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Top Forums Shell Programming and Scripting Value of variable is NULL, but test doesn't seem to recognize Post 302623635 by intelinside on Saturday 14th of April 2012 07:26:38 AM
Old 04-14-2012
Value of variable is NULL, but test doesn't seem to recognize

Hello, Unix-forums!

My problem:
Code:
read -p "Enter any number, please" number
sleep 1
echo $number | tr -d 0-9
test -z $number && echo "Thank you" || echo "This is not a number"

Test always displays "This is not a number". It doesn't matter if I entered a or 1.

But if I order
Code:
echo $number

before the test command, it displays nothing, so the $number should be NULL, not?

Last edited by intelinside; 04-14-2012 at 08:37 AM..
 

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EMPTY-PAGE(1)							 ExactImage Manual						     EMPTY-PAGE(1)

NAME
empty-page - empty page detector of the ExactImage toolkit SYNOPSIS
empty-page [option...] {-i | --input} input-file empty-page {-h | --help} DESCRIPTION
ExactImage is a fast C++ image processing library. Unlike many other library frameworks it allows operation in several color spaces and bit depths natively, resulting in low memory and computational requirements. empty-page counts dark pixels of a black and white image and decides with a threshold whether the page is most probably empty, and thus can be removed from the image processing stream. OPTIONS
-i file, --input file Read image from the specified file. -m n, --margin n Set width of border margin to skip. For speed reasons, the margin has to be a multiple of 8. The default is 16. -p x, --percentage x Set fraction of permissible dark pixels. The default is 0.05 (5%). -h, --help Display help text and exit. EXAMPLES
$ empty-page -i test.tif The image has 75461 dark pixels from a total of 1060992 (7.11231%). non-empty EXIT STATUS
The exit status is 0 if the image is mostly white, 1 otherwise. SEE ALSO
exactimage(7) AUTHORS
Jakub Wilk <jwilk@debian.org> Wrote this manual page for the Debian system. http://www.exactcode.de/site/open_source/exactimage/ This manual page incorporates texts found on the ExactImage homepage. COPYRIGHT
This manual page was written for the Debian system (and may be used by others). Permission is granted to copy, distribute and/or modify this document under the terms of the GNU General Public License, Version 2 or (at your option) any later version published by the Free Software Foundation. On Debian systems, the complete text of the GNU General Public License can be found in /usr/share/common-licenses/GPL-2. empty-page 09/09/2013 EMPTY-PAGE(1)
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