Having an option to write to a file or STDOUT 1

[wardy66]

Hi all

I'm trying to think of the best way to write a script that can either output to a file or to STDOUT if no file name is supplied.

For example,

script.pl -o file.txt

would send the output to a file but

script.pl

would just print to the screen.

Inside script.pl I was thinking of something along the lines of

if ( $OUTFILE ) {
  open OUT, $OUTFILE
}
else {
  OUT = *STDOUT
}

# Print to file or screen, depending on whether $OUTFILE is set
print OUT "Hello world\n";

but is this the right idea? What if I close OUT - is this "impolite" since it might be going to STDOUT

Any comments or improvements on my idea are very welcome

Thanks
~ Michael

 

[ishnid]

You can use the `select' function to change the default filehandle. Normally, when you call `print' without specifying a filehandle, it prints to STDOUT by default. `select' changes that. So:

open OUT, $OUTFILE;
select OUT;

print 'blah'; # this is printed to $OUTFILE

select STDOUT;
close OUT;

print 'blah'; # printed to STDOUT again

 

[KevinADC]

check the @ARGV array, if there is one then print to file, if not print to STDOUT.

 

[wardy66]

Thanks Kevin but I use Getopt::Std to process all sorts of command line options. In the real script there are 2 output files, one of which can optionally be STDOUT.

So I need to look at what's passed as the value of -p and then decide whether to print or not.

As I put in my example above, I can get it to work by doing something like OUT = *STDOUT but it seemed a touch evil.

I was wondering about select() and also if the "&" forms of open() might be wise too.

Thanks

 

[rharsh]

Why not something like the following?

if ($options{p} =~ /stdout/ || ! $options{p}) {
    select STDOUT;
} else {
    open FH, "< $options{p}" or die "Could not open file.\n$!\n";
    select FH;
}

This is untested; you might need to change the '|| !' bit to get the precedence right.

 

[wardy66]

Thanks rharsh

I like that one. Might start using it from now on

Thanks