Regular Expressions 101

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/
^\d{0,5}\s\-\s\d{0,2}\/\d{0,2}\/\d{4}$
/
gm
^ asserts position at start of a line
\d
matches a digit (equivalent to [0-9])
{0,5} matches the previous token between 0 and 5 times, as many times as possible, giving back as needed (greedy)
\s matches any whitespace character (equivalent to [\r\n\t\f\v ])
\- matches the character - with index 4510 (2D16 or 558) literally (case sensitive)
\s matches any whitespace character (equivalent to [\r\n\t\f\v ])
\d
matches a digit (equivalent to [0-9])
{0,2} matches the previous token between 0 and 2 times, as many times as possible, giving back as needed (greedy)
\/ matches the character / with index 4710 (2F16 or 578) literally (case sensitive)
\d
matches a digit (equivalent to [0-9])
{0,2} matches the previous token between 0 and 2 times, as many times as possible, giving back as needed (greedy)
\/ matches the character / with index 4710 (2F16 or 578) literally (case sensitive)
\d
matches a digit (equivalent to [0-9])
{4} matches the previous token exactly 4 times
$ asserts position at the end of a line
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)
Your regular expression does not match the subject string.Try launching the debugger to find out why.

Regular Expression
No Match

/
/
gm

Test String