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Top Forums Shell Programming and Scripting Delete all lines except a line starting with string Post 303016027 by omega3 on Wednesday 18th of April 2018 10:40:29 AM
Old 04-18-2018
Delete all lines except a line starting with string

Shell : bash
OS : RHEL 6.8

I have a file like below.

Code:
$ cat pattern.txt
hello
txt1
txt2
txt3
some other text
txt4

I want to remove all lines in this file except the ones starting with txt . How can I do this ?
 

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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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