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Top Forums Shell Programming and Scripting Problem with pipes on infinite streams Post 302408049 by alister on Saturday 27th of March 2010 11:51:15 PM
Old 03-28-2010
You can run the stream generator in the background, asynchronously, and use a named pipe to communicate with it:
Code:
mkfifo sg_pipe
stream_generator > sg_pipe &
head -n1 sg_pipe
kill %?stream

Regards,
Alister

---------- Post updated at 10:51 PM ---------- Previous update was at 10:38 PM ----------

For the example code you used in your original post:
Code:
#!/bin/bash
counter() {
  seq 1000 | while read NUM; do
    echo $NUM
    echo "debug: $NUM" >&2 
    sleep 0.1 # slow it down so we know when this loop really ends
  done
}

mkfifo p
counter | grep --line-buffered "[27]" > p &
head -n1 p
kill %?counter

Outputs:
Code:
$ ./tokland.sh 
debug: 1
debug: 2
2

Alister
 

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IO::Async::Protocol::LineStream(3pm)			User Contributed Perl Documentation		      IO::Async::Protocol::LineStream(3pm)

NAME
"IO::Async::Protocol::LineStream" - stream-based protocols using lines of text SYNOPSIS
Most likely this class will be subclassed to implement a particular network protocol. package Net::Async::HelloWorld; use strict; use warnings; use base qw( IO::Async::Protocol::LineStream ); sub on_read_line { my $self = shift; my ( $line ) = @_; if( $line =~ m/^HELLO (.*)/ ) { my $name = $1; $self->invoke_event( on_hello => $name ); } } sub send_hello { my $self = shift; my ( $name ) = @_; $self->write_line( "HELLO $name" ); } This small example elides such details as error handling, which a real protocol implementation would be likely to contain. DESCRIPTION
EVENTS
The following events are invoked, either using subclass methods or CODE references in parameters: on_read_line $line Invoked when a new complete line of input is received. PARAMETERS
The following named parameters may be passed to "new" or "configure": on_read_line => CODE CODE reference for the "on_read_line" event. METHODS
$lineprotocol->write_line( $text ) Writes a line of text to the transport stream. The text will have the end-of-line marker appended to it; $text should not end with it. AUTHOR
Paul Evans <leonerd@leonerd.org.uk> perl v5.14.2 2012-10-24 IO::Async::Protocol::LineStream(3pm)
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