MirBSD manpage: expr(1)
EXPR(1) BSD Reference Manual EXPR(1)
expr - evaluate expression
expr expression
The expr utility evaluates expression and writes the result on standard
output. All operators are separate arguments to the expr utility. Charac-
ters special to the command interpreter must be escaped.
Operators are listed below in order of increasing precedence. Operators
with equal precedence are grouped within { } symbols.
expr1 | expr2
Returns the evaluation of expr1 if it is neither an empty string
nor zero; otherwise, returns the evaluation of expr2.
expr1 & expr2
Returns the evaluation of expr1 if neither expression evaluates
to an empty string or zero; otherwise, returns zero.
expr1 {=, >, >=, <, <=, !=} expr2
Returns the results of integer comparison if both arguments are
integers; otherwise, returns the results of string comparison us-
ing the locale-specific collation sequence. The result of each
comparison is 1 if the specified relation is true, or 0 if the
relation is false.
expr1 {+, -} expr2
Returns the results of addition or subtraction of integer-valued
arguments.
expr1 {*, /, %} expr2
Returns the results of multiplication, integer division, or
remainder of integer-valued arguments.
expr1 : expr2
The ':' operator matches expr1 against expr2, which must be a
regular expression. The regular expression is anchored to the be-
ginning of the string with an implicit '^'.
If the match succeeds and the pattern contains at least one regu-
lar expression subexpression "\(...\)", the string corresponding
to "\1" is returned; otherwise, the matching operator returns the
number of characters matched. If the match fails and the pattern
contains a regular expression subexpression the null string is
returned; otherwise, returns 0.
Note: the empty string cannot be matched using
expr '' : '$'
This is because the returned number of matched characters (zero)
is indistinguishable from a failed match, so expr returns failure
(0). To match the empty string, use a structure such as:
expr X'' : 'X$'
Parentheses are used for grouping in the usual manner.
$ a=`expr $a + 1`
Add 1 to the variable a.
$ expr //$a : '.*/\(.*\)'
Return the filename portion of a pathname stored in variable a. The '//'
characters act to eliminate ambiguity with the division operator.
$ expr $a : '.*'
Return the number of characters in variable a.
The expr utility exits with one of the following values:
0 The expression is neither an empty string nor 0.
1 The expression is an empty string or 0.
2 The expression is invalid.
>2 An error occurred (such as memory allocation failure).
test(1)
The expr utility conforms to IEEE Std 1003.2 ("POSIX.2").
MirBSD #10-current July 3, 1993 1