Re: peek at STDIN, to determine data type and then pass STDIN to a parser

Hello aral,

The ungets method from FileHandle::Unget works on STDIN:

#! perl
use strict;
use warnings;
use FileHandle::Unget;

$| = 1;

my $fh = FileHandle::Unget->new(\*STDIN)
  or die "Cannot open filehandle: $!";

print "\nEnter a string: ";
read($fh, my $buffer1, 10);
print "\nThe first  10 characters: '$buffer1'\n";

$fh->ungets($buffer1);

read($fh, my $buffer2, 15);
print "The \"next\" 15 characters: '$buffer2'\n";
$fh->close;
[download]

Output:

 1:17 >perl 1115_SoPW.pl

Enter a string: abcdefghijklmnopqrstuvwxyz

The first  10 characters: 'abcdefghij'
The "next" 15 characters: 'abcdefghijklmno'

 1:17 >
[download]

Update: Added print statements and renamed variables.

Hope that helps,

Athanasius <°(((>< contra mundum Iustus alius egestas vitae, eros Piratica,

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Re^2: peek at STDIN, to determine data type and then pass STDIN to a parser by ikegami (Patriarch) on Jan 07, 2015 at 15:33 UTC
I'd use IO::Unread instead since it uses Perl's builtin support for unreading rather than reimplementing every file operation.	[reply]
Re^2: peek at STDIN, to determine data type and then pass STDIN to a parser by aral (Acolyte) on Jan 08, 2015 at 09:43 UTC
Excellent solution as well - I just tested it and it worked out of the box like this: `use FileHandle::Unget; my $fh = FileHandle::Unget->new(\STDIN) or die "Cannot open filehandle: $!"; my $testline = <$fh>;; $fh->ungets($testline); print "$.: $testline"; for (my $i = 0; $i < 3; $i++) { $testline = <$fh>; print "$.: $testline"; }` [download] Output for "cat xmlfile \| ./perscript.pl" is: `1: <?xml version="1.0" encoding="UTF-8"?> 1: <?xml version="1.0" encoding="UTF-8"?> 2: <MFOP> 3: <Basics>` [download] Thank you very much! FileHandle::Unget is the* answer to my original question. @ikegami: Unfortunately, the install script (Makefile) for IO::Unread fails with error messages, and there seems to be no debian packet for it available in jessie - so I was not able to test this.	[reply] [d/l] [select]