Regular Expressions 101

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/
\bcountr(y|ies)\b
/
gmi
\b assert position at a word boundary: (^\w|\w$|\W\w|\w\W)
countr
matches the characters countr literally (case insensitive)
1st Capturing Group
(y|ies)
1st Alternative
y
y matches the character y with index 12110 (7916 or 1718) literally (case insensitive)
2nd Alternative
ies
ies
matches the characters ies literally (case insensitive)
\b assert position at a word boundary: (^\w|\w$|\W\w|\w\W)
Global pattern flags
g modifier: global. All matches (don't return after first match)
m modifier: multi line. Causes ^ and $ to match the begin/end of each line (not only begin/end of string)
i modifier: insensitive. Case insensitive match (ignores case of [a-zA-Z])
Your regular expression does not match the subject string.Try launching the debugger to find out why.

Regular Expression
No Match

/
/
gmi

Test String