This code prints "yes" in 4.1

awk 'BEGIN{token = "firstname"; if(token ~ (/^lastname|^firstname/)) {print "yes"} }'

...and in 5.1 prints nothing

The code is user error, there should be no parens around the //.

It's confusing why the versions have different results. Did 4.1 auto-detect the problem?

In article <c4685425-7035-4a1d-8948-8c1a8bbe2b9cn@googlegroups.com>,
Mary Karr <karrmary922@gmail.com> wrote:
>This code prints "yes" in 4.1
>
> awk 'BEGIN{token = "firstname"; if(token ~ (/^lastname|^firstname/)) {print "yes"} }'
>
>..and in 5.1 prints nothing

Confirmed. In 4.1.4, it prints "yes"; in 5.0.1 it prints nothing.

>The code is user error, there should be no parens around the //.
>
>It's confusing why the versions have different results. Did 4.1
>auto-detect the problem?

Actually, it looks like it is a bug fixed in 5.x.
The previous (4.x) behavior is actually incorrect.

Here's my explanation (which you may or may not already know). Basically,
AWK (specifically, GAWK) tries very hard to come up with a legal
interpretation of whatever you throw at it. Kind of like when a human
says something nonsensical to you; you try very hard to come up with an
interpretation of what they said that makes sense. Only if that is not
possible do you tell them that they are speaking gibberish.

What is happening is that when you put a bare regular expression in parens,
it then gets evaluated as either 0 or 1, depending on whether or not the
reg exp matches (i.e., is contained in) $0. The following demonstrates how
to change your program so that a current version of GAWK will print "yes":

$ /usr/bin/gawk 'BEGIN{$0="lastname";token = "first1ame"; if(token ~ (/^lastname|^firstname/)) {print "yes"} }'
yes
$

--
Mike Huckabee has yet to consciously uncouple from Josh Duggar.

On 2023-05-29, Kenny McCormack <gazelle@shell.xmission.com> wrote:
> What is happening is that when you put a bare regular expression in parens,
> it then gets evaluated as either 0 or 1, depending on whether or not the
> reg exp matches (i.e., is contained in) $0. The following demonstrates how
> to change your program so that a current version of GAWK will print "yes":

Awk is "weird" that way. Ostensibly, it is based on C, but brings
in various quirks, includiing whitespace sensitivities in the middle
of expressions.

In C, parentheses are sanely behaved. Given:

int x = 42;

These are valid:

(x)++;

(x) = (x) + 1;

Parentheses influence associativity and precedence. Other than that,
(x) is exactly the same as x to the point that if x is an lvalue,
so is x, and we can "increment through" and "assign through"
the parentheses.

Not so in Awk, or not all the time.

For instance, try this

BEGIN { (x) = 42; }

Nope! No "assigning through parentheses".

You cannot randomly sprinkle parentheses around expression terms in Awk.

--
TXR Programming Language: http://nongnu.org/txr
Cygnal: Cygwin Native Application Library: http://kylheku.com/cygnal
Mastodon: @Kazinator@mstdn.ca

In article <20230529111746.484@kylheku.com>,
Kaz Kylheku <864-117-4973@kylheku.com> wrote:
>On 2023-05-29, Kenny McCormack <gazelle@shell.xmission.com> wrote:
>> What is happening is that when you put a bare regular expression in parens,
>> it then gets evaluated as either 0 or 1, depending on whether or not the
>> reg exp matches (i.e., is contained in) $0. The following demonstrates how
>> to change your program so that a current version of GAWK will print "yes":
>
>Awk is "weird" that way. Ostensibly, it is based on C, but brings
>in various quirks, includiing whitespace sensitivities in the middle
>of expressions.

Note, BTW, that if you change the slashes to quotes - i.e., put:

token ~ ("^lastname|^firstname"))

the problem goes away (though other problems may appear).

--
The key difference between faith and science is that in science, evidence that
doesn't fit the theory tends to weaken the theory (that is, make it less likely to
be believed), whereas in faith, contrary evidence just makes faith stronger (on
the assumption that Satan is testing you - trying to make you abandon your faith).

On 30.05.2023 00:20, Kenny McCormack wrote:
> In article <20230529111746.484@kylheku.com>,
> Kaz Kylheku <864-117-4973@kylheku.com> wrote:
>> On 2023-05-29, Kenny McCormack <gazelle@shell.xmission.com> wrote:
>>> What is happening is that when you put a bare regular expression in parens,
>>> it then gets evaluated as either 0 or 1, depending on whether or not the
>>> reg exp matches (i.e., is contained in) $0. The following demonstrates how
>>> to change your program so that a current version of GAWK will print "yes":
>>
>> Awk is "weird" that way. Ostensibly, it is based on C, but brings
>> in various quirks, includiing whitespace sensitivities in the middle
>> of expressions.
>
> Note, BTW, that if you change the slashes to quotes - i.e., put:
>
> token ~ ("^lastname|^firstname"))
>
> the problem goes away (though other problems may appear).

Other problems than those inherent to dynamic regexps? - Looks fine to me.

Janis