Calling script and passing value from called script - perl

I have one script i'm trying to call from another script, passing the information from the script that is being called to the calling script. When i use do or require it runs through but doesnt pass the value.
ex.
I have the following line at the bottom of the script that i am calling
called script.pl
print " $hold IS VALUE\n";
which prints me the value of hold.
I then start the calling script with:
calling_script.pl
require 'acc_option.pl';
print "HOLD PASSED IS $hold\n";
but the variable hold doesnt print.
Whats the best way to call this script instead of putting everything on one long ass page?

It depends on how $hold was declared.
If it was lexically declared (with "my $hold...") then you can't get at it directly - it's only accessible within the scope of called_script.pl.
If it's dynamically scoped (local $hold, or our $hold) then you should be able to get at it by prefixing it with the package it was declared under (so if it's in "package Foo;" you can get at it as $Foo::hold").
That said...
You generally don't want to mess around passing variables between scripts. Storing state in global variables can make for some nasty debugging sessions.
As a first step you might want to encapsulate accessing $hold inside a subroutine so in called_script.pl you have something like:
sub is_on_hold { return $hold };
which will return $hold when called (I'm assuming here that $hold is some kind of boolean state indicator. If it isn't name your subroutine in an appropriately intention revealing way :-)
If you describe how you're trying to use $hold in a bit more detail folk might be able to give some more specific advice on a better way of doing your task.

You have started down the right path, but are still a ways off. You should be using modules and the use statment, not code and the require statement. You should try reading perldoc perlmod and perldoc perlmodlib, but the general gist is:
decompose your process into functions
group those functions by what they do
put the groups of functions into modules
write a script that uses the modules and calls the functions
Think of the script as a skeleton and the functions as fleshing out the skeleton.
Here is a simple module and a script that uses it:
ExampleModule.pm:
package ExampleModule;
use strict;
use warnings;
use base 'Exporter';
our #EXPORT_OK = qw/do_first_thing do_second_thing do_third_thing/;
sub do_first_thing {
my ($thing) = #_;
return $thing + 1;
}
sub do_second_thing {
my ($thing) = #_;
return $thing + 1;
}
sub do_third_thing {
my ($thing) = #_;
return $thing + 1;
}
1;
example.pl:
#!/usr/bin/perl
use strict;
use warnings;
use ExampleModule qw/do_first_thing do_second_thing do_third_thing/;
my $thing = 0;
$thing = do_first_thing($thing);
$thing = do_second_thing($thing);
$thing = do_third_thing($thing);
print "$thing\n";

