In what order does a program run..??

[Richard C 1]

I'm new to PERL and am trying to learn by reading some PERL programs.

My question is this - does PERL execute sequentially and "skip around"
embedded subroutines or
Does it execute them inline?

For example, if the program has the following set of code lines

Line1
Line2
Line3
Sub1
Subcode1
Subcode2
Endsub1
Line4
Line5
Line6 calls sub1
Line7


Does the execution sequence go like this:

Line1, line2, line3 line 4 line5, line6, sub1, subcode1, subcode2,
endsub1 line7

Or does it go like this:

Line1, Line2, Line3, Sub1, Subcode1, Subcode2, Endsub1, Line4, Line5,
Line6, Sub1, Subcode1, Subcode2, Endsub1, Line7

Thanks.

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[Jeff 'Japhy' Pinyan]

On Feb 4, [email]Richard.C.1@bwc.state.oh.us[/email] said:

>My question is this - does PERL execute sequentially and "skip around"
>embedded subroutines or Does it execute them inline?

Perl *compiles* subroutines when it sees them, but does NOT run them
UNLESS you call them.

>Line1
>Line2
>Line3
>Sub1
>Subcode1
>Subcode2
>Endsub1
>Line4
>Line5
>Line6 calls sub1
>Line7

>Does the execution sequence go like this:
>
>Line1, line2, line3 line 4 line5, line6, sub1, subcode1, subcode2,
>endsub1 line7

Yes.

--
Jeff "japhy" Pinyan [email]japhy@pobox.com[/email] [url]http://www.pobox.com/~japhy/[/url]
RPI Acacia brother #734 [url]http://www.perlmonks.org/[/url] [url]http://www.cpan.org/[/url]
<stu> what does y/// stand for? <tenderpuss> why, yansliterate of course.
[ I'm looking for programming work. If you like my work, let me know. ]

[Wiggins D Anconia]

>

>
> I'm new to PERL and am trying to learn by reading some PERL programs.
>

Perl or perl, never PERL. perldoc -q '"Perl"'

Sometimes that is good, sometimes bad depending on who wrote the Perl
you are reading, it is one way to pick up very bad habits. Does the
code you are reading have:

use strict;
use warnings;

At the top? If not you may be better off walking away slowly and then
checking out a book (see suggestion below) or one of the free online
resources first, then come back to the code. [url]http://learn.perl.org[/url]

> My question is this - does PERL execute sequentially and "skip around"
> embedded subroutines or
> Does it execute them inline?

It skips them as they are definitions....

>
> For example, if the program has the following set of code lines
>
> Line1
> Line2
> Line3
> Sub1
> Subcode1
> Subcode2
> Endsub1
> Line4
> Line5
> Line6 calls sub1
> Line7
>
>
> Does the execution sequence go like this:
>
> Line1, line2, line3 line 4 line5, line6, sub1, subcode1, subcode2,
> endsub1 line7
>

Correct (if I am understanding your 'sub1' correctly).

> Or does it go like this:
>
> Line1, Line2, Line3, Sub1, Subcode1, Subcode2, Endsub1, Line4, Line5,
> Line6, Sub1, Subcode1, Subcode2, Endsub1, Line7
>
> Thanks.
>

You may want to look at,

perldoc perl

and review some of the basics. An excellent resource is also Learning
Perl from O'Reilly and will get you all of the basics you will need and
give you familarity with how to do things in a Perlish way.

Good luck and welcome,

[url]http://danconia.org[/url]

[James Edward Gray II]

On Feb 4, 2004, at 9:52 AM, <Richard.C.1@bwc.state.oh.us> wrote:

> I'm new to PERL and am trying to learn by reading some PERL programs.

Welcome then. Look's like you already got your answer, but here's a
tip: "perl" refers to the program that compiles and runs programs
written in the "Perl" programming language, but we don't know what
"PERL" is. ;)

James

[Rob Dixon]

Wiggins D Anconia wrote:

> >
> >
> > I'm new to PERL and am trying to learn by reading some PERL programs.
> >

>
> Perl or perl, never PERL. perldoc -q '"Perl"'

Only on Unix:

perldoc "What's the difference"

will work.

Rob

[James Edward Gray II]

On Feb 4, 2004, at 12:11 PM, Rob Dixon wrote:

> Wiggins D Anconia wrote:

>>>
>>>
>>> I'm new to PERL and am trying to learn by reading some PERL programs.
>>>

>>
>> Perl or perl, never PERL. perldoc -q '"Perl"'

>
> Only on Unix:
>
> perldoc "What's the difference"

I believe you missed a -q in there:

perldoc -q "What's the difference"

James

[Randy W. Sims]

On 2/4/2004 10:52 AM, [email]Richard.C.1@bwc.state.oh.us[/email] wrote:

> I'm new to PERL and am trying to learn by reading some PERL programs.
>
> My question is this - does PERL execute sequentially and "skip around"
> embedded subroutines or
> Does it execute them inline?

In depth answer:

perl reads in your source file and parses the code from top to bottom.
If it sees a 'use <module>;' statement it stops parsing your file, reads
and parses the used module, and then resumes parsing your source. If it
encounters any 'BEGIN' subs (there can be more than one), it executes
the code in that sub as soon as the complete sub has been completely
parsed, but before parsing the remainder of your source. After the
source has been parsed, perl executes any 'CHECK' subs (there can be
more than one) beginning with the last, continuing in the *reverse*
order of definition. If you specify the '-c' (compile-only) switch, the
process ends here. Otherwise perl continues execution at the top first
with the execution of any 'INIT' subs in the order they are defined.
Then perl begins executing any code at file scope, executing code in
subroutines only when (or if) they are called. Afterwards, perl executes
any 'END' subs in reverse order of definition.

Randy.

[R. Joseph Newton]

[email]Richard.C.1@bwc.state.oh.us[/email] wrote:

> I'm new to PERL and am trying to learn by reading some PERL programs.
>
> My question is this - does PERL execute sequentially and "skip around"
> embedded subroutines or
> Does it execute them inline?
>
> For example, if the program has the following set of code lines

It is helpful to stop here and recheck your concept of code structure. Lines are meaningful only as debugging indexes in Perl. *There are not units of code*. Commands are delimited by semi-colons, and blocks by braces.

>
> Line1
> Line2
> Line3
> Sub1
> Subcode1
> Subcode2
> Endsub1
> Line4
> Line5
> Line6 calls sub1
> Line7
>
> Does the execution sequence go like this:
>
> Line1, line2, line3 line 4 line5, line6, sub1, subcode1, subcode2,
> endsub1 line7
>
> Or does it go like this:
>
> Line1, Line2, Line3, Sub1, Subcode1, Subcode2, Endsub1, Line4, Line5,
> Line6, Sub1, Subcode1, Subcode2, Endsub1, Line7
>

Generally, I would expect it to go kablooie. The intersperding of random lines of global script among subroutine definitions indicates poor program design. Although I often will write long sequences in global namespace when working out a problem, just to stay focused on the overall problem, I would not want to leave
working code in that condition

Generally, I seek to have the entire scripting content of a program covered in the first ten or twenty lines, and have everything beyond that properly encapsulaed in subroutine definitions. You gain much more control of progam execution by doing this, and can prevent and detect bugs much more easily.

The overall structure of a program should be much more like

#!shebang/path

use strict;
use warnings;

use Other;

whole_process(@ARGV);

script lines

sub whole_process {
first_major_subprocess();
next_major_subprocess();
....
}

sub first_major_subprocess{
useful_helper_process();
another_utility_process();
}

sub useful_helper_process {
}
...

Joseph