EXPR(1)EXPR(1)NAMEexpr - evaluate arguments as an expression
SYNOPSISexpr arg ...
DESCRIPTION
The arguments are taken as an expression. After evaluation, the result
is written on the standard output. Each token of the expression is a
separate argument.
The operators and keywords are listed below. The list is in order of
increasing precedence, with equal precedence operators grouped.
expr | expr
yields the first expr if it is neither null nor `0', otherwise
yields the second expr.
expr & expr
yields the first expr if neither expr is null or `0', otherwise
yields `0'.
expr relop expr
where relop is one of < <= = != >= >, yields `1' if the
indicated comparison is true, `0' if false. The comparison is
numeric if both expr are integers, otherwise lexicographic.
expr + expr
expr - expr
addition or subtraction of the arguments.
expr * expr
expr / expr
expr % expr
multiplication, division, or remainder of the arguments.
expr : expr
match expr expr
compares the first argument (a string) with the second argument
(a regular expression); regular expression syntax is the same as
that of ed(1). The \(...\) pattern symbols can be used to
select a portion of the first argument. Otherwise, this
operator yields the number of characters matched (`0' on
failure).
index expr expr
finds the second argument (a string) in the first. Returns the
location of the first matched character (where the first
character is at location `1') or `0' if the second argument is
not a substring of the first.
substr expr expr expr
returns the substring of the first argument (a string) that
starts at the position specified by the second argument (where
`1' refers to the first character) and has length equal to the
third argument (a numeral).
length expr
returns the length of the argument (a string).
( expr )
parentheses for grouping.
Examples:
To add 1 to the shell variable a:
a=`expr $a + 1`
To find the filename part (least significant part) of the pathname
stored in variable a, which may or may not contain `/':
expr $a : ´.*/\(.*\)´ ´|´ $a
Note the quoted shell metacharacters.
SEE ALSOsh(1), test(1)DIAGNOSTICS
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.
7th Edition April 29, 1985 EXPR(1)