grep using octal patterns and avoid grep: Invalid back reference

Have you ever had a line in a file like this?

This line is fine
This line has  nasty character in it
This line is fine

And then after you read the man page for grep you may have tried this to grep these characters and gotten an error:

$ grep '\240' foo
grep: Invalid back reference

Well, try this instead:

$ grep $'\240' foo
This line has   nasty character in it

Hope that helps.

P.S. Here is a way to use octal dump (od) to figure out the octal value of the nasty character you are trying to match ... in this case it's the "240":

$ grep nasty foo | od -c
0000000 T h i s l i n e h a s 240 n
0000020 a s t y c h a r a c t e r i
0000040 n i t . \n
0000046