```
Regex String	Description	Use Case	Explanation
^abc	Matches any string that starts with "abc"	To find lines in a text file that start with "abc"	^ asserts the start of a line, and abc is the literal string
abc$	Matches any string that ends with "abc"	To find lines in a text file that end with "abc"	abc is the literal string, and $ asserts the end of a line
a.b	Matches any string containing "a", any character, and then "b"	To find occurrences of "a" followed by any character and then "b"	a and b are literal characters, and . matches any character except a newline
\d{2,4}	Matches a sequence of 2 to 4 digits	To validate a year input with 2 to 4 digits	\d matches any digit, and {2,4} specifies a range of 2 to 4 occurrences
[A-Za-z]	Matches any single uppercase or lowercase letter	To find single letters in a text file	[A-Za-z] defines a character class containing all uppercase and lowercase letters
[^0-9]	Matches any character that is not a digit	To find non-digit characters in a text file	[^0-9] defines a character class with a negation (^) and a range for digits (0-9)
`(abc|def)`	Matches either "abc" or "def"	To find occurrences of either "abc" or "def" in a text file
a{3}	Matches exactly three consecutive "a" characters	To find occurrences of "aaa" in a text file	a is the literal character, and {3} specifies exactly 3 occurrences
\bword\b	Matches the word "word" as a whole word	To search for the whole word "word" in a text file	\b asserts a word boundary, and word is the literal string
(?i)abc	Matches "abc" case-insensitively	To find occurrences of "abc" regardless of case	(?i) sets the case-insensitive flag, and abc is the literal string
(\d+)\s+	Matches one or more digits followed by one or more whitespace characters	To find and separate numbers followed by spaces in a text file	(\d+) captures one or more digits, and \s+ matches one or more whitespace characters
(?<=@)\w+	Matches a word that follows the "@" symbol	To extract usernames from email addresses	(?<=@) is a positive lookbehind for the "@" symbol, and \w+ matches one or more word characters
```
Regex String	Description	Use Case	Explanation
^abc	Matches any string that starts with "abc"	To find lines in a text file that start with "abc"	^ asserts the start of a line, and abc is the literal string
abc$	Matches any string that ends with "abc"	To find lines in a text file that end with "abc"	abc is the literal string, and $ asserts the end of a line
a.b	Matches any string containing "a", any character, and then "b"	To find occurrences of "a" followed by any character and then "b"	a and b are literal characters, and . matches any character except a newline
\d{2,4}	Matches a sequence of 2 to 4 digits	To validate a year input with 2 to 4 digits	\d matches any digit, and {2,4} specifies a range of 2 to 4 occurrences
[A-Za-z]	Matches any single uppercase or lowercase letter	To find single letters in a text file	[A-Za-z] defines a character class containing all uppercase and lowercase letters
[^0-9]	Matches any character that is not a digit	To find non-digit characters in a text file	[^0-9] defines a character class with a negation (^) and a range for digits (0-9)
`(abc|def)`	Matches either "abc" or "def"	To find occurrences of either "abc" or "def" in a text file
a{3}	Matches exactly three consecutive "a" characters	To find occurrences of "aaa" in a text file	a is the literal character, and {3} specifies exactly 3 occurrences
\bword\b	Matches the word "word" as a whole word	To search for the whole word "word" in a text file	\b asserts a word boundary, and word is the literal string
(?i)abc	Matches "abc" case-insensitively	To find occurrences of "abc" regardless of case	(?i) sets the case-insensitive flag, and abc is the literal string
(\d+)\s+	Matches one or more digits followed by one or more whitespace characters	To find and separate numbers followed by spaces in a text file	(\d+) captures one or more digits, and \s+ matches one or more whitespace characters
(?<=@)\w+	Matches a word that follows the "@" symbol	To extract usernames from email addresses	(?<=@) is a positive lookbehind for the "@" symbol, and \w+ matches one or more word characters