grep does not accept \t, unless you use the -P option for perl compatible regexps (it is available only in GNU grep, anyway). Therefore you have to use the [:space:] pattern or type a literal TAB using Ctrl-V + TAB:
Code:
grep '[ = ]fun' file
On the other hand, awk and sed (and obviously perl) interpret \t correctly:
Code:
awk '/[\t= ]fun/' file
sed -n '/[\t= ]fun/p' file