How do I make a regular expression email watch filter for this string
please?

[OpenSCAD]

Both of the following gave the syntax error. I expected the second to
work as I thought I had correctly 'escaped' the square brackets.

Subject: [OpenSCAD]
Subject: \[OpenSCAD\]

Terry

OK thanks, after a refresher in Help and some trial/error I got it.

I actually meant to ask 'How do I make a normal (Agent) expression email
watch filter ...' I now assume the answer would have been that I could
not do so. Anyway my solution is this REGULAR expression:
Subject: {\[OpenSCAD\]}

(I think 'Regular' is an unfortunate adjective to describe these obscure
syntax expressions.)

Terry Pinnell <me@somewhere.invalid> wrote:

>How do I make a regular expression email watch filter for this string
>please?
>
>[OpenSCAD]
>
>Both of the following gave the syntax error. I expected the second to
>work as I thought I had correctly 'escaped' the square brackets.
>
>Subject: [OpenSCAD]
>Subject: \[OpenSCAD\]
>
>Terry

On Fri, 09 Jul 2021 15:09:06 +0100, Terry Pinnell
<me@somewhere.invalid> wrote:

>(I think 'Regular' is an unfortunate adjective to describe these obscure
>syntax expressions.)

The term dates from the 1951 when computer science was inventing
languages. It has its origin in the mathematics of computer theory and
symbolic logic. The term applies because the syntax and meaning were
"regular" as defined by the language in use. Ken Thompson built on the
idea when developing B and C languages and it entered common use on
Unix in vi, sed, awk and other tools. We're stuck with it.

Terry Pinnell schrieb:

> How do I make a regular expression email watch filter for this string
> please?
>
> [OpenSCAD]

Regular expressions in Agent have to be enclosed in curly braces, so:
| Subject: {\[OpenSCAD\]}

Without escaping the square brackets the expression would match any
subject containing at least one of the characters in those brackets,
as "[...]" defines a character range.

> Both of the following gave the syntax error. I expected the second to
> work as I thought I had correctly 'escaped' the square brackets.
>
> Subject: [OpenSCAD]
> Subject: \[OpenSCAD\]

Outside of regular expressions, i.e. without curly braces, square
brackets stand for a range of numbers in Agent's expression language,
like "[10,100]", so only digits are allowed between square brackets.

Regards,
-thh

Geoff <geoff@invalid.invalid> wrote:

>On Fri, 09 Jul 2021 15:09:06 +0100, Terry Pinnell
><me@somewhere.invalid> wrote:
>
>>(I think 'Regular' is an unfortunate adjective to describe these obscure
>>syntax expressions.)
>
>The term dates from the 1951 when computer science was inventing
>languages. It has its origin in the mathematics of computer theory and
>symbolic logic. The term applies because the syntax and meaning were
>"regular" as defined by the language in use. Ken Thompson built on the
>idea when developing B and C languages and it entered common use on
>Unix in vi, sed, awk and other tools. We're stuck with it.

Thanks Geoff, understood. Analogous to 'regular polygon' etc.

Terry

Thomas Hochstein <thh@thh.name> wrote:

>Terry Pinnell schrieb:
>
>> How do I make a regular expression email watch filter for this string
>> please?
>>
>> [OpenSCAD]
>
>Regular expressions in Agent have to be enclosed in curly braces, so:
>| Subject: {\[OpenSCAD\]}
>
>Without escaping the square brackets the expression would match any
>subject containing at least one of the characters in those brackets,
>as "[...]" defines a character range.
>
>> Both of the following gave the syntax error. I expected the second to
>> work as I thought I had correctly 'escaped' the square brackets.
>>
>> Subject: [OpenSCAD]
>> Subject: \[OpenSCAD\]
>
>Outside of regular expressions, i.e. without curly braces, square
>brackets stand for a range of numbers in Agent's expression language,
>like "[10,100]", so only digits are allowed between square brackets.
>
>Regards,
>-thh

Thanks, understood. As you see up-thread I finally got there myself a
while after posting ;-)

Also went searching for a list of special characters in this context,
That's usually the main cause of my hesitation on the infrequent
occasions I make a filter. In case it's of help to anyone who ends up
here with a similar query I'll paste below. Note that I haven't checked
it 100% for accuracy to Agent; it was from a post in the forum of my
text editor, TextPad.

--------------------
These characters are not special in regular expressions and can be used
literally:
Code:
: ,
_ '
; "
<
>
/ ~

These characters are special in regular expressions and (in most cases)
must be quoted, either by prefixing them with a backslash (\) or by
turning them into a character class by enclosing them in square brackets
([..]).:
Code:
$ ?
* +
( )
[ ]
{ }
| ..

These characters are special in regular expressions and must be quoted
by prefixing them with a backslash (\) whether or not they are in a
character class:
Code:
^ \
--------------------

Terry