expr(1)expr(1)Nameexpr - evaluate expressions
The arguments are taken as an expression. After evaluation, the result
is written on the standard output. Each token of the expression is a
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 The relop is one of < <= = != >= > and yields 1 if
the indicated comparison is true, 0 if false. The
comparison is numeric if both expr are integers,
expr + expr
expr - expr
Yields addition or subtraction of the arguments.
expr * expr
expr / expr
expr % expr
Yields multiplication, division, or remainder of
expr : expr
match string expr
The matching operators and compare the string first
argument with the regular expression second argu‐
ment; regular expression syntax is the same as that
of The \(...\) pattern symbols can be used to
select a portion of the first argument. Otherwise,
the matching operator returns the number of charac‐
ters matched (0 on failure).
( expr ) Parentheses for grouping.
To lexically compare two special characters, such as with you must pre‐
cede them with identical nonspecial characters. To lexically compare
any two operators, such as with you must precede them with identical,
nonoperator characters. For example:
expr "X(" ">" "X)"
expr "S+" | expr "S-"
The first example adds 1 to the shell variable a:
a=`expr $a + 1`
The second example finds the file name part (least significant part) of
the pathname stored in variable a,
expr $a : ´.*/\(.*\)´ ´|´ $a
Note the quoted shell metacharacters.
The command returns the following exit codes:
0 The expression is neither null nor 0.
1 The expression is null or 0.
2 The expression is invalid.
See Alsoed(1), sh(1), test(1)expr(1)