«

Good evening everyone.

I am currently in college doing a National Diploma in computing. Most of the
guys there haven't studied HTML or CSS or the likes and next year I think
they may be asking us to do ASP. I'm not very fond of the idea at all, so I
thought I would code my first assignment in Perl.

I had to work with 2 friends however and they have never seen perl, or even
heard of it. In fact, the looks on peoples faces when I did a presentation
on Larry Wall and Perl were kind of strange to say the least.

Anyway, to the point. I am quite new to perl myself, but I absolutely adore
it already. I am very keen to learn and make good habits from the very
beginning. I hope you don't mind, but here is a program I have made in Perl
to convert HTML files into CGI. I will use this while working with my
friends.

I would love to accept any criticism's. It is one of my first programs, but
don't miss anything. One thing I hate is getting into bad habits, so I would
like to pick them up now.

Anyway, here goes.
Thanks alot,
Lenny Challis.

___________________________

#!/usr/bin/perl -w

#this program takes in the input (html) file as command lines first argument
and output cgi file as second

use strict;

my $ofile = shift @ARGV;
my $cfile = shift @ARGV; #get the two filenames

open INPUT, "<", $ofile or die "Can't open $ofile: $!\n";
open OUTPUT, ">", $cfile or die "Can't open $cfile: $!\n"; #open
both files

print OUTPUT "\#!/usr/bin/perl\n\n";
print OUTPUT "print \"Content-type:text/html\\n\\n\";\n"; #print
the shebang and content tags

while (<INPUT>)
{
chomp($_); #getting rid of the \n's makes the code
alot more understandable
$_ =~ s/"/\\"/g; #first, escape
all quotes
$_ = "print \"" . $_ . "\\n\";\n"; #add print function
and newlines to $_
print OUTPUT $_; #add line to the output
file
}

print "Completed."; #let them know its
done

_____________________________

I am looking into getting in CGI and want to also get into mod_perl in the
future.

Thanks alot for your time.

Lenny Challis wrote:

> Good evening everyone.
>
> I am currently in college doing a National Diploma in computing. Most of the
> guys there haven't studied HTML or CSS or the likes and next year I think
> they may be asking us to do ASP. I'm not very fond of the idea at all, so I
> thought I would code my first assignment in Perl.

Excellent choice IMHO.


>
> I had to work with 2 friends however and they have never seen perl, or even

----------------------------------------------------------------^
The official correct name of the language is Perl.


> heard of it. In fact, the looks on peoples faces when I did a presentation
> on Larry Wall and Perl were kind of strange to say the least.
>
> Anyway, to the point. I am quite new to perl myself, but I absolutely adore
> it already. I am very keen to learn and make good habits from the very
> beginning. I hope you don't mind, but here is a program I have made in Perl
> to convert HTML files into CGI. I will use this while working with my
> friends.
>
> I would love to accept any criticism's. It is one of my first programs, but
> don't miss anything. One thing I hate is getting into bad habits, so I would
> like to pick them up now.
>
> Anyway, here goes.
> Thanks alot,
> Lenny Challis.
>
> ___________________________
>
> #!/usr/bin/perl -w

------------------^^
Excellent!


>
> #this program takes in the input (html) file as command lines first argument
> and output cgi file as second

--^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Commentary wrapped somewhere between your posting and my reading. Try
to avoid posting commentary (or code) which wraps.


>
> use strict;

--^^^^^^^^^^
Outstanding!


>
> my $ofile = shift @ARGV;
> my $cfile = shift @ARGV; #get the two filenames
>
> open INPUT, "<", $ofile or die "Can't open $ofile: $!\n";
> open OUTPUT, ">", $cfile or die "Can't open $cfile: $!\n"; #open
> both files
>
> print OUTPUT "\#!/usr/bin/perl\n\n";

----------------^
It is not necessary to escape a # character in a qq() string.


> print OUTPUT "print \"Content-type:text/html\\n\\n\";\n"; #print
> the shebang and content tags
>
> while (<INPUT>)
> {
> chomp($_); #getting rid of the \n's makes the code

--^-----^^
It is usually good style to indent the bodies of loops by four
characters. Makes it much more readable.

