LinuxQuestions.org
View the Most Wanted LQ Wiki articles.
Go Back   LinuxQuestions.org > Blogs > linux-related notes
User Name
Password

Notices

Just annotations of little "how to's", so I know I can find how to do something I've already done when I need to do it again, in case I don't remember anymore, which is not unlikely. Hopefully they can be useful to others, but I can't guarantee that it will work, or that it won't even make things worse.
Rate this Entry

Give a default/non-null value in order to avoid the "unary operator expected" error

Posted 02-19-2014 at 03:00 PM by the dsc
Tags bash

Quote:
Originally Posted by cfajohnson
Quote:
i am trying to compare a value with value 50. but i am getting
"[: -lt: unary operator expected"

I am using

if [ $j -lt 50 ]
then
echo "------------"

fi
Make sure that $j expands to a value. Best is to set it explicitly, but you can also give it a default value (0 in this example):


Code:
if [ ${j:-0} -lt 50 ]
http://www.unix.com/302295072-post3.html

Zero, literally "0", is not the same as "", but actually a value, and conversely "" isn't "0".

I never understood the problem exactly, I thought that it had to do with not using quotes for some reason, and used to "cheat" with double checks. That thread explains that, when the variable is empty, the result is essentially "[ "" -lt 10 ]". Notice the empty quotes within the check; that's what happens when you add quotes, it really does not help at all would be the same as just "[ -lt 10]".
Posted in Uncategorized
Views 144 Comments 0
« Prev     Main     Next »
Total Comments 0

Comments

 

  



All times are GMT -5. The time now is 07:40 AM.

Main Menu

My LQ
Write for LQ
LinuxQuestions.org is looking for people interested in writing Editorials, Articles, Reviews, and more. If you'd like to contribute content, let us know.
Main Menu
Syndicate
RSS1  Latest Threads
RSS1  LQ News
Twitter: @linuxquestions
identi.ca: @linuxquestions
Facebook: linuxquestions Google+: linuxquestions
Open Source Consulting | Domain Registration