sending output to STDOUT or a file

[Vahid]

Hi,
I have a program that generates some output but I need it to dump them
to a file if ran in a background and print on screen if ran in
foreground. This is a sample program that need some help with:
#!/bin/perl
#
use warnings;
use strict;
#
my $today=`date +%Y%m%d`; chomp $today;
my $LOG="/tmp/output.$today.log";
my $foreground="$LOG";
if ( -t STDOUT) {
$foreground=STDOUT;
}
open (LOGfh, "> $foreground") or die "ERROR: $!";

print LOGfh "The foreground is $foreground\n";
close LOGfh;

Of course this will give me error for using STDOUT in open.
Thanks,

 

[xhoster]

Hi,
I have a program that generates some output but I need it to dump them
to a file if ran in a background and print on screen if ran in
foreground. This is a sample program that need some help with:
#!/bin/perl
#
use warnings;
use strict;
#
my $today=`date +%Y%m%d`; chomp $today;
my $LOG="/tmp/output.$today.log";
my $foreground="$LOG";
if ( -t STDOUT) {
$foreground=STDOUT;
}
open (LOGfh, "> $foreground") or die "ERROR: $!";

print LOGfh "The foreground is $foreground\n";
close LOGfh;

Of course this will give me error for using STDOUT in open.
Thanks,

Maybe I'm missing something, but I think this does it:

unless ( -t STDOUT) {
my $today=`date +%Y%m%d`; chomp $today;
open STDOUT, ">/tmp/output.$today.log" or die $!;
};

print "The foreground is $foreground\n";

Xho

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[John W. Krahn]

Hi,
I have a program that generates some output but I need it to dump them
to a file if ran in a background and print on screen if ran in
foreground. This is a sample program that need some help with:
#!/bin/perl
#
use warnings;
use strict;
#
my $today=`date +%Y%m%d`; chomp $today;

use POSIX 'strftime';

my $today = strftime '%Y%m%d', localtime;

my $LOG="/tmp/output.$today.log";
my $foreground="$LOG";

my $foreground = $LOG;

perldoc -q quoting

if ( -t STDOUT) {
$foreground=STDOUT;
}
open (LOGfh, "> $foreground") or die "ERROR: $!";

print LOGfh "The foreground is $foreground\n";
close LOGfh;

Of course this will give me error for using STDOUT in open.

perldoc -q "How can I use a filehandle indirectly"
perldoc -q "How do I make an array of filehandles"
perldoc -f open
perldoc perlopentut



John

 

[comp.llang.perl.moderated]

Hi,
I have a program that generates some output but I need it to dump them
to a file if ran in a background and print on screen if ran in
foreground. This is a sample program that need some help with:
#!/bin/perl
#
use warnings;
use strict;
#
my $today=`date +%Y%m%d`; chomp $today;
my $LOG="/tmp/output.$today.log";
my $foreground="$LOG";
if ( -t STDOUT) {
$foreground=STDOUT;}

open (LOGfh, "> $foreground") or die "ERROR: $!";

print LOGfh "The foreground is $foreground\n";
close LOGfh;

Of course this will give me error for using STDOUT in open.

Another possibility:

if ( -t STDOUT ) {
print ...
} else {
open ( local *STDOUT, '>', $LOG ) or die $!;
print STDOUT ...
}

 

[Vahid Moghaddasi]

Maybe I'm missing something, but I think this does it:

unless ( -t STDOUT) {
my $today=`date +%Y%m%d`; chomp $today;
open STDOUT, ">/tmp/output.$today.log" or die $!;

};

print "The foreground is $foreground\n";

Xho

Yes that does the trick, thank you.
I don't understand how does the output of the last print statement
goes to STDOUT if the program is running in the background?

 

[xhoster]

Yes that does the trick, thank you.
I don't understand how does the output of the last print statement
goes to STDOUT if the program is running in the background?

Sorry, I don't understand the question. Maybe you are confusing
STDOUT with the terminal. Often STDOUT is hooked up to the terminal,
but sometimes it is not.

The concept of "background" is somewhat fuzzy. In Linux, if you start a
program "in the background" by adding a &, that doesn't change the STDOUT
of the program. For example, the below prints "1" because the program's
STDOUT is still the terminal, despite being run in the background.

perl -le 'sleep 3; print -t STDOUT' &

Where as this doesn't print "1", because it's STDOUT is not the terminal,
even though it is running in the foreground;

perl -le 'warn -t STDOUT' > /dev/null

Xho

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