How to allow spaces in the beginning of each row using regex?

Question

I currently have a validation expression that almost works the way I want it to, only I am having trouble allowing spaces at the beginning of some rows. I'd like to support unlimited spaces at the beginning of rows.

Here is an example and the expression that I am having trouble with: ^(?=.?[ \t]([., \t]))(?:[1-9][0-9](?:[ \t]\1[ \t][1-9][0-9])+[ \t]*\r?\n?)+$

Here is the example string I'd like to match:

10 11 12 13 14 30
 9 41 42 44 46 48
10 11 12 13 14 30

My first question which explains what I want to do specifically is found: here

Could you add to your question an example string you would like to match? — Wilder Pereira, Aug 10 '17 at 02:18
Will your input only be a string with number and spaces? Your regex seems to be too complex for that. — Wilder Pereira, Aug 10 '17 at 02:20
No, I will accept multiple delimiter types: commas, spaces, tabs. — justinpees, Aug 10 '17 at 02:21
Your regex doesn't make sense. Maybe if you explain in detail what you are trying to do. And especially why the `\1` backreference was used... — , Aug 10 '17 at 02:22
So I take it you are trying to validate the entire string all at once using a single delimiter ? Using a lookahead to find the delimiter will always return the same result because it is atomic and won't backtrack. — , Aug 10 '17 at 02:24
@sln Yes, and I'd like to allow spaces at the beginning of rows. I'd like to keep the rest of my expression as is if possible. — justinpees, Aug 10 '17 at 02:27
@sln \s doesn't work, that's for sure. What do you think is causing the problem? — justinpees, Aug 10 '17 at 02:30
I know what the problem is. The solution depends on having more than 1 item on each line. Is that going to be the case? — , Aug 10 '17 at 02:32
@sln can it be fixed if I use only 0-9? There will always be more than one number in each row if that's what you were asking. — justinpees, Aug 10 '17 at 02:33
@sln Yes there will always be more than one item on each line. — justinpees, Aug 10 '17 at 02:52

score 2 · Accepted Answer · answered Aug 10 '17 at 03:01

2

As an advanced topic, this will be a little difficult to understand, but here goes.

^\s*[1-9][0-9]*\s*(?=([., \t]))(?:\s*(?:\1|\r?\n)\s*[1-9][0-9]*)+\s*$

You have a unique problem since you are trying to validate all the rows
as a single string.
The problem comes when the delimiter is not available at the end of
a row.

To get around that, use an alternation with the backreference (delimiter)
or a line break.

As for whitespace at the beginning of string, just intersperse with \s.

See here https://regex101.com/r/nir0uI/1 and here https://regex101.com/r/nir0uI/2

Formatted

 ^ 
 \s* 
 [1-9] [0-9]* 
 \s* 
 (?=                                # Lookahead for delimiter.
      ( [., \t] )                   # (1)
 )
 (?:
      \s* 
      (?: \1 | \r? \n )
      \s*       
      [1-9] [0-9]* 
 )+
 \s*  
 $

answered Aug 10 '17 at 03:01

Wow a true genius thanks so much!!! Will I run into any problems using tabs as delimiters with this solution? – justinpees Aug 10 '17 at 03:06
Also, would it be hard to accept the delimiter at the end of each line? I see that spaces can be added to the end of each line so I pressure that tabs would also work. But how about a single comma (or space-comma) and dot (or space-dot) at the end of each line? depending on which delimiter is used. I know this could be complicating things much more. Tell me if it's too much. – justinpees Aug 10 '17 at 03:13
1

@justinpees - The regex101 links show the delimiter (group 1) in green highlight. The way it is now, there are 3 conditions around the line break (\r?\n). `No delimiter` or `Delimiter-line break` or `Line break-delimiter`. See https://regex101.com/r/Vll1fT/1. If you want to change one of those conditions, let me know. – Aug 10 '17 at 12:38
thanks again so much, I think I had another question. I'll send out a comment soon when I remember what it was. – justinpees Aug 10 '17 at 15:20
do you know if it's possible to make a ValidationExpression like this for when I ask users to upload a .txt file? I'd like to validate the content inside the uploaded .txt file. I will make a new question for this. I'd like to know if it's possible first. – justinpees Aug 10 '17 at 16:39

score 1 · Answer 2 · answered Aug 10 '17 at 02:15

1

\s

might help at the beginning of your expression.

answered Aug 10 '17 at 02:15

botjaeger

93
8

I tried that, it doesn't seem to work. You can test it yourself. Is it because I have space set as a delimiter? – justinpees Aug 10 '17 at 02:17
What exactly are you trying to validate? – botjaeger Aug 10 '17 at 02:17

score 1 · Answer 3 · answered Aug 10 '17 at 02:23

1

Add zero or more whitespace to the front of your regex:

^\s*<your regex here>

answered Aug 10 '17 at 02:23

Bohemian

412,405
93
575
722

How to allow spaces in the beginning of each row using regex?

3 Answers3