expr(1)               UNIX System V(Essential Utilities)                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
      length of the expression is limited to 512 characters.

      The operators and keywords are listed below.  Characters that need to be
      escaped in the shell [see 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
           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 bytes matched (0 on failure).  Alternatively, the
           \(...\) pattern symbols can be used to return a portion of the first
           argument.





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expr(1)               UNIX System V(Essential Utilities)                expr(1)


      match expr expr
           Compare 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 number of characters matched (0 on failure) is
           returned.  Alternatively, the \(...\) pattern symbols can be used to
           return a portion of the first argument.

      length string
           Return the length of string.

      substr string index count
           Return the portion of string composed of at most count characters
           starting at the character position of string as expressed by index
           (where the first character of string is index 1, not 0).

      index string character_sequence
           Return the index of the first character in string that is also in
           character_sequence or 0 to indicate no match.

EXAMPLES
      Add 1 to the shell variable a:

            a=`expr $a + 1`

      The following example emulates basename(1)-it returns the last segment of
      the path name $a.  For $a equal to either /usr/abc/file or just file, the
      example
      returns file.  (Watch out for / alone as an argument:  expr takes it as
      the division operator; see the NOTES below.)

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

      Here is a better version of the previous example.  The addition of the //
      characters eliminates any ambiguity about the division operator and
      simplifies the whole expression.

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

      Return the number of characters in $VAR:

            expr $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


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expr(1)               UNIX System V(Essential Utilities)                expr(1)


            2     for invalid expressions.

     syntax error     for operator/operand errors
     non-numeric argument
                       if arithmetic is attempted on such a string

NOTES
      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 taken as the =
      operator).  The following works:

            expr X$a = X=

































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