Re: Unfamiliar syntax
From: James Kerwin
Afternoon all,
I have been asked to take a look at a .pl file which is part of a set-up
called "EPrints". The particular file controls who can access documents on a
server.
Excluding some comments, the file starts like:
$c->{can_request_view_document} = sub
{
my( $doc, $r ) = @_;
It then goes on to complete the subroutine and return a value.
I understand that $doc and $r are populated via @_ but I have never before
seen the structure of the first line starting with "$c". Additionally, the file
doesn't look like a typical Perl file (eg.#!/usr/bin/perl -w at the top and
some use statements).
I know it's very vague, but could anybody explain this syntax to me? My
suspicion is that something else is calling the subroutines in this file? Am I
at least on the right track?
Thanks,
James
Hi, James
Yes, you are on the right track.
This is an annonymous subroutine which is probably used as a callback
subroutine somewhere else.
You can define such subroutines using a code like:
my $my_sub = sub { ... }
Then you can use the $my_sub variable as any other scalar variables, for
example as a parameter in another subroutine call, like:
do_something( $my_sub );
...then the sub do_something could use this sub like:
sub do_something {
my ( $sub ) = @_;
$sub->(); #execute the callback subroutine here
}
If this subroutine accepts parameters, you can call it like:
$my_sub->( $doc, $r );
Now, in your case, you don't have a scalar variable $my_sub to store this
subroutine, but you have another scalar value of a hashref $c, stored in the
key can_request_view_document, which is $c->{can_request_view_document},.
So in order to execute this sub, you do:
$c->{can_request_view_document}->( $doc, $r );
The code is common Perl code. It doesn't matter that the file doesn't start
with #!/usr/bin/perl
The shebang line is not needed if the program is executed with a command like:
perl program.pl
--Octavian
Re: Unfamiliar syntax
I Found it on github
https://github.com/eprints/eprints/blob/392474eec1b8125a66ed2d3e12b02aeb67dc07c4/lib/defaultcfg/cfg.d/security.pl
On 7/20/18 6:24 PM, Chas. Owens wrote:
All of this is supposition since I can't see anything you haven't
shown us.
It sounds like this code is part of a larger program that is going to
call
do "EPrints";
which will bring the source of EPrints into the larger program. The $c
variable is probably setup there. What the code in EPrints is doing
is setting up a handler named can_request_view_document. At some
point in the larger program, it is going to say something like
my $document = $r->param(doc);
my $can_request = $c->{can_request_view_document}->($document, $r);
return 403, "You are not allowed to access $document" unless $can_request;
return 400, "$document doesn't exist" unless -f $document;
return 200, $document;
On Fri, Jul 20, 2018 at 11:06 AM James Kerwin > wrote:
Afternoon all,
I have been asked to take a look at a .pl file which is part of a
set-up called "EPrints". The particular file controls who can
access documents on a server.
Excluding some comments, the file starts like:
$c->{can_request_view_document} = sub
{
my( $doc, $r ) = @_;
It then goes on to complete the subroutine and return a value.
I understand that $doc and $r are populated via @_ but I have
never before seen the structure of the first line starting with
"$c". Additionally, the file doesn't look like a typical Perl file
(eg.#!/usr/bin/perl -w at the top and some use statements).
I know it's very vague, but could anybody explain this syntax to
me? My suspicion is that something else is calling the subroutines
in this file? Am I at least on the right track?
Thanks,
James
Re: Unfamiliar syntax
Hi!
$c is hash reference with key "can_request_view_document";
The value for that key is anonymous sub.
You can call this sub like this
$c->{can_request_view_document}->($doc, $r);
On 7/20/18 6:04 PM, James Kerwin wrote:
Afternoon all,
I have been asked to take a look at a .pl file which is part of a
set-up called "EPrints". The particular file controls who can access
documents on a server.
Excluding some comments, the file starts like:
$c->{can_request_view_document} = sub
{
my( $doc, $r ) = @_;
It then goes on to complete the subroutine and return a value.
I understand that $doc and $r are populated via @_ but I have never
before seen the structure of the first line starting with "$c".
Additionally, the file doesn't look like a typical Perl file
(eg.#!/usr/bin/perl -w at the top and some use statements).
I know it's very vague, but could anybody explain this syntax to me?
My suspicion is that something else is calling the subroutines in this
file? Am I at least on the right track?
Thanks,
James
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Re: Unfamiliar syntax
All of this is supposition since I can't see anything you haven't shown us.
It sounds like this code is part of a larger program that is going to call
do "EPrints";
which will bring the source of EPrints into the larger program. The $c
variable is probably setup there. What the code in EPrints is doing is
setting up a handler named can_request_view_document. At some point in the
larger program, it is going to say something like
my $document = $r->param(doc);
my $can_request = $c->{can_request_view_document}->($document, $r);
return 403, "You are not allowed to access $document" unless $can_request;
return 400, "$document doesn't exist" unless -f $document;
return 200, $document;
On Fri, Jul 20, 2018 at 11:06 AM James Kerwin wrote:
> Afternoon all,
>
> I have been asked to take a look at a .pl file which is part of a set-up
> called "EPrints". The particular file controls who can access documents on
> a server.
>
> Excluding some comments, the file starts like:
>
> $c->{can_request_view_document} = sub
> {
> my( $doc, $r ) = @_;
>
> It then goes on to complete the subroutine and return a value.
>
> I understand that $doc and $r are populated via @_ but I have never before
> seen the structure of the first line starting with "$c". Additionally, the
> file doesn't look like a typical Perl file (eg.#!/usr/bin/perl -w at the
> top and some use statements).
>
> I know it's very vague, but could anybody explain this syntax to me? My
> suspicion is that something else is calling the subroutines in this file?
> Am I at least on the right track?
>
> Thanks,
> James
>
Re: Unfamiliar syntax
2018-07-20 16:04:11 +0100 James Kerwin:
> Afternoon all,
>
> I have been asked to take a look at a .pl file which is part of a set-up
> called "EPrints". The particular file controls who can access documents on
> a server.
>
> Excluding some comments, the file starts like:
>
> $c->{can_request_view_document} = sub
> {
> my( $doc, $r ) = @_;
>
> It then goes on to complete the subroutine and return a value.
>
> I understand that $doc and $r are populated via @_ but I have never before
> seen the structure of the first line starting with "$c". Additionally, the
> file doesn't look like a typical Perl file (eg.#!/usr/bin/perl -w at the
> top and some use statements).
Maybe some piece of code is doing "do 'the_file.pl'" or the file's
content is being given to eval(). In these cases, probably a hashref
$c was already declared and being used in the code that runs the do()
or eval().
> I know it's very vague, but could anybody explain this syntax to me? My
> suspicion is that something else is calling the subroutines in this file?
> Am I at least on the right track?
>
> Thanks,
> James
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Unfamiliar syntax
Afternoon all,
I have been asked to take a look at a .pl file which is part of a set-up
called "EPrints". The particular file controls who can access documents on
a server.
Excluding some comments, the file starts like:
$c->{can_request_view_document} = sub
{
my( $doc, $r ) = @_;
It then goes on to complete the subroutine and return a value.
I understand that $doc and $r are populated via @_ but I have never before
seen the structure of the first line starting with "$c". Additionally, the
file doesn't look like a typical Perl file (eg.#!/usr/bin/perl -w at the
top and some use statements).
I know it's very vague, but could anybody explain this syntax to me? My
suspicion is that something else is calling the subroutines in this file?
Am I at least on the right track?
Thanks,
James
