Thread: dollar-quoting in psql and in general
While trying to understand dollar-quoting, I found the following in psql: select $a$ hello $a$; behaves as expected, but psql does not like select $a$ \ $a$; or select $a$ \\ $a$; Should it? How should a dollar-quote handle: $a$ \$a\$a $a$ ? ---------------------------------------------------------------- Philip Warner | __---_____ Albatross Consulting Pty. Ltd. |----/ - \ (A.B.N. 75 008 659 498) | /(@) ______---_ Tel: (+61) 0500 83 82 81 | _________ \ Fax: (+61) 03 5330 3172 | ___________ | Http://www.rhyme.com.au | / \| | --________-- PGP key available upon request, | / and from pgp.mit.edu:11371 |/
Philip Warner <pjw@rhyme.com.au> writes:
> While trying to understand dollar-quoting, I found the following in psql:
> select $a$ hello $a$;
> behaves as expected, but psql does not like
> select $a$ \ $a$;
> or
> select $a$ \\ $a$;
Define "does not like". The behavior seems correct to me.
> Should it? How should a dollar-quote handle:
> $a$ \$a\$a $a$
The value of that is " \$a\$a ". Backslashes are not special inside
dollar quotes --- nor is anything else, except the matching close tag.
regards, tom lane
At 12:47 PM 12/08/2004, Tom Lane wrote: >Backslashes are not special inside >dollar quotes --- nor is anything else, except the matching close tag If they are not special, then shouldnt: select $a$\$a$; result in ?column? \ rather than an error? ---------------------------------------------------------------- Philip Warner | __---_____ Albatross Consulting Pty. Ltd. |----/ - \ (A.B.N. 75 008 659 498) | /(@) ______---_ Tel: (+61) 0500 83 82 81 | _________ \ Fax: (+61) 03 5330 3172 | ___________ | Http://www.rhyme.com.au | / \| | --________-- PGP key available upon request, | / and from pgp.mit.edu:11371 |/
>At 12:47 PM 12/08/2004, Tom Lane wrote: >>Backslashes are not special inside >>dollar quotes --- nor is anything else, except the matching close tag > >If they are not special, then shouldnt: > > select $a$\$a$; > >result in > > ?column? > \ > >rather than an error? Oops. It does. ---------------------------------------------------------------- Philip Warner | __---_____ Albatross Consulting Pty. Ltd. |----/ - \ (A.B.N. 75 008 659 498) | /(@) ______---_ Tel: (+61) 0500 83 82 81 | _________ \ Fax: (+61) 03 5330 3172 | ___________ | Http://www.rhyme.com.au | / \| | --________-- PGP key available upon request, | / and from pgp.mit.edu:11371 |/
Philip Warner wrote: > While trying to understand dollar-quoting, I found the following in psql: > > select $a$ hello $a$; > > behaves as expected, but psql does not like > > select $a$ \ $a$; > or > select $a$ \\ $a$; > > Should it? How should a dollar-quote handle: > > $a$ \$a\$a $a$ > > ? > > andrew=# select $a$ \ $a$;?column? ---------- \ (1 row) andrew=# select $a$ \\ $a$;?column? ---------- \\ (1 row) It is behaving as *I* expect, and as designed. \ is not magical inside dollar quotes, and if it were it would defeat the whole purpose of having them. Dollar quotes are really designed for strings that are reparsed - most typically function bodies. The strings inside them are therefore totally opaque, and there is no escape character. Otherwise, if we wanted the plpgsql parsers, say, to see \ we'd have to write \\, and the idea was to get away from \\, \', '' and friends. cheers andrew
At 01:07 PM 12/08/2004, Andrew Dunstan wrote: >\ is not magical inside dollar quotes, Sorry, I was confused by the manual: the paragraph that starts "C-style backslash escapes are also available..." is right after the paragraphs on dollar-quoting. The section on dollar-quoting is also not explicit about valid tags, "zero or more characters" is all I can see. Can you give me a definitive answer as to what is valid? AFAICT, must be [A-Z,a-z,0-9,_]*, with non-numeric start. Is that right? ---------------------------------------------------------------- Philip Warner | __---_____ Albatross Consulting Pty. Ltd. |----/ - \ (A.B.N. 75 008 659 498) | /(@) ______---_ Tel: (+61) 0500 83 82 81 | _________ \ Fax: (+61) 03 5330 3172 | ___________ | Http://www.rhyme.com.au | / \| | --________-- PGP key available upon request, | / and from pgp.mit.edu:11371 |/
Philip Warner <pjw@rhyme.com.au> writes:
> At 12:47 PM 12/08/2004, Tom Lane wrote:
>> Backslashes are not special inside
>> dollar quotes --- nor is anything else, except the matching close tag
> If they are not special, then shouldnt:
> select $a$\$a$;
> result in
> ?column?
> \
> rather than an error?
Worksforme (TM).
regression=# select $a$\$a$;?column?
----------\
(1 row)
regression=#
Are you sure your psql and backend are both current?
regards, tom lane
Philip Warner <pjw@rhyme.com.au> writes:
> At 01:07 PM 12/08/2004, Andrew Dunstan wrote:
>> \ is not magical inside dollar quotes,
> Sorry, I was confused by the manual: the paragraph that starts "C-style
> backslash escapes are also available..." is right after the paragraphs on
> dollar-quoting.
The documentation for dollar-quoting is pretty awful at the moment, as
it seems to have been pasted in with no thought to context, and is
incomplete anyway. I have on my to-do list to go over it, but if
someone else beats me to it I won't pout.
> The section on dollar-quoting is also not explicit about valid tags, "zero
> or more characters" is all I can see.
Use the source, Luke ... scan.l explains
/* $foo$ style quotes ("dollar quoting")* The quoted string starts with $foo$ where "foo" is an optional string* in the
formof an identifier, except that it may not contain "$", * and extends to the first occurrence of an identical string.
* There is *no* processing of the quoted text.*/
dolq_start [A-Za-z\200-\377_]
dolq_cont [A-Za-z\200-\377_0-9]
dolqdelim \$({dolq_start}{dolq_cont}*)?\$
regards, tom lane
Philip Warner wrote:
> At 01:07 PM 12/08/2004, Andrew Dunstan wrote:
>
>> \ is not magical inside dollar quotes,
>
>
> Sorry, I was confused by the manual: the paragraph that starts
> "C-style backslash escapes are also available..." is right after the
> paragraphs on dollar-quoting.
>
> The section on dollar-quoting is also not explicit about valid tags,
> "zero or more characters" is all I can see. Can you give me a
> definitive answer as to what is valid? AFAICT, must be
> [A-Z,a-z,0-9,_]*, with non-numeric start. Is that right?
>
>
Don't forget the high-bit chars too. pgsqlscan.l says:
dolq_start [A-Za-z\200-\377_]
dolq_cont [A-Za-z\200-\377_0-9]
dolqdelim \$({dolq_start}{dolq_cont}*)?\$
The scanner files for plpgsql and the backend have equivalent specs, so
this is definitive.
cheers
andrew