Related

Can variable declarations be placed in a common script

Before I start, the whole 'concept' may be technically impossible; hopefully someone will have more knowledge about such things, and advise me.
With Perl, you can "declare" global variables at the start of a script via my / our thus:
my ($a,$b,$c ..)
That's fine with a few unique variables. But I am using about 50 of them ... and the same names (not values) are used by five scripts. Rather than having to place huge my( ...) blocks at the start of each file, I'm wondering if there is a way to create them in one script. Note: Declare the namespace, not their values.
I have tried placing them all in a single file, with the shebang at the top, and a 1 at the bottom, and then tried "require", "use" and "do" to load them in. But - at certain times -the script complains it cannot find the global package name. (Maybe the "paths.pl" is setting up the global space relative to itself - which cannot be 'seen' by the other scripts)
Looking on Google, somebody suggested setting variables in the second file, and still setting the my in the calling script ... but that is defeating the object of what I'm trying to do, which is simply declare the name space once, and setting the values in another script
** So far, it seems if I go from a link in an HTML page to a perl script, the above method works. But when I call a script via XHTMLRequest using a similar setup, it cannot find the $a, $b, $c etc within the "paths" script
HTML
<form method="post" action="/cgi-bin/track/script1.pl>
<input type="submit" value="send"></form>
Perl: (script1.pl)
#shebang
require "./paths.pl"
$a=1;
$b="test";
print "content-type: text/html\n\n";
print "$a $b";
Paths.pl
our($a,
$b,
$c ...
)1;
Seems to work OK, with no errors. But ...
# Shebang
require "./paths.pl"
XHTMLREQUEST script1.pl
Now it complains it cannot find $a or $b etc as an "explicit package" for "script1.pl"
Am I moving into the territory of "modules" - of which I know little. Please bear in mind, I am NOT declaring values within the linked file, but rather setting up the 'global space' so that they can be used by all scripts which declare their own values.
(On a tangent, I thought - in the past - a file in the same directory could be accessed as "paths.pl" -but it won't accept that, and it insists on "./" Maybe this is part of the problem. I have tried absolute and relative paths too, from "url/cgi-bin/track/" to "/cgi-bin/track" but can't seem to get that to work either)
I'm fairly certain it's finding the paths file as I placed a "my value" before the require, and set a string within paths, and it was able to print it out.
First, lexical (my) variables only exist in their scope. A file is a scope, so they only exist in their file. You are now trying to work around that, and when you find yourself fighting the language that way, you should realize that you are doing it wrong.
You should move away from declaring all variables in one go at the top of a program. Declare them near the scope you want to use them, and declare them in the smallest scope possible.
You say that you want to "Set up a global space", so I think you might misunderstand something. If you want to declare a lexical variable in some scope, you just do it. You don't have to do anything else to make that possible.
Instead of this:
my( $foo, $bar, $baz );
$foo = 5;
sub do_it { $bar = 9; ... }
while( ... ) { $baz = 6; ... }
Declare the variable just where you want them:
my $foo = 5;
sub do_it { my $bar = 9; ... }
while( ... ) { my $baz = 6; ... }
Every lexical variable should exist in the smallest scope that can tolerate it. That way nothing else can mess with it and it doesn't retain values from previous operations when it shouldn't. That's the point of them, after all.
When you declare them to be file scoped, then don't declare them in the scope that uses them, you might have two unrelated uses of the same name conflicting with each other. One of the main benefits of lexical variables is that you don't have to know the names of any other variables in scope or in the program:
my( $foo, ... );
while( ... ) {
$foo = ...;
do_something();
...
}
sub do_something {
$foo = ...;
}
Are those uses of $foo in the while and the sub the same, or do they accidentally have the same name? That's a cruel question to leave up to the maintenance program.
If they are the same thing, make the subroutine get its value from its argument list instead. You can use the same names, but since each scope has it's own lexical variables, they don't interfere with each other:
while( ... ) {
my $foo = ...;
do_something($foo);
...
}
sub do_something {
my( $foo ) = #_;
}
See also:
How to share/export a global variable between two different perl scripts?
You say you aren't doing what I'm about to explain, but other people may want to do something similar to share values. Since you are sharing the same variable names across programs, I suspect that this is actually what it going on, though.
In that case, there are many modules on CPAN that can do that job. What you choose depends on what sort of stuff you are trying to share between programs. I have a chapter in Mastering Perl all about it.
You might be able to get away with something like this, where one module defines all the values and makes them available for export:
# in Local/Config.pm
package Local::Config;
use Exporter qw(import);
our #EXPORT = qw( $foo $bar );
our $foo = 'Some value';
our $bar = 'Different value';
1;
To use this, merely load it with use. It will automatically import the variables that you put in #EXPORT:
# in some program
use Local::Config;
We cover lots of this sort of stuff in Intermediate Perl.
What you want to do here is a form of boilerplate management. Shoving variable declarations into a module or class file. This is a laudable goal. In fact you should shove as much boilerplate into that other module as possible. It makes it far easier to keep consistent behavior across the many scripts in a project. However shoving variables in there will not be as easy as you think.
First of all, $a and $b are special variables reserved for use in sort blocks so they never have to be declared. So using them here will not validate your test. require always searches for the file in #INC. See perlfunc require.
To declare a variable it has to be done at compile time. our, my, and state all operate at compile time and legalize a symbol in a lexical scope. Since a module is a scope, and require and do both create a scope for that file, there is no way to have our (let alone my and state) reach back to a parent scope to declare a symbol.
This leaves you with two options. Export package globals back to the calling script or munge the script with a source filter. Both of these will give you heartburn. Remember that it has to be done at compile time.
In the interest of computer science, here's how you would do it (but don't do it).
#boilerplate.pm
use strict;
use vars qw/$foo $bar/;
1;
__END__
#script.pl
use strict;
use boilerplate;
$foo = "foo here";
use vars is how you declare package globals when strict is in effect. Package globals are unscoped ("global") so it doesn't matter what scope or file they're declared in. (NB: our does not create a global like my creates a lexical. our creates a lexical alias to a global, thus exposing whatever is there.) Notice that boilerplate.pm has no package declaration. It will inherit whatever called it which is what you want.
The second way using source filters is devious. You create a module that rewrites the source code of your script on the fly. See Filter::Simple and perlfilter for more information. This only works on real scripts, not perl -e ....
#boilerplate.pm
package boilerplate;
use strict; use diagnostics;
use Filter::Simple;
my $injection = '
our ($foo, $bar);
my ($baz);
';
FILTER { s/__FILTER__/$injection/; }
__END__
#script.pl
use strict; use diagnostics;
use boilerplate;
__FILTER__
$foo = "foo here";
You can make any number of filtering tokens or scenarios for code substitution. e.g. use boilerplate qw/D2_loadout/;
These are the only ways to do it with standard Perl. There are modules that let you meddle with calling scopes through various B modules but you're on your own there. Thanks for the question!
HTH

