


      EXPR(1)                     (UNIX 5.0)                    EXPR(1)



      NAME
           expr - 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
           quoted.  Integer-valued arguments may be preceded by a unary
           minus sign.  Internally, integers are treated as 32-bit, 2'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 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
                addition or subtraction of integer-valued arguments.

           expr { \*, /, % } expr
                multiplication, division, or remainder of the integer-
                valued arguments.

           expr : expr
                The matching operator : compares the first argument
                with the second argument which must be a regular
                expression; 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 be used to return a portion of the



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      EXPR(1)                     (UNIX 5.0)                    EXPR(1)



                first argument.

      EXAMPLES
           1.   a=`expr $a + 1`

                     adds 1 to the shell variable a.

           2.   #  'For $a equal to either "/usr/abc/file" or just
                "file"'
                expr  $a  :  '.*/\(.*\)'  \|  $a

                     returns the last segment of a path name (i.e.,
                     file).  Watch out for / alone as an argument:
                     expr will take it as the division operator (see
                     BUGS below).

           3.   #  A better representation of example 2.
                expr  //$a  :  '.*/\(.*\)'

                     The addition of the // characters eliminates any
                     ambiguity about the division operator and
                     simplifies the whole expression.

           4.   expr  $VAR  :  '.*'

                     returns the number of characters in $VAR.

      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

      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  =  =  =



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           as the arguments are passed to expr (and they will all be
           taken as the = operator).  The following works:

                expr  X$a  =  X=



















































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