expr(1)                                                   expr(1)



     NAME
          expr - evaluate arguments as an expression

     SYNOPSIS
          expr arguments

     DESCRIPTION
          expr evaluates its arguments as an expression and writes the
          result on the standard output.  Terms of the expression must
          be separated by blanks.  Characters special to the Bourne
          shell or Korn shell (sh (1) or ksh (1), respectively) must
          be escaped.  (expr is replaced in the C shell (csh (1)) by
          @.)  Note that 0 is returned to indicate a zero value, rath-
          er than the null string.  Strings containing blanks or other
          special characters should be quoted.  Integer-valued argu-
          ments 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 opera-
          tors grouped within {} symbols.

          expr \| expr
             returns the first expr if it is neither null nor 0, oth-
             erwise returns the second expr.

          expr \& expr
             returns the first expr if neither expr is null or 0, oth-
             erwise returns 0.

          expr { =, \>, \>=, \<, \<=, != } expr
             returns the result of an integer comparison if both argu-
             ments 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).  Alterna-
             tively, the .) pattern symbols can be used to return a



     April, 1990                                                     1

     expr(1)                                                   expr(1)



             portion of the first argument.

     EXAMPLES
               a=`expr $a + 1`

          adds 1 to the shell variable a.

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

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

          A better representation of above example:

               expr //$a : '.*/\(.*\)'

          the addition of the // characters eliminates any ambiguity
          about the division operator and simplifies the whole expres-
          sion.

               expr $VAR  :  '.*'

          returns the number of characters in $VAR.

     FILES
          /bin/expr

     SEE ALSO
          csh(1), ed(1), ksh(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:



     2                                                     April, 1990

     expr(1)                                                   expr(1)



               expr  $a  =  '='

          looks like:

               expr  =  =  =

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

               expr  X$a  =  X=













































     April, 1990                                                     3