Comprehensive and Detailed In-Depth Explanation:
The regular expression100.$can be broken down as follows:
100:Matches the exact sequence of digits "100".
(dot): Representsany single character.
$:Indicates theend of the line.
Therefore, the pattern100.$matches anyfour-character sequencethat starts with "100" and ends withany single character.
1000 (A): Matches because it has four digits, starting with "100" and ending with "0".
1001 (B): Matches because it has four digits, starting with "100" and ending with "1".
10000 (C): Doesnot matchbecause it hasfive digits.
100 (D): Doesnot matchbecause it only hasthree digits.
[Reference:, Huawei Regular Expression Configuration Guide, Networking Regex Matching Principles, ===========, ]
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