In Perl, how do I extract out the declaration of variables into a wrapper script?

Background
I have a perl script, called main.pl that is currently in several branched states on clear case like so:
Branch 1:
my %hash
my $variable = "a"
my $variable2 = "c"
sub codeIsOtherwiseTheSame()
....
Branch 2:
my %hash2
my $variable = "b"
sub codeIsOtherwiseTheSame()
....
Branch 3
my %hash
my $variable2 = "d"
sub codeIsOtherwiseTheSame()
....
Right now, each branch of the script has the same code. The only differences are the kind of variables that are declared and what their initialized value is. What I want to do is extract these differing variables out to a wrapper script (for each variation) so that the main script does not have to be changed. I am doing this because several users will be using this script, but have only minor differences based on their use case. Thus I want each kind of user to have their own simplified interface. At the same time, I want the main script to still be aware of these variable once it is called. Below is an example of what I want:
Desired Solution
Wrapper Script 1:
my %hash;
my $variable = "a";
my $variable2 = "c";
system("main.pl");
Wrapper Script 2:
my %hash2;
my $variable = "b";
system("main.pl");
Wrapper Script 3:
my %hash;
my $variable2 = "d";
system("main.pl");
Main.pl
sub codeIsOtherwiseTheSame()
Question
How do I extract out a wrapper script to obtain the organization and behavior I want above?
Extract the common code into a module, not a script. Save it as e.g. MyCommon.pm.
Export a function from the module that does what you need:
package MyCommon;
use Exporter qw{ import };
our #EXPORT = qw{ common_code };
sub common_code {
my ($var1, $var2) = #_;
# Common code goes here...
}
Then, in various scripts, write
use MyCommon qw{ common_code };
common_code('a', 'b'); # <- insert the specific values here.
There are more advanced ways, e.g. you can use "object orientation": construct an object from the specific values, then run a method that implements the common code - but for simple use cases, you probably don't need it.
Desired behavior for simple case as yours can be achieved with with required function of perl
Put common code in a file, for example common.inc end the file with 1; (requirement for modules and include files)
sub commonFunction {
my $data = shift;
print "DATA: $data\n";
}
1;
Copy/move common.inc file into one of #INC directory (probably site directory best fit for this purpose).
Check your perl #INC configuration setting with following command
perl -e "print qw(#INC)"
Now you can reuse common.inc file in your user interface script
#!/usr/bin/perl
require 'common.inc';
my $a = 7;
commonFunction($a);
Already was suggested to place the common code which will be reused multiple times in form of .pm module.
By doing so you gain more control what functions/variables are visible (exported) to avoid namespace clash/collision [the modules can have functions/variables with same name].
Short tutorial how to create a module is available. Next natural step will be OOP programming.
Book: Object Oriented Perl
perlootut, Writing perl modules, Chapter Object Oriented Perl

