EXPR(1)                                                   EXPR(1)



     NAME
          expr - evaluate arguments as an expression

     SYNOPSIS
          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, 2s
          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)                                                   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).

     DIAGNOSTICS
          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.

          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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     EXPR(1)                                                   EXPR(1)



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

               expr  X$a  =  X=

     ORIGIN
          AT&T V.3
















































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