Regular Expressions 101

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/
.Disconnected from (invalid |authenticating )?user . [^ ] port [0-9]( \[preauth\])?$
/
gm
.
matches any character (except for line terminators)
* matches the previous token between zero and unlimited times, as many times as possible, giving back as needed (greedy)
Disconnected from matches the characters Disconnected from literally (case sensitive)
1st Capturing Group
(invalid |authenticating )?
? matches the previous token between zero and one times, as many times as possible, giving back as needed (greedy)
1st Alternative
invalid
invalid matches the characters invalid literally (case sensitive)
2nd Alternative
authenticating
authenticating matches the characters authenticating literally (case sensitive)
user matches the characters user literally (case sensitive)
.
matches any character (except for line terminators)
* matches the previous token between zero and unlimited times, as many times as possible, giving back as needed (greedy)
matches the character literally (case sensitive)
Match a single character not present in the list below
[^ ]
+ matches the previous token between one and unlimited times, as many times as possible, giving back as needed (greedy)
matches the character literally (case sensitive)
port matches the characters port literally (case sensitive)
Match a single character present in the list below
[0-9]
+ matches the previous token between one and unlimited times, as many times as possible, giving back as needed (greedy)
0-9 matches a single character in the range between 0 (index 48) and 9 (index 57) (case sensitive)
2nd Capturing Group
( \[preauth\])?
$ 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