Regular Expressions 101

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/
(\d+)(?=м\b|\s+метров)
/
iug
1st Capturing Group
(\d+)
\d
matches a digit zero through nine in any script except ideographic scripts (equivalent to \p{Nd})
+ matches the previous token between one and unlimited times, as many times as possible, giving back as needed (greedy)
Positive Lookahead
(?=м\b|\s+метров)
Assert that the Regex below matches
1st Alternative
м\b
м matches the character м with index 108410 (43C16 or 20748) literally (case insensitive)
\b assert position at a word boundary: (^\w|\w$|\W\w|\w\W)
2nd Alternative
\s+метров
\s
matches any kind of invisible character (equivalent to [\p{Z}\h\v])
+ matches the previous token between one and unlimited times, as many times as possible, giving back as needed (greedy)
метров
matches the characters метров literally (case insensitive)
Global pattern flags
i modifier: insensitive. Case insensitive match (ignores case of [a-zA-Z])
u modifier: unicode. Pattern strings are treated as UTF-16. Also causes escape sequences to match unicode characters
g modifier: global. All matches (don't return after first match)
Your regular expression does not match the subject string.Try launching the debugger to find out why.

Regular Expression
No Match

/
/
iug

Test String

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