How to use regular expression to search for set of characters in a given string from right to left until we find first space.

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I have below string :
"ISOC Charges: Member 716 - LGIM_GASPEN_MG"

My requirement is to search set of characters in above string from right to left until we find first space. So, I should get the value = "LGIM_GASPEN_MG"

What I have tried:

I tried using regular expression but not getting how to traverse the string from right to left.

Posted 28-Dec-21 19:33pm

Member 9346617

Updated 28-Dec-21 21:02pm

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Peter_in_2780 29-Dec-21 2:00am

Regex is the wrong tool for that job. Many languages include a "LastIndexOf()" or similar function. If your language of choice doesn't it's dead easy to roll your own. There is a simple regex to do what you want, but as I said, it's the wrong way to attack this problem.

2 solutions

Solution 1

You don't: regexes don;t work that way.
You can however trigger on the last space:

(?:\s)[^\s]+$

For an explanation of that, get a copy of Expresso[^] - it's free, and it examines, tests, and generates Regular expressions.

Posted 28-Dec-21 20:02pm

OriginalGriff

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Patrice T · Accepted Answer · 2021-12-28T21:02:00

Quote:
My requirement is to search set of characters in above string from right to left until we find first space. So, I should get the value = "LGIM_GASPEN_MG"

Since RE works left to right, you need to look at last space and skip anything before that last space.
This RE find last group of letters in string:

\w+$

Just a few interesting links to help building and debugging RegEx.
Here is a link to RegEx documentation:
perlre - perldoc.perl.org[^]
Here is links to tools to help build RegEx and debug them:
.NET Regex Tester - Regex Storm[^]
Expresso Regular Expression Tool[^]
RegExr: Learn, Build, & Test RegEx[^]
Online regex tester and debugger: PHP, PCRE, Python, Golang and JavaScript[^]
This one show you the RegEx as a nice graph which is really helpful to understand what is doing a RegEx: Debuggex: Online visual regex tester. JavaScript, Python, and PCRE.[^]
This site also show the Regex in a nice graph but can't test what match the RegEx: Regexper[^]