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



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 opera-
     tors 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-SysV)        RISC/os Reference Manual         EXPR(1-SysV)



          first argument.

EXAMPLES
     To add 1 to the shell variable a:

          a=`expr $a + 1`

     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).

     A better representation of the previous 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.

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

          expr  X$a  =  X=



















































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