Rules for Naming variable name
Variable name must begin with alphanumeric character or underscore character (_), followed by one or more alphanumeric or underscore characters. Valid shell variable examples:
HOME SYSTEM_VERSION vech no
Do not put spaces on either side of the equal sign when assigning value to variable. For example, the following is valid variable declaration:
However, any of the following variable declaration will result into an error such as command not found:
no =10 no= 10 no = 10
Variables names are case-sensitive, just like filenames.
no=10 No=11 NO=20 nO=2
All are different variable names, to display value 20 you've to use $NO variable:
echo "$no" # print 10 but not 20 echo "$No" # print 11 but not 20 echo "$nO" # print 2 but not 20 echo "$NO" # print 20
You can define a NULL variable as follows (NULL variable is variable which has no value at the time of definition):
Try to print its value by issuing the following command:
Do not use ?,* and other special characters, to name your variable.
?no=10 #invalid out*put=/tmp/filename.txt #invalid _GREP=/usr/bin/grep #valid echo "$_GREP"