expr supports pattern matching and other string operators. These
have higher precedence than both the numeric and relational operators (in
the next sections).
Perform pattern matching. The arguments are converted to strings and the
second is considered to be a (basic, a la GNU
expression, with a
^ implicitly prepended. The first argument is
then matched against this regular expression.
If the match succeeds and regex uses ‘\(’ and ‘\)’, the
: expression returns the part of string that matched the
subexpression; otherwise, it returns the number of characters matched.
If the match fails, the
: operator returns the null string if
‘\(’ and ‘\)’ are used in regex, otherwise 0.
Only the first ‘\( … \)’ pair is relevant to the return value; additional pairs are meaningful only for grouping the regular expression operators.
In the regular expression,
operators which respectively match one or more, zero or one, or separate
alternatives. SunOS and other
expr’s treat these as regular
characters. (POSIX allows either behavior.)
See Regular Expression Library in Regex, for details of
regular expression syntax. Some examples are in Examples of expr.
An alternative way to do pattern matching. This is the same as ‘string : regex’.
Returns the substring of string beginning at position with length at most length. If either position or length is negative, zero, or non-numeric, returns the null string.
Returns the first position in string where the first character in charset was found. If no character in charset is found in string, return 0.
Returns the length of string.
Interpret token as a string, even if it is a keyword like match
or an operator like
This makes it possible to test
expr length + "$x" or
expr + "$x" : '.*/\(.\)' and have it do the right thing even if
the value of $x happens to be (for example)
This operator is a GNU extension. Portable shell scripts should use
" $token" : ' \(.*\)' instead of
expr interpret keywords as strings, you must use the