this post was submitted on 29 Jan 2025
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12
How can I use line continuations in GNU awk? (feddit.org)
submitted 2 days ago by [email protected] to c/[email protected]
10 comments fedilink hide all child comments
 

For a reason not worth mentioning here, I would like to write a somewhat more complex awk script in which I would have to explain in detail what I am doing. (If only so that I'll still know next week.) There doesn't seem to be a way to wrap a list of conditions in GNU awk, right?

This is what I tried:

command-that-prints-a-table | awk '
    NR>1 &&                # Skip line 1
    NF>2 &&                # Skip lines with only one column
    substr($1,1,1) != "("  # Skip lines that start with a "("
    { print $1 }
'

Alas, that does not work - awk skips the conditions entirely and only runs print $1. It seems that escaping the newlines does not work either, which makes sense as the end of the lines are comments.

This would work:

command-that-prints-a-table | awk '
# - Skip line 1
# - Skip lines with only one column
# - Skip lines that start with a "("
    NR>1 && NF>2 && substr($1,1,1) != "("  { print $1 }
'

But - my original code has a few more conditions - it is rather annoying to read and maintain. Is there an elegant way to fix this?

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[–] [email protected] 5 points 2 days ago (1 children)

You're probably best off writing the awk script in its own file instead of straight on the command line. Then you can comment to your heart's content without shell limitations. If you really want to do it inline, you might be able to do a $(# comment in a subshell). I remember doing something like that in the past, but I'm not near a computer to check right now.

[–] [email protected] 2 points 2 days ago

Thank you, the subshell idea is a good one!

[–] [email protected] 1 points 2 days ago* (last edited 2 days ago) (1 children)

If you're talking specifically about bash-compliant shells, just use a backslash.

[–] [email protected] 1 points 2 days ago (1 children)

Wouldn’t the backslash be a part of the comment?

[–] [email protected] 2 points 2 days ago* (last edited 2 days ago) (1 children)

It a line continuation like so:

printf "This is going to be a really \ long line that I want to break \ into different segments"

I'm seeing references that this is supposed to work elsewhere as well.

[–] [email protected] 1 points 2 days ago (1 children)

Sure, but that's inside a string:

$ printf "This is a   # let's break \
> long line."
This is a   # let's break long line.

awk remains unimpressed:

$ echo "This is a test.
> It has three lines, so I can
> test awk on it." | awk '
> NR>2    # Skip two lines. \
> { print $2 }   # should only print "awk"
> '
is
has
test awk on it.
awk
[–] [email protected] 1 points 2 days ago* (last edited 2 days ago) (1 children)

It works with long commands as well. Thinking in awk though, I would only use it after a statement is complete. You wouldn't be able to split up expressions like this, but if you're just talking about making it more readable, it should work.

Backslash works for long commands as well, but it's not going to split up an expression or string properly.

Works: apt install package1 \ package2 \ package3

Won't work: apt install pack\ age1 package2 pack\ age3

You can get cleaner code by substituting content blocks as variables, or piping EOF in and out at various places as other options.

[–] [email protected] 1 points 2 days ago (1 children)

You wouldn’t be able to split up expressions like this

Ah, that already answers my original question. A pity!

[–] [email protected] 1 points 2 days ago (1 children)

If cleaner is all you want, and you don't specifically care about the tool, maybe look at pyp

[–] [email protected] 3 points 2 days ago

Ah, I could probably use Perl or something as well. I was hoping awk could do it though. But thank you, I hadn't heard about pyp before!