Use of -z in while loop condition


 
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# 1  
Old 12-03-2010
Question Use of -z in while loop condition

Hi,

Could you please tell what is the meaning of -z in while loop condition.
For example,

while [ -z "$name" ]; do
echo "*** Enter the age "
readage
# 2  
Old 12-03-2010
-z means NULL

while [ -z "$name" ]; do means while value of $name is null.
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# 3  
Old 12-03-2010
Things inside brackets are a "test". -z tests "$name" to see if its length is zero.

from "man test":
-z String1
Returns a True exit value if the length of the String1 variable is
0 (zero).
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# 4  
Old 12-03-2010
-z string Comparison option

usage : -z <string_name>

meaning: <string_name> is NULL and does exist

it is used in if,while ,....
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