Also, $_ is the default argument to chomp, so you can say just:

chomp;

Likewise $_ can be omitted in many other places, like the next
statement, which could be just s/"/\\"/g; . That is usually the Perlish
thing to do.


> alot more understandable
> $_ =~ s/"/\\"/g; #first, escape
> all quotes
> $_ = "print \"" . $_ . "\\n\";\n"; #add print function

-----------------^^^^^^^^
Here you could "interpolate" $_ into the string, as in:

$_ = "print \"$_\\n\";\n";

Any scalar variable appearing in a "-string is substituted into the
string, so:

$v='y';
print "x $v z\n";

prints

x y z

That is why there are "-strings in addition to '-strings, and why they
aren't the same.

> and newlines to $_
> print OUTPUT $_; #add line to the output
> file
> }
>
> print "Completed."; #let them know its

-------------------^
Depending on your OS, you might want a \n at the end of this string to
avoid having a command prompt following the output on the same line.


> done
>
> _____________________________
>
> I am looking into getting in CGI and want to also get into mod_perl in the
> future.
>
> Thanks alot for your time.


You're welcome. Looks to me like you did a fine job on your Perl
program. Hope you find Perl as fascinating and useful as I do.

--
Bob Walton
Email: http://bwalton.com/cgi-bin/emailbob.pl

"Lenny Challis" <> wrote in message
news:br5qmj$fp8$...
>
> #!/usr/bin/perl -w
>
> #this program takes in the input (html) file as command lines first
argument
> and output cgi file as second
>
> use strict;

Very nice beginning.

>
> my $ofile = shift @ARGV;
> my $cfile = shift @ARGV; #get the two filenames
>

unless (scalar(@ARGV) == 2) {

die "Correct usage: perl myscript.pl input_file output_file\n";

}

my ($ofile, $cfile) = @ARGV;

You're better off checking your arguments before you try processing them.
Saves the user having to guess why the script might not be running. Also,
strange names for an input file and output file. It might make more sense to
call them $infile and $outfile so you don't confuse yourself later on. It
also helps when you have to come back to your code somewhere down the line
(or when someone else does).

> open INPUT, "<", $ofile or die "Can't open $ofile: $!\n";
> open OUTPUT, ">", $cfile or die "Can't open $cfile: $!\n"; #open
> both files
>
> print OUTPUT "\#!/usr/bin/perl\n\n";

print OUTPUT "#!/usr/bin/perl\n\n"; # no need to escape a # within quotes

> print OUTPUT "print \"Content-type:text/html\\n\\n\";\n";
#print
> the shebang and content tags
>

print OUTPUT 'print "Content-type: text/html\n\n";' . "\n";

Don't use double-quotes unless you need them.

> while (<INPUT>)

while (my $line = <INPUT>) {
....

Better to name your variables. It's okay to use $_ for a very small block,
but it's easy to forget what you're operating on and what $_ might be set
to.

Not an exhaustive review, but hope that gives you a few things to think
about.

Matt

<snip>
>Bob Walton Wrote:
>
>
> You're welcome. Looks to me like you did a fine job on your Perl
> program. Hope you find Perl as fascinating and useful as I do.
>
> --
> Bob Walton
> Email: http://bwalton.com/cgi-bin/emailbob.pl
>

I have been practicing making the shorter scripts (ie: not having to write
$_). Also, I know all about interpolating, I jut didn't think of doing it
this way (TMTOWTDI!).

Theres plenty to remember but it's such a versatile language and its so much
fun to learn. I have programmed C++, Visual Basic and a couple others, Perl
is my favourite by far. I am slowly getting my head into perl mode and yes I
_am_ finding it really useful.

Thanks for the great feedback.
Lenny

On Wed, 10 Dec 2003 00:51:29 -0000,
Lenny Challis <> wrote:
>
> I would love to accept any criticism's. It is one of my first programs, but
> don't miss anything. One thing I hate is getting into bad habits, so I would
> like to pick them up now.
>
> Anyway, here goes.
> Thanks alot,
> Lenny Challis.
>
> ___________________________
>
> #!/usr/bin/perl -w
>
> #this program takes in the input (html) file as command lines first argument
> and output cgi file as second
>
> use strict;

Warnings and strictures are good

>
> my $ofile = shift @ARGV;
> my $cfile = shift @ARGV; #get the two filenames
>
> open INPUT, "<", $ofile or die "Can't open $ofile: $!\n";
> open OUTPUT, ">", $cfile or die "Can't open $cfile: $!\n"; #open
> both files

Watch your line wrapping, I realise it's probably a posting to usenet
artifact, but even so some of the following lines are far too long, in
my opinion anyway.

