(period) Matches any single character except a newline. Remember that spaces are treated as characters.

Matches zero or more (as many as there are) of the single character that immediately precedes it.

The * can follow a metacharacter, such as ., or a range in brackets.

When used at the start of a regular expression, ^ requires that the following regular expression be found at the beginning of the line. When not at the beginning of a regular expression, ^ stands for itself.

When used at the end of a regular expression, $ requires that the preceding regular expression be found at the end of the line. When not at the end of a regular expression, $ stands for itself.

Treats the following special character as an ordinary character. Use \ to get a literal backslash.

Matches whatever regular expression was used in the last search.

Matches any one of the characters enclosed between the brackets. A range of consecutive characters can be specified by separating the first and last characters in the range with a hyphen.

You can include more than one range inside brackets and specify a mix of ranges and separate characters.

Most metacharacters lose their special meaning inside brackets, so you don’t need to escape them if you want to use them as ordinary characters. Within brackets, the three metacharacters you still need to escape are - ]. The hyphen (-) acquires meaning as a range specifier; to use an actual hyphen, you can also place it as the first character inside the brackets.

A caret (^) has special meaning only when it’s the first character inside the brackets, but in this case, the meaning differs from that of the normal ^ metacharacter. As the first character within brackets, a ^ reverses their sense: the brackets match any one character not in the list. For example, [^a-z] matches any character that’s not a lowercase letter.

Saves the pattern enclosed between ( and ) into a special holding space or “hold buffer.” You can save up to nine patterns in this way on a single line.

You can also use the n notation within a search or substitute string:

:s/(abcd)1/alphabet-soup/

changes abcdabcd into alphabet-soup.^[3]

Matches characters at the beginning (<) or end (>) of a word. The end or beginning of a word is determined either by a punctuation mark or by a space. Unlike (...), these don’t have to be used in matched pairs.

A POSIX character class consists of keywords bracketed by [: and :]. The keywords describe different classes of characters, such as alphabetic characters, control characters, and so on (see the following table).

A collating symbol is a multicharacter sequence that should be treated as a unit. It consists of the characters bracketed by [. and .].

An equivalence class lists a set of characters that should be considered equivalent, such as e and è. It consists of a named element from the locale, bracketed by [= and =].

Is replaced with the text matched by the nth pattern previously saved by ( and ), where n is a number from one to nine, and previously saved patterns (kept in hold buffers) are counted from the left on the line.

Treats the following special character as an ordinary character. To specify a real backslash, type two in a row (\).

Is replaced with the entire text matched by the search pattern when used in a replacement string. This is useful when you want to avoid retyping text.

The string found is replaced with the replacement text specified in the last substitute command. This is useful for repeating an edit.

Changes the next character in the replacement string to uppercase or lowercase, respectively.

U and L are similar to u or l, but all following characters are converted to uppercase or lowercase until the end of the replacement string or until e or E is reached. If there is no e or E, all characters of the replacement text are affected by the U or L.