How to grep asterisk without escaping?

Question

Suppose I have a file abc.txt which contains line ab*cd. When I grep that pattern ab*cd with quotes but without escaping the asterisk it does not work:

> grep ab*c abc.txt 
> grep "ab*c" abc.txt 
> grep 'ab*c' abc.txt 

When I use both quotes and escaping it does work

> grep "ab\*c" abc.txt 
ab*cd
> grep 'ab\*c' abc.txt 
ab*cd

Now I wonder why the quotes do not work and if I can use only quotes without escaping the asterisk.

Answer 1

Use the flag -F to search for fixed strings -- instead of regular expressions. From man grep:

   -F, --fixed-strings
          Interpret  PATTERN  as  a  list  of  fixed strings, separated by
          newlines, any of which is to be matched.  (-F  is  specified  by
          POSIX.)

For example:

$ grep -F "ab*c" <<< "ab*c"
ab*c

Answer 2

first of all, you should keep in mind: regex =/= glob

* has special meaning in regex. You have to escape it to match it literally. without escaping the *, grep tries to match ab+(any number of b)+c

for example:

abbbbbbbbbbbbc