|
|
expr help - managing strings
|
|
expr(1B) SunOS/BSD Compatibility Package Commands expr(1B) NAME
expr - evaluate arguments as a logical, arithmetic, or string expression SYNOPSIS
/usr/ucb/expr argument... DESCRIPTION
The expr utility evaluates expressions as specified by its arguments. After evaluation, the result is written on the standard output. Each token of the expression is a separate argument, so terms of the expression must be separated by blanks. Characters special to the shell must be escaped. Note: 0 is returned to indicate a zero value, rather than the null string. Strings containing blanks or other special characters should be quoted. Integer-valued arguments may be preceded by a unary minus sign. Internally, integers are treated as 32-bit, two's-complement numbers. The operators and keywords are listed below. Characters that need to be escaped are preceded by `'. The list is in order of increasing precedence, with equal precedence operators grouped within {} symbols. expr | expr Returns the evaluation of the first expr if it is neither NULL nor 0; otherwise, returns the evaluation of the second expr if it is not NULL; otherwise, 0. expr & expr Returns the first expr if neither expr is NULL or 0, otherwise returns 0. expr { =, , , <, <=, != } expr Returns the result of an integer comparison if both arguments are integers, otherwise returns the result of a lexical comparison. expr { +, - } expr Addition or subtraction of integer-valued arguments. expr { , /, % } expr Multiplication, division, or remainder of the integer-valued arguments. string : regular-expression match string regular-expression The two forms of the matching operator above are synonymous. The matching operators : and match compare the first argument with the second argument which must be a regular expression. Regular expression syntax is the same as that of regexp(5), except that all pat- terns are "anchored" (treated as if they begin with ^) and therefore ^ is not a special character, in that context. Normally, the matching operator returns the number of characters matched (0 on failure). Alternatively, the ... pattern symbols can be used to return a portion of the first argument. substr string integer-1 integer-2 Extracts the substring of string starting at position integer-1 and of length integer-2 characters. If integer-1 has a value greater than the length of string, expr returns a null string. If you try to extract more characters than there are in string, expr returns all the remaining characters from string. Beware of using negative values for either integer-1 or integer-2 as expr tends to run forever in these cases. index string character-list Reports the first position in string at which any one of the characters in character-list matches a character in string. length string Returns the length (that is, the number of characters) of string. ( expr ) Parentheses may be used for grouping. EXAMPLES
Example 1 Adding an integer to a shell variable Add 1 to the shell variable a. a='expr $a + 1' Example 2 Returning a path name segment Return the last segment of a path name (that is, the filename part). Watch out for / alone as an argument: expr will take it as the divi- sion operator (see BUGS below). # 'For $a equal to either "/usr/abc/file" or just "file"' expr $a : '.*/ $a Example 3 Using // characters to simplify the expression The addition of the // characters eliminates any ambiguity about the division operator and simplifies the whole expression. # A better representation of example 2. expr //$a : '.*/ Example 4 Returning the value of a variable Returns the number of characters in $VAR. expr $VAR : '.*' EXIT STATUS
expr returns the following exit codes: 0 If the expression is neither NULL nor 0. 1 If the expression is NULL or 0. 2 For invalid expressions. ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Availability |SUNWscpu | +-----------------------------+-----------------------------+ SEE ALSO
sh(1), test(1), attributes(5), regexp(5) DIAGNOSTICS
syntax error for operator/operand errors non-numeric argument if arithmetic is attempted on such a string division by zero if an attempt to divide by zero is made BUGS
After argument processing by the shell, expr cannot tell the difference between an operator and an operand except by the value. If $a is an =, the command: expr $a = '=' looks like: expr = = = as the arguments are passed to expr (and they will all be taken as the = operator). The following works: expr X$a = X= Note: the match, substr, length, and index operators cannot themselves be used as ordinary strings. That is, the expression: example% expr index expurgatorious length syntax error example% generates the `syntax error' message as shown instead of the value 1 as you might expect. SunOS 5.11 6 Jun 2000 expr(1B)
