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Ordinary characters consist of all printable and non-printable characters that are not explicitly designated as metacharacters. This includes all uppercase and lowercase alphabetic characters, all digits, all punctuation marks, and some symbols.
The simplest form of a regular expression is a single, ordinary character that matches itself in a searched string. For example, a single-character pattern, such as A, matches the letter A wherever it appears in the searched string. Here are some examples of single-character regular expression patterns:
/a/ /7/ /M/
You can combine a number of single characters to form a large expression. For example, the following regular expression combines the single-character expressions: a, 7, and M.
Notice that there is no concatenation operator. You just type one character after another.