How to filter a null variable.

Shell Programming and Scripting
1

I have the necessity to use this command:

cat file1 | grep $A | grep $B

where sometime A and, or, B are not set.

For example:
I set A=@
never defined or set B

The above command send a cat error.

Any idea?
Thanks.

            Giovanni
2

2 things.

check out egrep.

cat file|egrep $A\|$B

when you declare $A or $B if you use a meta charicter make sure you backslash it to remove its special meaning.

[qgatu003]/export/home/mxdooley$cat test.file|egrep $A\|$B
@this is a test2
[qgatu003]/export/home/mxdooley$echo $A
@
[qgatu003]/export/home/mxdooley$