Some Definitions:
Literal:
Any Character used in a search or matching expressions.
Metacharacter:
One or more special characters that have a unique meaning and are not used as literals.
Target String:
The string that we will be searching.
Search Expression:
The expression that we will be using to search our target string.
Meta Characters:
- “[ ]” – Match anything inside the square brackets for one character position once and only once. Eg: [12] searches 1 and 2.
- “-“ - Range Sperator. Allows us to define a range. Eg: [0-9] searches 0 to 9.
- “^” – Negates the expression. [^Ff] searches anything except upper/lower case F. And also it looks at the beginning of the word. I.e. “^Hai” looks at the beginning of the word Hai
- “$” - Looks at the end of the Target String.
- “.” - Any character in this position. Eg: “ton.” Searches and finds “tons” and "tonneau” and not the “wanton”.
Iteration Metacharacters:
Quantifiers that can control the number of times a character or string is found in our searches.
- “?” – Matches the preceding character 0 or 1 time only. Eg: “Colou?r” will find both “Colors” and “Colours”
- “*” – Matches the preceding character 0 or more times. Eg: “tre*” will find “tree” and “tread”.
- “+” – Matches the previous character 1 or more times exactly.
- “{n}” – Matches the preceding character n times exactly. Eg: For searching phone no. we can as “[0-9]{3} – [0-9] {4}” which will find as 123 – 4567.
- “{n,m}” – Matches the preceding character atleast n times but not more than m times. Eg: “ba{2,3}b” will find “baab” and “baaab” but not “bab” or “baaaab”.
Other Metacharacters:
§ “()” – Used to group parts of our search expression together.
§ “|” – Alteration in techspeak means find the left hand or right hand values. Eg: “gra(a|e)y” will find “gray” or “grey”
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