-
-
PL/perl - Perl Procedural Language
+
+
PL/Perl - Perl Procedural Language
+
+ PL/Perl allows you to write functions in the Perl programming
+ language which may be used in SQL queries as if they were built into
+
+
+ The PL/Perl intepreter is a full Perl interpreter. However, certain
+ operations have been disabled in order to maintain the security of
+ the system. In general, the operations that are restricted are
+ those that interact with the environment. This includes filehandle
+ operations, require, and use
+ (for external modules). It should be noted that this security is
+ not absolute. Indeed, several Denial-of-Service attacks are still
+ possible - memory exhaustion and endless loops are two examples.
+
+
+
+
Building and Installing
- This chapter describes how to compile, install and
- use PL/Perl.
+ In order to build and install PL/Perl if you are installing
+
Postgres from source then the
+ must be supplied to the
+ configure script. PL/Perl requires that, when
+
Perl was installed, the
+ libperl library was build as a shared object.
+ At the time of this writing, this is almost never the case in the
+ Perl packages that are distributed with the operating systems. A
+ message like this will appear during the build to point out this
+ fact:
+
+
+*****
+* Cannot build PL/Perl because libperl is not a shared library.
+* Skipped.
+*****
+
+
+ Therefore it is likely that you will have to re-build and install
+
Perl manually to be able to build
+ PL/Perl.
-
-
Overview
- PL/Perl allows you to write functions in the Perl scripting
- language which may be used in SQL queries as if they were
-
- The PL/Perl intepreter is a full Perl interpreter. However,
- certain operations have been disabled in order to increase
- the security level of the system.
-
- In general, the operations that are restricted are those that
- interact with the environment. This includes filehandle operations,
- require, and use (for external
- modules).
-
- It should be noted that this security is not absolute. Indeed, several
- Denial-of-Service attacks are still possible - memory exhaustion and
- endless loops are two.
-
-
-
-
Building and Installing
- Assuming that the
Postgres- source tree is rooted at $PGSRC, then the Pl/perl source
- code is located in $PGSRC/src/pl/plperl.
-
- To build, simply do the following:
-cd $PGSRC/src/pl/plperl
-perl Makefile.PL
-make
-
-
+ When you want to retry to build PL/Perl after having reinstalled
+ Perl, then change to the directory
+ src/pl/plperl in the
+
Postgres source tree and issue the commands
+gmake clean
+gmake all
+gmake install
+
+
- This will create a shared library file. On a Linux system, it will be
- named plperl.so. The extension may differ on other systems.
-
- The shared library should then be copied into the lib subdirectory of the
- postgres installation.
-
- The createlang command is used to install the language into a database.
- If it is installed into template1, all future databases will have the
- language installed automatically.
-
-
+ The createlang command is used to install the
+ language into a database.
+
+
$ createlang plperl template1+
+ If it is installed into template1, all future databases will have
+ the language installed automatically.
+
+
-
-
Using PL/Perl
- Assume you have the following table:
+
+
Using PL/Perl
+
+ Assume you have the following table:
CREATE TABLE EMPLOYEE (
name text,
- basesalary int4,
- bonus int4 );
-
-
- In order to get the total compensation (base + bonus) we could
- define a function as follows:
-CREATE FUNCTION totalcomp(int4, int4) RETURNS int4
+ basesalary integer,
+ bonus integer
+);
+
+
+ In order to get the total compensation (base + bonus) we could
+ define a function as follows:
+CREATE FUNCTION totalcomp(integer, integer) RETURNS integer
AS 'return $_[0] + $_[1]'
LANGUAGE 'plperl';
-
+
- Note that the arguments are passed to the function in
- @_ as might be expected. Also, because
- of the quoting rules for the SQL creating the function, you
- may find yourself using the extended quoting functions (qq[],
- q[], qw[]) more often that you are used to.
-
- We may now use our function like so:
-SELECT name, totalcomp(basesalary, bonus) from employee
-
-
- But, we can also pass entire tuples to our function:
-CREATE FUNCTION empcomp(employee) returns int4
- AS 'my $emp = shift;
- return $emp->{''basesalary''} + $emp->{''bonus''};'
- LANGUAGE 'plperl';
-
- A tuple is passed as a reference to hash. The keys are the names of
- fields in the tuples. The values are values of the corresponding
- field in the tuple.
-
+ Notice that the arguments to the function are passed in
+ @_ as might be expected.
+
+
+ We can now use our function like so:
+SELECT name, totalcomp(basesalary, bonus) FROM employee;
+
+
+
+ But, we can also pass entire tuples to our functions:
+CREATE FUNCTION empcomp(employee) RETURNS integer AS '
+ my $emp = shift;
+ return $emp->{''basesalary''} + $emp->{''bonus''};
+' LANGUAGE 'plperl';
+
+ A tuple is passed as a reference to a hash. The keys are the names
+ of the fields in the tuples. The hash values are values of the
+ corresponding fields in the tuple.
+
+
+
- The new function empcomp can used like:
-SELECT name, empcomp(employee) from employee;
-
+ Because the function body is passed as an SQL string literal to
+ CREATE FUNCTION you have to escape single
+ quotes within your Perl source, either by doubling them as shown
+ above, or by using the extended quoting functions
+ (q[], qq[],
+ qw[]). Backslashes must be escaped by doubling
+ them.
-
-
+
+
+ The new function empcomp can used like:
+SELECT name, empcomp(employee) FROM employee;
+
+
+
+ Here is an example of a function which will not work because file
+ system operations are not allowed for security reasons:
+CREATE FUNCTION badfunc() RETURNS integer AS '
+ open(TEMP, ">/tmp/badfile");
+ print TEMP "Gotcha!\n";
+ return 1;
+' LANGUAGE 'plperl';
+
+ The creation of the function will succeed, but executing it will not.
+
+
+
+
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