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I have a short perl script, it goes like this:

#!/usr/bin/perl

$line = <STDIN>;
print $line;
`echo $line > output`;

I was expecting it to read a line from std. input, then output the line
to the screen and to a file named 'output'. When I try this, the
output file is always empty, even though the print statement works.
Can someone tell me why?

Thanks,

Ed

"Ed Mancebo" <> wrote in
news: oups.com:

> I have a short perl script, it goes like this:
>
> #!/usr/bin/perl
>
> $line = <STDIN>;
> print $line;
> `echo $line > output`;
>
> I was expecting it to read a line from std. input, then output the line
> to the screen and to a file named 'output'. When I try this, the
> output file is always empty, even though the print statement works.
> Can someone tell me why?

There is a newline at the end of $line.

Sinan

Ed Mancebo wrote:

> I have a short perl script, it goes like this:

Shelling out to call "echo" is quite possibly the most horribly inefficient
way I can imagine to store $line in a file. But I'm assuming that this is
just a minimal example as suggested in the posting guidelines, so I'm
answering the question as given, rather than suggesting an entirely
different approach.

> #!/usr/bin/perl

use warnings;
use strict;

> $line = <STDIN>;

my $line = <STDIN>;

# Or, more simply:

my $line = <>;

> print $line;
> `echo $line > output`;

Store and print the results of that command - I think you'll find it
enlightening.

my $output = `echo $line > output`;
print $output;

Then, have a look at "perldoc -f chomp" to find out how to get rid of the
trailing newline in $line.

(BTW, if you really *are* using backticks and echo to write to a file, you
have a *lot* to learn. Have a look at "perldoc perlopentut".)

sherm--

--
Cocoa programming in Perl: http://camelbones.sourceforge.net
Hire me! My resume: http://www.dot-app.org

On Tue, 11 Jan 2005 21:46:24 -0800, Ed Mancebo wrote:

> I have a short perl script, it goes like this:
>
> #!/usr/bin/perl
>
> $line = <STDIN>;
> print $line;
> `echo $line > output`;

Try using the system command instead of backticks.

#!/usr/bin/perl
use strict;
use warnings;

print "input something\n";
chomp(my $line = <STDIN>);
print "$line\n";
system "echo $line > output";


>
> I was expecting it to read a line from std. input, then output the line
> to the screen and to a file named 'output'. When I try this, the
> output file is always empty, even though the print statement works.
> Can someone tell me why?
>
> Thanks,
>
> Ed

Whitey Johnson wrote:

> On Tue, 11 Jan 2005 21:46:24 -0800, Ed Mancebo wrote:
>
>> I have a short perl script, it goes like this:
>>
>> #!/usr/bin/perl
>>
>> $line = <STDIN>;
>> print $line;
>> `echo $line > output`;
>
> Try using the system command instead of backticks.
>
> #!/usr/bin/perl
> use strict;
> use warnings;
>
> print "input something\n";
> chomp(my $line = <STDIN>);
> print "$line\n";
> system "echo $line > output";

Your code is correct - but your explanation is not. It's the chomp() in your
version that's making the difference, not your use of system() instead of
backticks.

sherm--

--
Cocoa programming in Perl: http://camelbones.sourceforge.net
Hire me! My resume: http://www.dot-app.org

On Wed, 12 Jan 2005 13:50:16 -0500, Sherm Pendley wrote:

<snip>
>
> Your code is correct - but your explanation is not. It's the chomp() in your
> version that's making the difference, not your use of system() instead of
> backticks.
>
> sherm--

My bad. I saw that explained in the other email and didn't think it needed
rementioning. Now looking back at my email it does look like I am trying
to say that the system command is what would fix the OP's problem. Thanks.

Whitey Johnson <> wrote:

> in the other email

> looking back at my email


This is NOT email.

This is Usenet.

They are not the same, and the difference makes a difference!


--
Tad McClellan SGML consulting
Perl programming
Fort Worth, Texas