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Full Discussion: How to remove empty line.?
Top Forums Shell Programming and Scripting How to remove empty line.? Post 302975927 by Scrutinizer on Tuesday 21st of June 2016 02:46:32 PM
Old 06-21-2016
You are welcome. If you try:
Code:
( set -x; [ -n $p ] && [ -n "$p" ])
+ '[' -n ']'
+ '[' -n '' ']'

You'll notice that the first one evaluates to -n and the second one to -n ''

In the first case the there is no protection of variable p, which contains an empty field. Since there is not protective quotes around $p, the result is field split and since $p is empty this results in 0 fields. So wat remains "-n" which is a test if the string "-n" is non empty
([ "$somestring" ] if the same as [ -n "$somestring"], I prefer the latter for clarity, so in fact [ -n ] is equivalent to [ -n -n ])


In the second case the result of "$p" is not field split and so the -n is interpreted as an operator with one field as parameter, which contains an empty variable, and this evaluates to false .

So that is yet another reason to put quotes around variable expansions.

I hope this clarifies things...
Last edited by Scrutinizer; 06-21-2016 at 03:55 PM..
This User Gave Thanks to Scrutinizer For This Post:
ken6503
 

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LEARN ABOUT DEBIAN

lr_environment

LR_ENVIRONMENT.IN(1)					  LogReport's Lire Documentation				      LR_ENVIRONMENT.IN(1)

NAME

       lr_environment - Export Lire configuration in shell script form

SYNOPSIS

       eval `lr_environment`

DESCRIPTION

       The lr_environment command is used to import the Lire configuration in Lire shell scripts.

       All of Lire configuration variables will be written in a format that can be evaled by the shell.

       Shell scripts don't usually have to use that command, since it is done by the defaults file sourced by each command.

       The old names used by when the configuration was done in shell script are also exported by this script for backward compatibility.

AUTHOR

	 Francis J. Lacoste <flacoste@logreport.org>

VERSION

       $Id: lr_environment.in,v 1.12 2006/07/23 13:16:33 vanbaal Exp $

COPYRIGHT

       Copyright (C) 2003 Stichting LogReport Foundation LogReport@LogReport.org

       This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by
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       This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of
       MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more details.

       You should have received a copy of the GNU General Public License along with this program (see COPYING); if not, check with
       http://www.gnu.org/copyleft/gpl.html.

Lire 2.1.1							    2006-07-23						      LR_ENVIRONMENT.IN(1)
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