expr(1)
_________________________________________________________________
expr Command
evaluate arguments as an expression
_________________________________________________________________
SYNTAX
expr arguments
DESCRIPTION
The arguments are taken as an expression. After evaluation, the
result is written on the standard output. Terms of the
expression must be separated by blanks. Characters special to
the shell must be escaped. Note that 0 is returned to indicate a
zero value, rather than the null string. Strings containing
blanks or other special characters should be enquoted. Integer-
valued arguments may be preceded by a unary minus sign.
Internally, integers are treated as 32-bit, 2s complement
numbers.
The operators and keywords are listed below. Characters that
need to be escaped in the Bourne shell, sh(1), are preceded by \.
The list is in order of increasing precedence, with equal
precedence operators grouped within {} symbols.
expr \| expr
Returns the first expr if it is neither null nor 0;
otherwise, returns the second expr.
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
Adds or subtracts integer-valued arguments.
expr { \*, /, % } expr
Multiplies, divides, or gives remainder of the integer-
valued arguments.
expr : expr
The matching operator : compares the first argument with the
second argument. Both must be a regular expression.
DG/UX 4.00 Page 1
Licensed material--property of copyright holder(s)
expr(1)
Regular expression syntax is the same as that of ed(1),
except that all patterns are anchored (i.e., 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 return a part of the first
argument.
_________________________________________________________________
EXAMPLES
$ TEST=`expr $VAR1 \& $VAR2`
$ echo $TEST
0
Assuming VAR1 or VAR2 has a value of null or zero, the variable
TEST will get the value 0, as shown above. If VAR1 and VAR2 both
had some value other than null or zero, the value of VAR1 would
have been assigned to TEST.
_________________________________________________________________
SEE ALSO
ed(1), sh(1).
EXIT CODE
As a side effect of expression evaluation, expr returns the
following exit values:
0 If the expression is neither null nor 0
1 If the expression is null or 0
2 For invalid expressions.
DIAGNOSTICS
syntax error For operator/operand errors
non-numeric argument
If arithmetic is attempted on such a string
WARNING
Remember that expr's arguments are first seen and processed by
the shell. Here are two examples of problems that can arise:
1. Expr can only distinguish operators and operands (arguments)
DG/UX 4.00 Page 2
Licensed material--property of copyright holder(s)
expr(1)
by their value. Let's suppose that the current value of shell
variable a is a single equals sign (=). The shell will read expr
$a = '=' and turn it into expr = = =. To avoid this kind of
problem, attach a dummy character to both your operands, like
this: expr x$a = x=.
2. When a shell variable has a null value, the shell will take
the variable out of the command before expr gets to see it. This
is particularly troublesome when you want to use \| and \&. For
example, suppose shell variable b is null. The shell will turn
expr $b \| 'test' into
expr \| test. To get around this problem, place double quotes
in the command line around shell variables that might become
null, like this:
expr "$b" \| 'test'.
DG/UX 4.00 Page 3
Licensed material--property of copyright holder(s)