EXPR(1)             RISC/os Reference Manual              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 pre-
     ceded 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 \(...\)



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EXPR(1)             RISC/os Reference Manual              EXPR(1)



          pattern symbols can be used to return a portion of the
          first argument.

INTERNATIONAL FUNCTIONALITY
     expr can process characters from supplementary code sets in
     addition to ASCII characters.  In regular expressions, pat-
     tern searches are performed on characters, not bytes.

WARNING
     : returns the matched size in bytes, not in characters.

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 addi-
     tion 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
          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:



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EXPR(1)             RISC/os Reference Manual              EXPR(1)



          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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