Question

I have a very basic confusion about grep. Suppose I have a following file to grep in:

test.txt:
This is an article 
from some newspaper
Article is good 
newspaper is not.

Now if I grep with following expression

grep -P "is\s*g" test.txt

I get the line:

Article is good

However if I do this:

grep -P "is*g" test.txt

I don’t get anything. My question is since asterix (*) is a wildcard which represents 0 or more repetitions of the previous character, shouldn’t the output of grep be the same. Why the zero or more repetitions of ‘s’ is not giving any output?

What am I missing here. Thanks for the help!

Answer 1

Because there’s nothing in your input that matches i, then 0 or more repetitions of s, then g. “Article is good” can’t match because it has a space after the s, not a g. The pattern is\s*g matches because \s is a special pattern that matches any sort of whitespace — so the overall pattern is is, then any amount of space, then g, which naturally matches “is g”.