Regex to validate the number of pipe delimited items

Question

Hi all,

I've got a string which is pipe '|' delimited. I need a regex to validate the number of items, based on the pipe character. So a regex which will do the following:

If the max number of items is three:

asdfasdf|asdfasdf|asdfasdf = VALID

asdfasdf|asdfasdf|asdfasdf|asdfasf = Not Valid

Also, this string may be empty.

Any help would be much appreciated

Regards

Answer 1

Are you using any programming language? If so, it probably has a specific functions for this. Using regex for everything string related is bad if it can be avoided.

PHP:

$items = explode('|', $mystr);
if ($items > $max) failed

Python:

items = mystr.split('|')
if len(items) > max: failed

Answer 2

^(?:[^|]+(?:\|[^|]+){0,2})?$

This will match an empty string or up to three pipe delimited items, where an item can be any character other than a pipe. Each item needs to be at least one character long in this pattern; if you want to allow for blank items, change the +s to *s.

If you want to change the upper limit of how many items are allowed, change {0,2} to {0,max-1}, where max is the limit you want (because you will have at most max - 1 pipes in your string for it to be valid).

Answer 3

It's probably easiest here to just count the | characters. E. g. in PowerShell:

PS> $valid = 'asdfasdf|asdfasdf|asdfasdf'
PS> $notvalid= 'asdfasdf|asdfasdf|asdfasdf|asdfasf'
PS> ($valid.ToCharArray() | where {$_ -eq '|' }).Count -lt 3
True
PS> ($notvalid.ToCharArray() | where {$_ -eq '|' }).Count -lt 3
False

Answer 4

^[^|]*(?:\|[^|]*){0,2}$

This assumes that the items between the pipes may be empty.

Answer 5

^([^|]*\|){0,2}[^|]*$

Allows empty string items, up to three items, change the 0 or 2 to alter the min/max range.

Answer 6

Why use a regular expression? Just iterate over the string and count each pipe. This is effectively doing what regex does, but without having to keep all of the pattern matching bookeeping.