Escaping Backslashes in Postgresql - postgresql

Question

I need to write a file to disk from postgres that has character string of a backslash immediately followed by a forward slash \/
Code similar to this has not worked:
drop table if exists test;
create temporary table test (linetext text);
insert into test values ('\/\/foo foo foo\/bar\/bar');
copy (select linetext from test) to '/filepath/postproductionscript.sh';
The above code yields \\/\\/foo foo foo\\/bar\\/bar ... it inserts an extra backslash.
When you view the temp table, the string is correctly viewed as \/\/, so I am not sure where or when the text is changed into \\/\\/
I've tried doubling the \, variations of E before the string, and quote_literal() without luck.
I have note found a solution here Postgres Manual
Running Postgres 9.2, encoded UTF-8.

Answer 1

The problem is that COPY is not intended to write out plain-text files. It is intended to write out files that can be read back by COPY. And the semi-internal encoding that it uses does some backslash escaping.
For what you want to do, you need to write some custom code. Either use a normal client library to read the query results and write them to a file, or, if you want to do it in-server, use something like PL/Perl or PL/Python.

Answer 2

The \ excaping is only recognised if the stringliteral is prefixed with E , otherwise the standard_conforming_strings setting (or the like) is respected (ANSI-SQL has a different way of string escaping, probably stemming from COBOL;-).
drop table if exists test;
create temporary table test (linetext text);
insert into test values ( E'\/\/foo foo foo\/bar\/bar');
copy (select linetext from test) to '/tmp/postproductionscript.sh';
UPATE: an ugly hack is to use .csv format and still use \t as delimter.
The #!/bin/sh as a shebang headerline should be consdered a feature
-- without a header line
drop table if exists test;
create temporary table test (linetext text);
insert into test values ( '\/\/foo foo foo\/bar\/bar');
copy (select linetext AS "#linetext" from test) to '/tmp/postproductionscript_c.sh'
WITH CSV
DELIMITER E'\t'
;
-- with a shebang header line
drop table if exists test;
create temporary table test (linetext text);
insert into test values ( '\/\/foo foo foo\/bar\/bar');
copy (select linetext AS "#/bin/sh" from test) to '/tmp/postproductionscript_h.sh'
WITH CSV
HEADER
DELIMITER E'\t'
;