I'd put single quotes aroung the < and >, since they don't need
double quote features. I'd leave off the \n on the die output so
that perl will add the line number information (which may of course
not be wanted in your case).

>
> print OUTPUT "\#!/usr/bin/perl\n\n";
> print OUTPUT "print \"Content-type:text/html\\n\\n\";\n"; #print
> the shebang and content tags

# isn't special and doesn't need to be escaped in a double quoted string.

Why no warnings and strictures in the generated code?

If you are putting "s in a string then it is usually best to use a different
quote character than ". Saves on the escaping, something like:

print OUTPUT 'print "Content-type:text/html\n\n";', "\n";

or if you really must have it as one string (but I'd rather avoid the
\\s):

print OUTPUT qq{print "Content-type:text/html\\n\\n";\n};

>
> while (<INPUT>)
> {
> chomp($_); #getting rid of the \n's makes the code
> alot more understandable
> $_ =~ s/"/\\"/g; #first, escape
> all quotes

If you are using $_ there is not need to mention it, just use
s/"/\\"/g, if you want to be explicit about the variable than don't
use $_, read into $line or something...

> $_ = "print \"" . $_ . "\\n\";\n"; #add print function
> and newlines to $_
> print OUTPUT $_; #add line to the output
> file

You seem to be producing an output file that is a CGI script that will
output the input file when run. However, if there are \ characters in the
input file things could go wrong.

Try running it on a file containing

\"

in it somewhere to see the problem.

And what about files containing things like:

Bananas only $1.99 a kilo, save $$. email:

You need to escape a lot more characters than just ".

Something like (completely untested):

s/\\/\\\\/g; #this must be done first, before we add \s
s/"/\\"/g;
s/\$/\\\$/g;
s/@/\\\@/g; # I prefer \@ in the pattern, but it isn't needed
s/\t/\\t/g;
s/\r/\\r/g;
print qq{print "$_\\n";\n};


> }
>
> print "Completed."; #let them know its
> done

You should close the OUTPUT file, and check for failure. After all
writes can actually fail (the disk might fill up, for example) and
it's good to check that the output file closed successfully (you could
check on all the print calls, but that would be ugly and unwarranted
in this case).

The loop could be replaced with:

print OUTPUT "print <<'HTML';\n";
print OUTPUT while (<INPUT>);
print OUTPUT "HTML\n";

Assuming the string 'HTML' isn't found on a line by itself in the input
and that the final line of input does end with a newline character.

But that probably misses the point of introducing some perl features.

As an aside, for those who might know:

Why is
print "@";
OK, but
print "$";
isn't?

To me the first should be illegal (but I'm clearly wrong).

--
Sam Holden

Lenny Challis wrote:
> I would love to accept any criticism's.

Okay, these are my comments:

> #!/usr/bin/perl -w

You may want to consider the lexically scoped warnings pragma before
the dynamically scoped -w switch.

#!/usr/bin/perl
use warnings;

See http://www.perldoc.com/perl5.8.0/pod/perllexwarn.html

> print OUTPUT "print \"Content-type:text/html\\n\\n\";\n";

You should learn the difference between ' and ", and consider using '
sometimes to reduce the need to escape things. For instance, that line
could be written:

print OUTPUT 'print "Content-type: text/html\n\n";', "\n";

Personally I think it makes it easier to read. See
http://www.perldoc.com/perl5.8.0/pod...#q%2DSTRING%2D

> while (<INPUT>)
> {
> chomp($_);
> $_ =~ s/"/\\"/g;
> $_ = "print \"" . $_ . "\\n\";\n";
> print OUTPUT $_;
> }

The here-document syntax is very useful when printing HTML. Those
lines could be replaced with:

print OUTPUT "print <<HTML;\n";
print OUTPUT $_ while <INPUT>;
print OUTPUT "\nHTML\n";

See http://www.perldoc.com/perl5.8.0/pod...html#%3c%3cEOF

Also, you should make it a habit to close filehandles when you no
longer need them:

close INPUT or die $!;
close OUTPUT or die $!;

> I am looking into getting in CGI

When dealing with CGI, you may want to benefit from some of the tools
in the CGI.pm module. (But don't forget to learn the basics about
what's going on behind the scenes.)

http://www.perldoc.com/perl5.8.0/lib/CGI.html

Good luck!

