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Top Forums UNIX for Dummies Questions & Answers stuck and confused Post 302135182 by cfajohnson on Thursday 6th of September 2007 04:53:17 PM
Old 09-06-2007
Quote:
Originally Posted by iago
can it be done without using sed or awk?


Using head and tail:
Code:
lines=$( wc -l < "$2" )
middle=$(( $lines / 2 ))

n=0
{
   head -n "$middle" "$2"
   printf "%s\n" "$1"
   tail -n "$(( $middle + 1 ))" "$2"
} > tempfile

Without any external commands, it will be very slow on a long file:
Code:
lines=$( wc -l < "$2" )
middle=$(( $lines / 2 ))

n=0
while IFS= read -r line
do
   n=$(( $n + 1 ))
   printf "%s\n" "$line"
   [ $n -eq $middle ] && printf "%s\n" "$1"
done < "$2" > tempfile

Somewhat faster (it uses cat for the second half of the file):
Code:
while IFS= read -r line
do
   n=$(( $n + 1 ))
   printf "%s\n" "$line"
   [ $n -eq $middle ] && { printf "%s\n" "$1"; cat; exit; }
done < "$2"


Last edited by cfajohnson; 09-06-2007 at 06:13 PM..
 

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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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