Basic Regular Expressions (BRE)

Metachar .

Matches any single character.

Example:

x.z matches "xyz", etc., but within bracket expressions, the dot character matches a literal dot, e.g., [x.y] matches only "x", ".", or "y"

Metachar [ ]

Matches a single character that is contained within the brackets.

Example:

[xyz] matches "x", "y", or "z", where [a-z] specifies a range which matches any lowercase letter from "a" to "z". Note that the - character is treated as a literal character if it is the last or the first e.g., [-xyz]

Metachar [^ ]

Matches a single character that is not contained within the brackets.

Example:

[^xyz] matches any character other than "x", "y", or "z".

Metachar ^

Matches the starting position within the string.

Example:

^[xterm] matches any string that starts with xterm.

Metachar $

Matches the ending position of the string or the position just before a string-ending newline.

Example:

[mb]at$ matches "mat" and "bat", but only at the end of the string or line.

Metachar ( )

The string matched within the parentheses can be recalled later, also called a block or capturing group.

Example:

([0-9]+)([a-z]+) the first group matches atleast one digit and the second group atleast one alphabet.

Metachar *

Matches the preceding element zero or more times.

Example:

xy*z matches "xy", "xyz", "xyyz", etc.

Metachar {m,n}

Matches the preceding element at least m and not more than n times.

Example:

Y{2,3} matches only "YY", "YYY".