Обсуждение: Regular expressions syntax: is \ the escape character ?

Hi,

I'm using regular expressions in 6.5.3 version but i cannot find the
character to escape special caracters as ?, $, ^.

I've tried with \ but it doesn't works.

Example: i want to find the row with the value 'fisica?' and i do:

select title from libros where title ~* 'fisica\?' ;

but i also obtain rows with values:  'fisicamente' or 'fisicas'

What am i doing wrong ?

Thanks in advance.

Gabi :-)

You have to use two backslashes, as the preprocessor will take the first
one out (I may be wrong about this, but I remember reading something
similar a few months ago on this list.)  Also, remember that you have to
send two slashes to PostGres, which may mean that you need to use 4 slashes
in your code.  IE, for a PERL program:

$dbi->prepare("SELECT field FROM table WHERE field ~* '\\+'");

is actually only sending:
SELECT field FROM table WHERE field ~* '\+'
to the backend, so you should use:
$dbi->prepare("SELECT field FROM table WHERE field ~* '\\\\+'");




At 03:04 PM 3/3/00, Gabriel Fernandez wrote:
>Hi,
>
>I'm using regular expressions in 6.5.3 version but i cannot find the
>character to escape special caracters as ?, $, ^.
>
>I've tried with \ but it doesn't works.
>
>Example: i want to find the row with the value 'fisica?' and i do:
>
>select title from libros where title ~* 'fisica\?' ;
>
>but i also obtain rows with values:  'fisicamente' or 'fisicas'
>
>What am i doing wrong ?
>
>Thanks in advance.
>
>Gabi :-)
>
>
>************

Thanks a million to you all. Finally, as someone in the list suggested, i'm
using the double backslash (\\) and it seems it works ok.

The only problem i have is when i want to escape a single quote (') or the
backslash (\).

For example: i have one row with the value 'ONE\SECOND'

I try to recover it doing (from psql frontend):

select field1 from table1 where field1 ~* 'ONE\\\'  ;

But it doesn't work, and the parser seems to be confused (it asks me to
close again the quote ' ).

The problem is the same with the single quote '. I've tried this:

select field1 from table1 where field1 ~* 'D\\'ALEMA' ;

But it doesn't work neither.

Thanks for your help.

Gabi :-)

Gabriel Fernandez <gabi@unica.edu> writes:

> The only problem i have is when i want to escape a single quote (') or the
> backslash (\).
>
> For example: i have one row with the value 'ONE\SECOND'
>
> I try to recover it doing (from psql frontend):
>
> select field1 from table1 where field1 ~* 'ONE\\\'  ;

Heh.  This will probably work if you use *four* backslashes.  The
first time it gets parsed, 'ONE\\\\' -> 'ONE\\', because each '\\'
sequence will reduce to a single '\'.  Then the second time it gets
parsed, the '\\' -> '\', which is what you want.

(Haven't tested it, but I've seen similar things in other places.)

Chris

--
---------------------------------------------------- cjones@rightnowtech.com
Chris Jones
           System Administrator, Right Now Technologies, Inc.
"Is this going to be a stand-up programming session, sir, or another bug hunt?"