Question

What is difference between

grep -isn "String\.format" -R .

and

grep -isn String\.format -R .

When I use the latter, the results include String format and String.format, but if I use the former, the results only include String.format. This result is same as using

grep -isn 'String\.format' -R .

Can anyone give an explanation?

Answer 1

Without quotation marks, the shell interprets \. as a . before passing the string to grep. So grep now has a regular expression wildcard and can thus find any character, including a space.

When you included quotation marks, the shell passed the full \. to grep. Now grep knows that it must search for a period, and not a wildcard.