--
Gunnar Hjalmarsson
Email: http://www.gunnar.cc/cgi-bin/contact.pl

On 09 Dec 2003, "Lenny Challis" <> wrote in
comp.lang.perl.misc:

<snip>

> I would love to accept any criticism's. It is one of my first
> programs, but don't miss anything. One thing I hate is getting into
> bad habits, so I would like to pick them up now.

You'd like to pick up bad habits? Hmmm...

> #!/usr/bin/perl -w
>
> #this program takes in the input (html) file as command lines first
> argument and output cgi file as second

# Consider cutting your comments at a reasonable length (around 80
# characters) and continuing on the next line instead of letting your
# newsreader or text editor do the wrapping for you.

Also, rather than using the -w switch, use the warnings pragma instead
(see below).

>
> use strict;
use warnings;

>
> my $ofile = shift @ARGV;
> my $cfile = shift @ARGV; #get the two filenames

If no arguments are passed to shift(), it assumes @ARGV (or @_ in
subroutines), so either:

my $ofile = shift;
my $cfile = shift;

or

# preferred when there are many arguments
my ($ofile, $cfile) = @ARGV;

> open INPUT, "<", $ofile or die "Can't open $ofile: $!\n";
> open OUTPUT, ">", $cfile or die "Can't open $cfile: $!\n";
> #open both files

Note that the newline at the end of your die-string supresses the
filename and line number in the error message. For such a small script,
it's not a big deal, but there's no reason to ignore it.

> print OUTPUT "\#!/usr/bin/perl\n\n";
> print OUTPUT "print \"Content-type:text/html\\n\\n\";\n";
> #print the shebang and content tags

No need to escape '#' characters. You can also avoid interpolation
altogether by using single quotes:

print OUTPUT 'print "Content-type:text/html\n\n";', "\n";

> while (<INPUT>)
> {
> chomp($_); #getting rid of the \n's makes the
> code alot more understandable
> $_ =~ s/"/\\"/g; #first,
> escape all quotes
> $_ = "print \"" . $_ . "\\n\";\n"; #add print
> function and newlines to $_
> print OUTPUT $_; #add line to the
> output file
> }
>
> print "Completed."; #let them
> know its done

chomp() and s/// both operate on $_ by default:

while (<INPUT>){
chomp;
s/"/\\"/g;
# ...
}

Overall it looks fine to me. I'm somewhat new as well (but not as new
as you . Style-wise, though, I would suggest removing a lot of the
superfluous commenting, and make sure you indent your blocks properly.
Keep reading clpm and you can't help but learn.

Brandan L.
--
bclennox AT eos DOT ncsu DOT edu

"Sam Holden" <> wrote in message
news:. ..
>
> As an aside, for those who might know:
>
> Why is
> print "@";
> OK, but
> print "$";
> isn't?
>

$" is a predefined variable. How would you then use it in a double-quoted
string if the above were not an error?

