Text file search for match strings regex

Question

I am trying to understand how regex works and what are the possibilities of working with it. So I have a txt file and I am trying to search for 8 char long strings containing numbers. for now I use a quite simple option:

clear
Get-ChildItem random.txt | Select-String -Pattern [0-9][a-z] | foreach {$_.line}

It sort of works but I am trying to find a better option. ATM it takes too long to read through the left out text since it writes entire lines and it does not filter them by length.

It would help for us to see an example of the input you have, and an example of what you would like it to look like - anonymized/cleaned of any real-world data, of course. — gravity, Mar 29 '16 at 15:12
If you have HTML input you [shouldn't use regular expressions in the first place](http://stackoverflow.com/a/1732454/1630171). — Ansgar Wiechers, Mar 29 '16 at 15:27
@AnsgarWiechers well i have truly enjoyed this comparison "While it is true that asking regexes to parse arbitrary HTML is like asking Paris Hilton to write an operating system" — tuarianking, Mar 29 '16 at 15:34

Mathias R. Jessen · Accepted Answer · 2016-03-29T15:21:04.573

2

You can use a lookahead to assert that a string contains at least 1 digit, then specify the length of the match and finally anchor it with ^ (start of string) and $ (end of string) if the string is on a line of its own, or \b (word boundary) if it's part of an HTML document as your comments seem to suggest:

Get-ChildItem C:\files\ |Select-String -Pattern '^(?=.*\d)\w{8}$'
Get-ChildItem C:\files\ |Select-String -Pattern '\b(?=.*\d)\w{8}\b'

edited Mar 29 '16 at 15:21

answered Mar 29 '16 at 15:16

Mathias R. Jessen

157,619
12
148
206

i would have suggested http://regexone.com/ for a tutorial instead. can do it within the browser with inline validation. – Hazonko Mar 29 '16 at 15:17
hi, thanks for the answer i made a bit of an update in the comments :) will try thanks – tuarianking Mar 29 '16 at 15:20
thanks for the update :) should be output be done like i did previously in this case? – tuarianking Mar 29 '16 at 15:24
If you want the match, rather than the full string, you should look at `$_.Matches` instead of `$_.Line` – Mathias R. Jessen Mar 29 '16 at 15:34
@Hazonko You're more than welcome to update my post with a link to a better learning resource for lookaheads if you feel so inclined :) – Mathias R. Jessen Mar 29 '16 at 15:41
@MathiasR.Jessen well thanks that helps a lot i just write it like this get-childitem | select-string -pattern [0-9][0-9a-z][0-9a-z][0-9a-z][0-9a-z][0-9a-z][0-9a-z][0-9a-z][<]| foreach {$_.Matches} – tuarianking Mar 29 '16 at 15:43

score 1 · Answer 2 · answered Mar 29 '16 at 15:15

The pattern [0-9][a-z] matches a digit followed by a letter. If you want to match a sequence of 8 characters use .{8}. The dot in regular expressions matches any character except newlines. A number in curly brackets matches the preceding expression the given number of times.

If you want to match non-whitespace characters use \S instead of .. If you want to match only digits and letters use [0-9a-z] (a character class) instead of ..

For a more thorough introduction please go find a tutorial. The subject is way too complex to be covered by a single answer on SO.

hi, thanks for the answer i made a bit of an update in the comments :) will try thanks — tuarianking, Mar 29 '16 at 15:20

Hazonko · Answer 3 · 2016-03-29T15:20:33.837

0

What you're currently searching for is a single number ranging from 0-9 followed by a single lowercase letter ranging from a-z.

this, for example, will match any 8 char long strings containing only alphanumeric characters.

\w{8}

i often forget what some regex classes are, and it may be useful to you as a learning tool, but i use this as a point of reference: http://regexr.com/

It can also validate what you're typing inline via a text field so you can see if what you're doing works or not.

If you need more of a tutorial than a reference, i found this extremely useful when i learned: regexone.com

edited Mar 29 '16 at 15:20

answered Mar 29 '16 at 15:15

Hazonko

1,025
1
15
30

@tuarianking using your example in your comment above, it does match to what you're trying to get. – Hazonko Mar 29 '16 at 15:23

Text file search for match strings regex

3 Answers3