Question about grep & backreferences

opto · 01-20-2007, 11:32 PM

I am practicing using grep and trying to find the line with two occurrences of why in a file called learn_grep.txt. I thought I typed the proper commands, but according to my results I am not. Here is what the line looks like in the text file:

Quote:

why ask why

I type this into bash:

Code:

usr@terminal:$ grep \(why\).*\1 learn_grep.txt

It does not echo any line in learn_grep.txt.

I tried to look it using google.com/linux and linuxquestions.org but I could not find my problem.

Does anybody know what I am doing wrong?

Matir · 01-21-2007, 12:09 AM

Try putting quotes around your grep pattern to avoid shell expansion of special symbols in it.

opto · 01-21-2007, 12:24 AM

Code:

$ grep '\(why\).*\1' learn_grep.txt
why ask why

Man, forgot about the quotes. Thank you.