Using regex to match beginning and end of string [Java]

Question

I have a list of files in a folder:

maze1.in.txt
maze2.in.txt
maze3.in.txt

I've used substring to remove the .txt extensions. How do I use regex to match the front and the back of the file name? I need it to match "maze" at the front and ".in" at the back, and the middle must be a digit (can be single or double digit).

I've tried the following

if (name.matches("name\\din")) {
    //dosomething
}

It doesn't match anything. What is the correct regex expression to use?

Answer 1

I'm a little confused what you are asking for in particular

    ^(maze[0-9]*\.in)$

This will match maze(any number).in

 ^(maze[0-9]*\.in)\.txt$

this will match maze(any number).in.txt -- excludes the .txt NO NEED FOR USING SUB STRING!

Edit live on Debuggex

The think i would be wary about as of right now is the capture groups ... I'm not particularly sure what you are doing with this regex. However, I believe explaining capture groups could benefit you.

A capture group for instance is denoted by () this is basically store them in the pattern array and is a way to parse stuff.

example maze1.in.txt

So if you want to capture the entire line minus .txt i would use this ^(maze[0-9]*\\.in\\.txt)$

However, if I wanted to capture things separately I would do this ^(maze)([0-9]*)(\\.in)\\.txt$ this will exclude .txt but include maze, the number, and .in IN separate indexes of the pattern array.

Answer 2

You need regex anchors that tell the regex to

start at the beginning: ^

and signal the end of the string: $

^maze[\d]{0,2}\.in$

or in Java:

name.matches("^maze[\\d]{0,2}\\.in$");

Also, your regex wasn't matching strings with a dot ( . ) which would not accept your examples given. You need to add \\. to the regex to accept dots because . is a special character.

Answer 3

Your original solution doesn't work because string "name" is not in your text. It is "maze".
You can try this

name.matches("maze\\d{1,2}\\.in")

d{1,2} is used to match a digit(can be single or double digit).

Answer 4

It is always good to think of what you are trying to do in english, before you create regular expressions.

You want to match a word maze followed by a digit, followed by a literal period . followed by another word.

word   `\w` matches a word character
digit  `\d` matches a single digit
period `\.` matches a literal period
word   `\w` matches a word character

putting it all together into a single string you get (keep in mind the double backslash for the Java escape and the pluses to repeat the previous match one or more times):

"\\w+\\d\\.\\w+"

The above is the generic case for any file name in the format xxx1.yyy , if you wanted to match maze and in specifically, you can just add those in as literal strings.

"maze\\d+\\.in"

example: http://ideone.com/rS7tw1

Answer 5

name.matches("^maze[0-9]+\\.in\\.txt$")