Call a subroutine defined as a variable

I am working on a program which uses different subroutines in separate files.
There are three parts
A text file with the name of the subroutine
A Perl program with the subroutine
The main program which extracts the name of the subroutine and launches it
The subroutine takes its data from a text file.
I need the user to choose the text file, the program then extracts the name of the subroutine.
The text file contains
cycle.name=cycle01
Here is the main program :
# !/usr/bin/perl -w
use strict;
use warnings;
use cycle01;
my $nb_cycle = 10;
# The user chooses a text file
print STDERR "\nfilename: ";
chomp($filename = <STDIN>);
# Extract the name of the cycle
open (my $fh, "<", "$filename.txt") or die "cannot open $filename";
while ( <$fh> ) {
if ( /cycle\.name/ ) {
(undef, $cycleToUse) = split /\s*=\s*/;
}
}
# I then try to launch the subroutine by passing variables.
# This fails because the subroutine is defined as a variable.
$cycleToUse($filename, $nb_cycle);
And here is the subroutine in another file
# !/usr/bin/perl
package cycle01;
use strict;
use warnings;
sub cycle01 {
# Get the total number of arguments passed
my ($filename, $nb_cycle) = #_;
print "$filename, $nb_cycle";
Your code doesn't compile, because in the final call, you have mistyped the name of $nb_cycle. It's helpful if you post code that actually runs :-)
Traditionally, Perl module names start with a capital letter, so you might want to rename your package to Cycle01.
The quick and dirty way to do this is to use the string version of eval. But evaluating an arbitrary string containing code is dangerous, so I'm not going to show you that. The best way is to use a dispatch table - basically a hash where the keys are valid subroutine names and the values are references to the subroutines themselves. The best place to add this is in the Cycle01.pm file:
our %subs = (
cycle01 => \&cycle01,
);
Then, the end of your program becomes:
if (exists $Cycle01::subs{$cycleToUse}) {
$Cycle01::subs{$cycleToUse}->($filename, $nb_cycle);
} else {
die "$cycleToUse is not a valid subroutine name";
}
(Note that you'll also need to chomp() the lines as you read them in your while loop.)
To build on Dave Cross' answer, I usually avoid the hash table, partly because, in perl, everything is a hash table anyway. Instead, I have all my entry-point subs start with a particular prefix, that prefix depends on what I'm doing, but here we'll just use ep_ for entry-point. And then I do something like this:
my $subname = 'ep_' . $cycleToUse;
if (my $func = Cycle01->can($subname))
{
$func->($filename, $nb_cycle);
}
else
{
die "$cycleToUse is not a valid subroutine name";
}
The can method in UNIVERSAL extracts the CODE reference for me from perl's hash tables, instead of me maintaining my own (and forgetting to update it). The prefix allows me to have other functions and methods in that same namespace that cannot be called by the user code directly, allowing me to still refactor code into common functions, etc.
If you want to have other namespaces as well, I would suggest having them all be in a single parent namespace, and potentially all prefixed the same way, and, ideally, don't allow :: or ' (single quote) in those names, so that you minimise the scope of what the user might call to only that which you're willing to test.
e.g.,
die "Invalid namespace $cycleNameSpaceToUse"
if $cycleNameSpaceToUse =~ /::|'/;
my $ns = 'UserCallable::' . $cycleNameSpaceToUse;
my $subname = 'ep_' . $cycleToUse;
if (my $func = $ns->can($subname))
# ... as before
There are definitely advantages to doing it the other way, such as being explicit about what you want to expose. The advantage here is in not having to maintain a separate list. I'm always horrible at doing that.

How to interpret a string as Perl code and execute it without eval

I understand that "string-eval" can be used for it. But I am looking for some alternative to achieve it without eval. Reason being "string-eval" fail the Perl critic and as per client policy I can not use it.
What are some alternative to do that without eval?
Here is what I am trying to do:
I am passing a dynamic generated code reference to a function. This function evaluates this code reference and assign the result to a variable.
Perl critic objects to string-eval because "interpreting a string as perl code and executing it" is generally a poor solution to any problem.
You can't work around it by just finding another function to do the same thing (well, you could, but that would be entirely missing the point).
Coderefs do not need eval to run. Simply dereference a coderef to invoke it. This is explained in perldoc perlref.
my $code = sub {
my ($name) = #_;
say "Hi, $name!";
};
$code->('rpg');
This works for me.
#!/usr/bin/perl
use strict;
use warnings;
sub exec_code {
my ($c) = #_;
return &{$c};
}
my $coderef = sub {
print "Hello, from sub";
};
exec_code($coderef);

