Wildcards allow pattern matching within both Regular Expressions and in Globbing.
Bash performs filename expansion on unquoted command-line arguments.
Any command that uses quotes e.g. echo "hello" or echo '*' will echo the text.
Without quotes echo * will perform globbing and echo a list of files in the current directory.
Any character that appears in a pattern, other than the special pattern characters described below, matches itself.
The NUL character can not occur in a pattern. The special pattern characters must be quoted if they are to be matched literally.
The special pattern characters have the following meanings:
*Matches any string, including the null string.
?Matches any single character.
[...]Matches any one of the enclosed characters.A-C A pair of characters separated by a minus sign denotes a range; any character lexically between those two characters, inclusive, is matched.
To prevent any file named with dashes (-rf) being interpreted as a commnd option, it is a good idea to use /some/path/* (or ./* for the current directory) rather than just a bare *
If the first character following the `[' is a `!' or a `^' then any character not enclosed is matched. A '-' can be matched by including it as the first or last character in the set. A `]' can be matched by including it as the first character in the set. Within `[' and `]', character classes can be specified using the syntax [:class:], where class is one of the following classes defined in the POSIX 1003.2 standard:
alnum alpha ascii blank cntrl digit graph lower print punct space upper xdigit
A character class matches any character belonging to that class. Within `[' and `]', an equivalence class can be specified using the syntax [=c=], which matches all characters with the same collation weight (as defined by the current locale) as the character c. Within `[' and `]', the syntax [.symbol.] matches the collating symbol symbol.
If the extglob shell option is enabled using the shopt builtin, several extended pattern matching operators are recognized. In the following description, a pattern-list is a list of one or more patterns separated by a `|'. Composite patterns can be formed using one or more of the following sub-patterns:
?(pattern-list)Matches zero or one occurrence of the given patterns.
*(pattern-list)Matches zero or more occurrences of the given patterns.
+(pattern-list)Matches one or more occurrences of the given patterns.
@(pattern-list)Matches exactly one of the given patterns.
!(pattern-list)Matches anything except one of the given patterns.
How-to: Comparison Operators - exists, greater than, equal to.