Re: [bug-gawk] Is \x24 the literal dollar character?

[arnold]

Hi.

I looked into this. Please see the sidebar in that same section of the
manual that you cited:

| @sidebar Escape Sequences for Metacharacters
| @cindex metacharacters @subentry escape sequences for
| 
| Suppose you use an octal or hexadecimal
| escape to represent a regexp metacharacter.
| (See @ref{Regexp Operators}.)
| Does @command{awk} treat the character as a literal character or as a regexp
| operator?
| 
| @cindex dark corner @subentry escape sequences @subentry for metacharacters
| Historically, such characters were taken literally.
| @value{DARKCORNER}
| However, the POSIX standard indicates that they should be treated
| as real metacharacters, which is what @command{gawk} does.
| In compatibility mode (@pxref{Options}),
| @command{gawk} treats the characters represented by octal and hexadecimal
| escape sequences literally when used in regexp constants. Thus,
| @code{/a\52b/} is equivalent to @code{/a\*b/}.
| @end sidebar

In short, with --traditional, you'll get the behavior you're looking
for. Otherwise, gawk is following POSIX and treating such characters
as real metacharacters.

To solve your problem, you can do something like:

        gawk '$0 ~ ("\\$" "Id: .*" "\\$") {print}' <<< '$Id: rcsid$'

HTH,

Arnold

"Kozics Peter (FM)" <address@hidden> wrote:

> Dear,
>
>
> (1)
> this matches:
> $ gawk '/\$Id: .*\$/ {print}' <<< '$Id: rcsid$'
> $Id: rcsid$
>
> (2)
> I expected that this would match as well, but it didn't:
> $ gawk '/\x24Id: .*\x24/ {print}' <<< '$Id: rcsid$'
>
> The expectation was based on gawk manual section 3.2: \x24 should be
> the literal dollar character, not the dollar metacharacter.
>
> (3)
> Now, let's go on, this does not match either:
> $ gawk '/\\x24Id: .*\\x24/ {print}' <<< '$Id: rcsid$'
>
> (4)
> And this one still not:
> $ gawk '/\\\x24Id: .*\\\x24/ {print}' <<< '$Id: rcsid$'
>
> (5)
> At long last, this matches again:
> $ gawk '/\x5c\x24Id: .*\x5c\x24/ {print}' <<< '$Id: rcsid$'
> $Id: rcsid$
>
> which looks to me awkward and quite counterintuitive.  
>
> -------------
> The problem with (1) is that when the regexp is in a file under RCS
> control, RCS will destroy the regexp upon checkout by performing a
> keyword substitution. So the straightforward and seemingly manual-
> compliant solution would be (2), which is unfortunately not.
>
> I wonder if I found a gawk bug or a flaw in the regexp / literal / meta
> concept or a vague place in the gawk manual. Or just misunderstood
> something?
>
> -------------
> OS:
> $ uname -a
> Linux gygv 5.2.18-200.fc30.x86_64 #1 SMP Tue Oct 1 13:14:07 UTC 2019
> x86_64 x86_64 x86_64 GNU/Linux
>
> gawk:
> $ gawk --version
> GNU Awk 4.2.1, API: 2.0 (GNU MPFR 3.1.6-p2, GNU MP 6.1.2)
> Copyright (C) 1989, 1991-2018 Free Software Foundation.
>
> gawk manual:
> This is Edition 4.2 of GAWK: Effective AWK Programming
>
>
> yours
> KP
>