I/O redirection in perl

[harishram]

Hi,

This piece of code works fine..the output is redirected correctly to mytest.out

#!/usr/bin/perl
$TEST="2005";
system("echo $TEST > mytest.out");

But the below piece of code does not work..the output file mytest.out is empty and display comes on the screen.

Assumption: The file "input" contains string 2005

#!/usr/bin/perl
open (TXNFILE, "input");
$TEST=<TXNFILE>;
system("echo $TEST > mytest.out");

Can someone please tell me why.

Thanks

 

[dmazzini]

open( INFILE, "toread.txt" )
or die( "Can not open toread.txt: $!" );

open( OUTFILE, ">towrite.txt" )
or die( "Can not open towrite.txt: $!" );

@contents=<INFILE>;
print OUTFILE @contents;


close( INFILE );
close( OUTFILE );

dmazzini
GSM System and Telecomm Consultant

 

[harishram]

Hi dmazzini,

Thanks for ur reply. Let me give a clearer picture of what i was trying to do..i am trying to execute a program CreateTemplate with $TRNXID as a parameter and i want the output to go to the file mytest.out.

system("/usr/bin/java CreateTemplate -tranId $TRNXID > mytest.out");

The output is coming onto the screen but is not going to mytest.out.
can u tell me why this is not working and how do i overcome it.

Thanks

 

[duncdude]

how about:-

1) assigning the result of the system call to a scalar
2) write the contents of the scalar to your output file

$result = system("/usr/bin/java CreateTemplate -tranId $TRNXID");

open (OUT, "> mytest.out");
print OUT $result;
close OUT;

Kind Regards
Duncan

 

[TrojanWarBlade]

Sorry duncdeude,
I think you got that one wrong. You're gonna be writing out the return code and not the output of the command.
Why is no-one suggesting opening a pipeline?

#!/usr/bin/perl -w
use strict;

open IN, "/usr/bin/java CreateTemplate -tranId $TRNXID |"
     or die "Failed to open CreateTemplate";
open OUT, ">mytest.out" or die "Failed to create logfile";
print OUT while(<IN>);
close OUT;
close IN;

(very injured) Trojan.

 

[duncdude]

Hi Trojan

Blimey - i am not awake this morning!

O.K. - is that because nothing will happen when run from the command line? i.e. no output to the screen is generated?


Kind Regards
Duncan

 

[TrojanWarBlade]

No, the system command returns the exit code of the process (integer 0-255), to get the stdout, use backticks or as in my case, a pipeline.


(very injured) Trojan.

 

[duncdude]

Well - they say you learn something every day... and it's only 7:40 a.m. and i've learnt somehing already!

I always assumed that system("") was the same as backticks... probably because i never use system("")

I am a muppet!

Thanks Trojan


Kind Regards
Duncan

 

[harishram]

Hi Trojan,

Thanks for the solution. It worked fine..but had a question..In the file open command what is the significance of "|" at the end.

Thanks

 

[TrojanWarBlade]

The "|" char changes the open from a file open to a pipeline open.




(very injured) Trojan.