Reg ex find and replace with groups

Question

I'm trying to find the screen names in each line of text eg. screen_name: CoinLibre2009. After finding every screen name I have to replace each screen name with the original first character then exactly four asterisks (****) and then the last character. For example the screen name CoinLibre2009 would become C****9. I'm thinking that I need to use groups and that I should include the "screen_name: " in my find, and just include it back in with the replace.

Here are a few lines of the text I'm working with:

posted: Sat Feb 03 2018 11:03:09    text: Today we can see positive trends for growth, but will there be a new fall? crypto screen_name: Ksandimo   location: null  verified: false followers_count: 1597   friends_count: 17   lang: ru    retweet_count: 0    favorite_count: 0
posted: Sat Feb 03 2018 11:03:14    text: 8745.02$ per now  screen_name: CoinLibre2009  location: Free World    verified: false followers_count: 113    friends_count: 110  lang: ru    retweet_count: 0    favorite_count: 0
posted: Sat Feb 03 2018 11:03:16    text: Current price of is $8745.02  screen_name: bitcoinavg location: null  verified: false followers_count: 44 friends_count: 9    lang: en    retweet_count: 0    favorite_count: 0
posted: Sat Feb 03 2018 11:03:25    text: Think weve hit resistance for Bitcoin now. Will it fully recover? Im not sure screen_name: jasongaved location: Brighton & Hove / London  verified: false followers_count: 1996   friends_count: 1967 lang: en    retweet_count: 0    favorite_count: 0
posted: Sat Feb 03 2018 11:03:28    text: Today's price is $8745.02 as of February 3, 2018 at 11:59AM   screen_name: FR33Q  location: Europe    verified: false followers_count: 1164   friends_count: 1998 lang: en    retweet_count: 0    favorite_count: 0

Also here is a screenshot of what the data looks like in notepad ++:

I'm using reg ex in Notepad++ for this task. Here is what I have come up with so far. screen_name:\\s[A-Za-z0-9]+ Then this is where I get stuck, as I'm not sure how to replace the first and last characters.

Answer 1

You can use capturing groups in the regex pattern and replacement back references (also called placeholders) in the replacement pattern. Besides, if you want to match letters, digits and underscores , use \\w instead of a custom [a-zA-Z0-9] .

Use

(screen_name:\s\w)\w*(\w)

The (screen_name:\\s\\w) captures the screen_name: and a whitespace into Group 1 later referred to as $1 from the replacement pattern, \\w* just matches 0+ word chars and then (\\w) matches and captures a single word char into Group 2 later referred to as $2 from the replacement pattern.

Replace with $1****$2 .

See the regex demo .

Answer 2

(screen_name:\s[A-Za-z0-9_])[A-Za-z0-9_]*([A-Za-z0-9_]) => $1****$2