Matt

"Sam Holden" <> wrote in message
news:. ..
> On Wed, 10 Dec 2003 00:51:29 -0000,
> Lenny Challis <> wrote:
> >
> > I would love to accept any criticism's. It is one of my first programs,
but
> > don't miss anything. One thing I hate is getting into bad habits, so I
would
> > like to pick them up now.
> >
> > Anyway, here goes.
> > Thanks alot,
> > Lenny Challis.
> >
> > ___________________________
> >
> > #!/usr/bin/perl -w
> >
> > #this program takes in the input (html) file as command lines first
argument
> > and output cgi file as second
> >
> > use strict;
>
> Warnings and strictures are good
>
> >
> > my $ofile = shift @ARGV;
> > my $cfile = shift @ARGV; #get the two filenames
> >
> > open INPUT, "<", $ofile or die "Can't open $ofile: $!\n";
> > open OUTPUT, ">", $cfile or die "Can't open $cfile: $!\n"; #open
> > both files
>
> Watch your line wrapping, I realise it's probably a posting to usenet
> artifact, but even so some of the following lines are far too long, in
> my opinion anyway.
>
> I'd put single quotes aroung the < and >, since they don't need
> double quote features. I'd leave off the \n on the die output so
> that perl will add the line number information (which may of course
> not be wanted in your case).
>
> >
> > print OUTPUT "\#!/usr/bin/perl\n\n";
> > print OUTPUT "print \"Content-type:text/html\\n\\n\";\n";
#print
> > the shebang and content tags
>
> # isn't special and doesn't need to be escaped in a double quoted string.
>
> Why no warnings and strictures in the generated code?
>
> If you are putting "s in a string then it is usually best to use a
different
> quote character than ". Saves on the escaping, something like:
>
> print OUTPUT 'print "Content-type:text/html\n\n";', "\n";
>
> or if you really must have it as one string (but I'd rather avoid the
> \\s):
>
> print OUTPUT qq{print "Content-type:text/html\\n\\n";\n};
>
> >
> > while (<INPUT>)
> > {
> > chomp($_); #getting rid of the \n's makes the
code
> > alot more understandable
> > $_ =~ s/"/\\"/g; #first,
escape
> > all quotes
>
> If you are using $_ there is not need to mention it, just use
> s/"/\\"/g, if you want to be explicit about the variable than don't
> use $_, read into $line or something...
>
> > $_ = "print \"" . $_ . "\\n\";\n"; #add print
function
> > and newlines to $_
> > print OUTPUT $_; #add line to the
output
> > file
>
> You seem to be producing an output file that is a CGI script that will
> output the input file when run. However, if there are \ characters in the
> input file things could go wrong.
>
> Try running it on a file containing
>
> \"
>
> in it somewhere to see the problem.
>
> And what about files containing things like:
>
> Bananas only $1.99 a kilo, save $$. email:
>
> You need to escape a lot more characters than just ".
>
> Something like (completely untested):
>
> s/\\/\\\\/g; #this must be done first, before we add \s
> s/"/\\"/g;
> s/\$/\\\$/g;
> s/@/\\\@/g; # I prefer \@ in the pattern, but it isn't needed
> s/\t/\\t/g;
> s/\r/\\r/g;
> print qq{print "$_\\n";\n};
>
>
> > }
> >
> > print "Completed."; #let them know
its
> > done
>
> You should close the OUTPUT file, and check for failure. After all
> writes can actually fail (the disk might fill up, for example) and
> it's good to check that the output file closed successfully (you could
> check on all the print calls, but that would be ugly and unwarranted
> in this case).
>
> The loop could be replaced with:
>
> print OUTPUT "print <<'HTML';\n";
> print OUTPUT while (<INPUT>);
> print OUTPUT "HTML\n";
>
> Assuming the string 'HTML' isn't found on a line by itself in the input
> and that the final line of input does end with a newline character.
>
> But that probably misses the point of introducing some perl features.
>
> As an aside, for those who might know:
>
> Why is
> print "@";
> OK, but
> print "$";
> isn't?
>
> To me the first should be illegal (but I'm clearly wrong).
>
> --
> Sam Holden
>

That was really great feedback.
I have learnt alot from it, Thanks alot

Lenny

Sam Holden wrote:
> You need to escape a lot more characters than just ".
>
> Something like (completely untested):
>
> s/\\/\\\\/g; #this must be done first, before we add \s
> s/"/\\"/g;
> s/\$/\\\$/g;
> s/@/\\\@/g; # I prefer \@ in the pattern, but it isn't needed
> s/\t/\\t/g;
> s/\r/\\r/g;
> print qq{print "$_\\n";\n};

<snip>

> The loop could be replaced with:
>
> print OUTPUT "print <<'HTML';\n";
------------------------^----^

Which is a much smarter way to deal with the need for escaping things.

--
Gunnar Hjalmarsson
Email: http://www.gunnar.cc/cgi-bin/contact.pl