picoCTF Match The Regex writeup

This is an easy web challenge.

This websites asks for an input from the user

I tried 'hello' and it alerted me with a 'wrong message' alert.

Then I went to check the source code of the website by Right-click -> View Page Source, scrolled to the bottom and found the script that the website was running:

We see the regex pattern ^p.....F!? in the comment.

The regex pattern ^p.....F!? matches strings that start with a lowercase "p", followed by exactly five characters of any kind, then an uppercase "F", and optionally ending with an exclamation mark.

The ^ asserts the start of the string, while the . wildcard matches any single character except newline.

The !? means that the exclamation mark at the end is optional — the string may or may not include it.

My immediate guess was trying to input picoCTF:

... and that's how I got the flag to solve this challenge.