EXPR(1)                              SysV                              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 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 takes it as the division
               operator (see BUGS below).

     3.   expr  $VAR  :  '.*'

               returns the number of characters in $VAR.

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  =  =  =

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

          expr  X$a  =  X=

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

SEE ALSO
     ed(1), sh(1).