imported perl variable imports with no value

SOLVED: As it turns out, my problem was rooted in the fact that I was not putting a $ in front of DEBUGVAR in the #EXPORT_OK assignment and the "use config_global qw(config DEBUGVAR);" line. Since it raises no error, I had no way to know this was the issue. So, the fix is to place the proper syntax in front of your variables at these points.
So I am trying to get the hang of writing and importing perl modules. I don't know why it was made so difficult to do this, but I am having a great deal of trouble with this seeimingly trivial task. Here is the contents of my module:
package global_config;
use strict;
require Exporter;
our #ISA = qw(Exporter);
our #EXPORT_OK = qw(DEBUGVAR);
our ($DEBUGVAR);
our $DEBUGVAR = "Hello, World!";
return 1;
Here are the contents of my perl script that imports the module:
use strict;
use config_global qw(config, DEBUGVAR);
our %config;
our $DEBUGVAR;
print "variable imported with value: ".$DEBUGVAR;
The output is "variable imported with value:", and nothing else. My variable appears to be losing it's value. What am I doing wrong?
EDIT: After fiddling around a bit, and turning warnings on, I have isolated the issue to being that $DEBUGVAR is never actually imported. When I use it via $config_global:DEBUGVAR, it works as expected. The issue now is that it is not importing into the namespace. What gives?
I see several issues:
You should not use a comma in the qw() syntax. The qw takes each whitespace separated phrase and puts it in an array element.
These two are the same:
my #bar = qw(foo bar barfu); #No commas!
my #bar = ("foo", "bar", "barfu"); #Commas Required
If you're exporting a variable, you need to put the sigil in front of it.
You have:
our #EXPORT_OK = qw(DEBUGVAR);
It should be:
our #EXPORT_OK = qw($DEBUGVAR);
You should use the newer Exporter syntax:
Here's the newer Exporter Syntax:
package global_config;
use strict;
use warnings;
use Exporter 'import'; #Not "require". No need for "#ISA"
our #EXPORT_OK = qw(DEBUGVAR);
our $DEBUGVAR = "Hello, World";
1; #Makes no real difference, but you shouldn't say "return 1". Just standard.
Finally, what are you doing exporting variables? That's just a bad practice.
Exporting anything is now questioned -- even functions. It pollutes the user's namespace. (At least you're using #EXPORT_OKAY). Take a look at File::Spec. It uses fully qualified package names for its subroutines by default.
The variable in question is accessible via the full package name $global_config::DEBUGVAR, so there's no real need to export it.
What if everybody did it? Yes, you last heard of this excuse in kindergarten, but it applies here. Imagine if several modules exported $DEBUGVAR.
There are several ways around your quandary, but the best is to use object oriented Perl to help set this variable, and even allow users to change it.
package MyPackage;
use strict;
use warnings;
use feature qw(say);
sub new {
my $class = shift;
my $debug = shift; #Optional Debug Value
my $self = {};
bless $self, $class;
if (not defined $debug) {
$debug = "Hello, world!";
$self->Debug($debug);
return $self;
}
sub Debug {
my $self = shift;
my $debug = shift;
if (defined $debug) {
$self->{DEBUG} = $debug;
}
return $debug;
}
1;
To use this module, I simply create a new object, and Debug will be set for me:
use strict;
use warnings;
use MyPackage #No exporting needed
#Create an object w/ Debug value;
my $obj = MyPackage->new; #Debug is the default.
say $obj->Debug; #Prints "Hello, world!"
# Change the value of Debug
$obj->Debug("Foo!");
say $obj->Debug; #Now prints "Foo!"
#Create a new object with a different default debug
$obj2 = MyPackage->new("Bar!");
say $obj2->Debug; #Print "Bar!";
This solves several issues:
It allows multiple values of debug because each object now has its own values
There is no worry about namespace pollution or accessing package variables. Again, all you need is contained in the object itself.
It's easier to debug issues since the complexity is hidden inside the objects themselves.
It's the new preferred method, so you might as well get use to the syntax and be able to read object oriented Perl code. You'll be seeing it more and more.
While exporting variables from a package isn't necessarily a recommended practice, to do so, you need to use the actual name of the variable you are exporting. In this case it is $DEBUGVAR and not DEBUGVAR which would be the name of a subroutine.
In the script using the config module, you do not need to declare the $DEBUGVAR variable as our, since imported variables are exempt from strict vars.
You have gotten the name mixed up, it looks like:
use config_global ...
package global_config;
Though one would think that would issue warnings. Unless you are not using warnings...?
ETA:
our #EXPORT_OK = qw($DEBUGVAR);
^
Also, you have two declarations on that variable. You really need to use warnings when debugging, otherwise, you'll never get anywhere.
Are you sure you want a comma here:
use config_global qw(config, DEBUGVAR);
Also, you aren't exporting config, so it might work better as:
use config_global qw(DEBUGVAR);
I'd also remove the last our $DEBUGVAR; since it might set it to undef (or at least put it before the "use" line) -- I am not sure about this though.