Re: "sed" question

On 3/7/24 18:09, Keith Thompson wrote:

I know that's what awk does, but I don't think I would have expected it if I didn't know about it.

Okay.  I think that's a fair observation.

$0 is the current input line.

Or $0 is the current /record/ in awk parlance.

If you don't change anything, or if you modify $0 itself, whitespace betweeen fields is preserved.

If you modify any of the fields, $0 is recomputed and whitespace between tokens is collapsed.

I don't agree with that.
    % echo 'one  two   three' | awk '{print $0; print $1,$2,$3}'
    one  two   three
    one two three
I didn't /modify/ anything and awk does print the fields with different white space.

awk *could* have been defined to preserve inter-field whitespace even when you modify individual fields,

I question the veracity of that.  Specifically when lengthening or shortening the value of a field.  E.g. replacing "two" with "fifteen". This is particularly germane when you look at $0 as a fixed width formatted output.

and I think I would have found that more intuitive.

I don't agree.

(And ideally there would be a way to refer to that inter-field whitespace.)

Remember, awk is meant for working on fields of data in a record.  By default, the fields are delimited by white space characters.  I'll say it this way, awk is meant for working on the non-white space characters.   Or yet another way, awk is not meant for working on white space charters.

The fact that modifying a field has the side effect of messing up $0 seems counterintuitive.

Maybe.
But I think it's one that is acceptable for what awk is intended to do.

Perhaps the behavior matches your intuition better than it matches mine.

I sort of feel like you are wanting to / trying to use awk in places where sed might be better.  sed just sees a string of text and is ignorant of any structure without a carefully crafted RE to provide it.
Conversely awk is quite happy working with an easily identified field based on the count with field separators of one or more white space characters.
Consider the output of `netstat -an` wherein you have multiple columns of IP addresses.
Please find a quick way, preferably that doesn't involve negation (because what needs to be negated may bey highly dynamic) that lists inbound SMTP connections on an email server but doesn't list outbound SMTP connections.
awk makes it trivial to identify and print records that have the SMTP port in the local IP column, thus ignoring outbound connections with SMTP in the remote column.
Aside:  Yes, I know that ss and the likes have more features for this, but this is my example and ss is not installed everywhere.
I sort of view awk as somewhat akin to SQL wherein fields in awk are like columns in SQL.
I'd be more than a little bit surprised to find an SQL interface that preserved white space /between/ columns.  --  Many will do it /within/ columns.
awk makes it trivial to take field oriented output from commands and apply some logic / parsing / action on specific fields in records.

(And perhaps this should be moved to comp.lang.awk if it doesn't die out soon.

comp.lang.awk added and followup pointed there.

Though both sed and awk are both languages in their own right and tools that can be used from the shell, so I'd argue there's a topicality overlap.)

;-)
--
Grant. . . .