Regex with backslashes in a collection

[JohnBeckett]

I'm using Vim 8 or 9 with 'magic' and re=0 (same using re=1).

I want to find "\[" or "\]" in text like:
abc\[def\]ghi\\xy\z

The following pattern also find the two backslashes.
\\[\[\]]

Help says that a backslash in a collection (if not followed
by certain characters) just means a backslash.
:help /\]

Why does the pattern find two backslashes (but not one)?

These patterns find only "\]" (good):
\\[\]]
\\[]]

But this finds "\[" and "\\" (not "\"):
\\[\[]

John

[aro...@vex.net]

> I'm using Vim 8 or 9 with 'magic' and re=0 (same using re=1).
>
> I want to find "\[" or "\]" in text like:
> abc\[def\]ghi\\xy\z
>

The problem may lie in the boundary of a character class, [ and ] and the
rules about its content.
Does the regex interpreter read [\[] as 2 characters, "\ or ]" or as one
"literal ]"; or "literal \"? How is the following "]" parsed?

There may be enough ambiguity in the definitions that tests will only be
valid in the particular interpreter.

[Gary Johnson]

On 2022-08-13, arocker wrote:
> > I'm using Vim 8 or 9 with 'magic' and re=0 (same using re=1).
> >
> > I want to find "\[" or "\]" in text like:
> > abc\[def\]ghi\\xy\z
> >
>
> The problem may lie in the boundary of a character class, [ and ] and the
> rules about its content.
> Does the regex interpreter read [\[] as 2 characters, "\ or ]" or as one
> "literal ]"; or "literal \"? How is the following "]" parsed?

According to ":help /\]", [\[] is a collection containing two
characters, \ and [.

Regards,
Gary

[JohnBeckett]

> [\[] is a collection containing two characters, \ and [

Yes, that's what my test shows. The problem is that the pattern \\[\[] finds "\\" and "\[" but not "\".

John

[Tommy Bollman]

/\(\\[\|\\\]\)

No magic or anything set as you can see. Matches \[ or \]. 

Regards.

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[Gary Johnson]

Right. Your pattern says to find a \ followed by one of the
items of the collection containing \ and [. So, it will match
either of

\\
\[

but not a single \ unless it is immediately followed by a [. If you
want it to also match a single \, you could use this:

\\[\[]\?

which will match \ followed by zero or one of \ or [.

Regards,
Gary