Grep with regular expressions
bash, grep, linux, regex
Solution
You're thinking of a shell wildcard, where `*` matches anything. In regular expressions, a `*` is a quantifier that means "zero or more" of whatever immediately precedes it, which in this case is `3`.
So your expression means `113` followed by zero or more `3`s.
Problem
Consider this text file: ``` TEST FILE : test #No match #No match Run grep "1133*" on this file #Match #No match This line contains the number 113. #Match This line contains the number 13. #No match This line contains the number 133. #No match This line contains the number 1133. #Match This line contains the number 113312. #Match This line contains the number 1112. #No match This line contains the number 113312312. #Match This line contains no numbers at all. #No match ``` How does the `grep` command evaluate the `1133*` regular expression? ``` echo "Consider this text file: TEST FILE : test #No match #No match Run grep \"1133*\" on this file #Match #No match This line contains the number 113. #Match This line contains the number 13. #No match This line contains the number 133. #No match This line contains the number 1133. #Match This line contains the number 113312. #Match This line contains the number 1112. #No match This line contains the number 113312312. #Match This line contains no numbers at all. #No match" | grep "1133*" ``` Outputs: ``` Run grep "1133*" on this file #Match This line contains the number 113. #Match This line contains the number 1133. #Match This line contains the number 113312. #Match This line contains the number 113312312. #Match ``` Why is the line containing `113` a positive? Is the regular expression `1133*` meant to mean anything else than find all lines that contain the word `1133+anything else`? This example was found on the tldp regexp documentation page.