Tryhackme – Regular expressions

In this walk through, we will be going through the Regular expressions room from Tryhackme. This room will teach us about the basics of regular expressions or regex and how to use them. On that note, let’s get started.

Task 1 – Introduction

Task 2 – Charsets

Question 1 – Match all of the following characters: c, o, g

[cog]

Question 2 – Match all of the following words: cat, fat, hat

[cfh]at

Question 3 – Match all of the following words: Cat, cat, Hat, hat

[CcHh]at

Question 4 – Match all of the following filenames: File1, File2, file3, file4, file5, File7, file9

[Ff]ile[1-9]

Question 5 – Match all of the filenames of question 4, except “File7” (use the hat symbol)

[Ff]ile[^7]

Task 3 – Wildcards and optional characters

Question 1 – Match all of the following words: Cat, fat, hat, rat

 .at

Question 2 – Match all of the following words: Cat, cats

[Cc]ats?

Question 3 – Match the following domain name: cat.xyz

cat\.xyz

Question 4 – Match all of the following domain names: cat.xyz, cats.xyz, hats.xyz

[ch]ats?\.xyz

Question 5 – Match every 4-letter string that doesn’t end in any letter from n to z

 ...[^n-z]

Question 6 – Match bat, bats, hat, hats, but not rat or rats (use the hat symbol)

[^r]ats?

Task 4 – Metacharacters and repetitions

Question 1 – Match the following word: catssss

cats{4}

Question 2 – Match all of the following words (use the * sign): Cat, cats, catsss

[Cc]ats*

Question 3 – Match all of the following sentences (use the + sign): regex go br, regex go brrrrrr

regex go br+

Question 4 – Match all of the following filenames: ab0001, bb0000, abc1000, cba0110, c0000 (don’t use a metacharacter)

[abc]{1,3}[01]{4}

Question 5 – Match all of the following filenames: File01, File2, file12, File20, File99

[Ff]ile\d{1,2}

Question 6 – Match all of the following folder names: kali tools, kali     tools

kali\s+tools

Question 7 – Match all of the following filenames: notes~, stuff@, gtfob#, lmaoo!

\w{5}\W

Question 8 – Match the string in quotes (use the * sign and the \s, \S metacharacters): “2f0h@f0j0%!     a)K!F49h!FFOK”

\S*\s*\S*

Question 9 – Match every 9-character string (with letters, numbers, and symbols) that doesn’t end in a “!” sign

\S{8}[^!]

Question 10 – Match all of these filenames (use the + symbol): .bash_rc, .unnecessarily_long_filename, and note1

 \.?\w+

Task 5 – Starts with/ ends with, groups, and either/ or

Question 1 – Match every string that starts with “Password:” followed by any 10 characters excluding “0”

 ^Password:[^0]{10}

Question 2 – Match “username: ” in the beginning of a line (note the space!)

^username:\s

Question 3 – Match every line that doesn’t start with a digit (use a metacharacter)

^\D

Question 4 – Match this string at the end of a line: EOF$

EOF\$$

Question 5 – Match all of the following sentences:

• I use nano
• I use vim

i use (nano|vim)

Question 6 – Match all lines that start with $, followed by any single digit, followed by $, followed by one or more non-whitespace characters

\$\d\$\S+

Question 7 – Match every possible IPv4 IP address (use metacharacters and groups)

(\d{1,3}\.){3}\d{1,3}

Question 8 – Match all of these emails while also adding the username and the domain name (not the TLD) in separate groups (use \w): [email protected], [email protected], [email protected]

 c

Task 6 – Conclusion

Also Read: Tryhackme – Red Team Fundamentals

So that was “Regular expressions” for you. In this room, we have learned about the basics of regular expressions or regex and how to use them. We have covered the usage of basic charsets and wildcard characters. Along with the usage of Metacharacters, repetition, start and ends with. On that note, i will take your leave and meet you in the next one. So stay tuned and till then, “Hack the planet”.