The assignment itself is a side effect.

Assignments generally have a side effect, inherently. :-)

 Care needs to be taken when using this shortcut so the expression
doesn't evalute as false:

I've carefully formulated "In this specific case of regular data ..."

 $ 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=""'
$ 

Other questions on the data may be whether...
- the article number list may contain spaces
- the space after the colon is always existing
- blank lines may be existing in the file
- comment lines are possible in the file
These all will require a more "complex" awk pattern or action, yet
still simply solvable. Maybe something like
  BEGIN { FS=":[[:space:]]*" }
  !NF || /^[[:space:]]*#/ || $0=$1": 1-1"
Janis