NAME
       expr - Evaluate an expression

SYNOPSIS
       expr arg ?arg arg ...?


DESCRIPTION
       Concatenates arg's (adding separator spaces between them),
       evaluates the result as a Tcl expression, and returns  the
       value.   The  operators permitted in Tcl expressions are a
       subset of the operators permitted in  C  expressions,  and
       they  have  the  same meaning and precedence as the corre-
       sponding C operators.   Expressions  almost  always  yield
       numeric  results  (integer or floating-point values).  For
       example, the expression
              expr 8.2 + 6
       evaluates to 14.2.  Tcl expressions differ from C  expres-
       sions  in  the way that operands are specified.  Also, Tcl
       expressions support non-numeric operands and  string  com-
       parisons.

OPERANDS
       A  Tcl  expression  consists of a combination of operands,
       operators, and  parentheses.   White  space  may  be  used
       between  the operands and operators and parentheses; it is
       ignored by the expression's instructions.  Where possible,
       operands  are interpreted as integer values.  Integer val-
       ues may be specified in  decimal  (the  normal  case),  in
       octal  (if the first character of the operand is 0), or in
       hexadecimal (if the first two characters  of  the  operand
       are  0x).   If an operand does not have one of the integer
       formats given above, then it is  treated  as  a  floating-
       point  number if that is possible.  Floating-point numbers
       may be specified in any of the ways accepted by  an  ANSI-
       compliant  C compiler (except that the f, F, l, and L suf-
       fixes will not be permitted in most  installations).   For
       example,  all  of  the  following are valid floating-point
       numbers:  2.1, 3., 6e4, 7.91e+16.  If no numeric interpre-
       tation  is  possible,  then an operand is left as a string
       (and only a limited set of operators  may  be  applied  to
       it).

       Operands may be specified in any of the following ways:

       [1]    As  an  numeric  value, either integer or floating-
              point.

       [2]    As a Tcl variable, using standard $ notation.   The
              variable's value will be used as the operand.

       [3]    As a string enclosed in double-quotes.  The expres-
              sion parser will perform backslash,  variable,  and
              command  substitutions  on  the information between
              the quotes, and use  the  resulting  value  as  the
              operand

       [4]    As  a  string  enclosed  in braces.  The characters
              between the open brace  and  matching  close  brace
              will  be  used as the operand without any substitu-
              tions.

       [5]    As a Tcl command enclosed in brackets.  The command
              will be executed and its result will be used as the
              operand.

       [6]    As a mathematical function whose arguments have any
              of  the  above forms for operands, such as sin($x).
              See below for a list of defined functions.

       Where  substitutions  occur  above  (e.g.  inside   quoted
       strings),  they are performed by the expression's instruc-
       tions.  However, an additional layer of  substitution  may
       already  have  been performed by the command parser before
       the expression processor was called.  As discussed  below,
       it  is  usually  best  to enclose expressions in braces to
       prevent the command parser from  performing  substitutions
       on the contents.

       For some examples of simple expressions, suppose the vari-
       able a has the value 3 and the variable b has the value 6.
       Then  the  command  on  the left side of each of the lines
       below will produce the value on  the  right  side  of  the
       line:
              expr 3.1 + $a           6.1
              expr 2 + "$a.$b"        5.6
              expr 4*[llength "6 2"]  8
              expr {{word one} < "word $a"}0

OPERATORS
       The  valid operators are listed below, grouped in decreas-
       ing order of precedence:

       -  +  ~  !          Unary minus, unary plus, bit-wise NOT,
                           logical  NOT.   None of these operands
                           may be applied to string operands, and
                           bit-wise  NOT  may  be applied only to
                           integers.

       *  /  %             Multiply, divide, remainder.  None  of
                           these   operands  may  be  applied  to
                           string operands, and remainder may  be
                           applied only to integers.  The remain-
                           der will always have the same sign  as
                           the  divisor  and  an  absolute  value
                           smaller than the divisor.

       +  -                Add  and  subtract.   Valid  for   any
                           numeric operands.

       <<  >>              Left and right shift.  Valid for inte-
                           ger  operands  only.   A  right  shift
                           always propagates the sign bit.

       <  >  <=  >=        Boolean  less,  greater,  less than or
                           equal,  and  greater  than  or  equal.
                           Each operator produces 1 if the condi-
                           tion  is  true,  0  otherwise.   These
                           operators may be applied to strings as
                           well as  numeric  operands,  in  which
                           case string comparison is used.

       ==  !=              Boolean  equal  and  not  equal.  Each
                           operator produces a  zero/one  result.
                           Valid for all operand types.

       &                   Bit-wise   AND.    Valid  for  integer
                           operands only.

       ^                   Bit-wise  exclusive  OR.   Valid   for
                           integer operands only.

       |                   Bit-wise   OR.    Valid   for  integer
                           operands only.

       &&                  Logical AND.  Produces a 1  result  if
                           both  operands  are non-zero, 0 other-
                           wise.  Valid for boolean  and  numeric
                           (integers  or floating-point) operands
                           only.

       ||                  Logical OR.  Produces a  0  result  if
                           both  operands  are zero, 1 otherwise.
                           Valid for boolean and  numeric  (inte-
                           gers or floating-point) operands only.

       x?y:z               If-then-else, as in C.  If x evaluates
                           to  non-zero,  then  the result is the
                           value of y.  Otherwise the  result  is
                           the  value  of  z.  The x operand must
                           have a numeric value.

       See the C manual for more details on the results  produced
       by each operator.  All of the binary operators group left-
       to-right within the same precedence level.   For  example,
       the command
              expr 4*2 < 7
       returns 0.

       The  &&,  ||,  and  ?: operators have ``lazy evaluation'',
       just as in C, which means that operands are not  evaluated
       if  they  are  not  needed  to determine the outcome.  For
       example, in the command
              expr {$v ? [a] : [b]}
       only one of [a] or [b] will actually be evaluated, depend-
       ing  on the value of $v.  Note, however, that this is only
       true if the entire expression is enclosed in braces;  oth-
       erwise  the  Tcl  parser  will  evaluate  both [a] and [b]
       before invoking the expr command.

MATH FUNCTIONS
       Tcl  supports  the  following  mathematical  functions  in
       expressions:

              acos        cos         hypot      sinh
              asin        cosh        log        sqrt
              atan        exp         log10      tan
              atan2       floor       pow        tanh
              ceil        fmod        sin

       Each  of these functions invokes the math library function
       of the same name;  see the manual entries for the  library
       functions  for  details  on what they do.  Tcl also imple-
       ments the following functions for conversion between inte-
       gers and floating-point numbers and the generation of ran-
       dom numbers:

       abs(arg)
              Returns the absolute value  of  arg.   Arg  may  be
              either integer or floating-point, and the result is
              returned in the same form.

       double(arg)
              If arg is a floating value, returns arg,  otherwise
              converts  arg to floating and returns the converted
              value.

       int(arg)
              If arg is an integer value, returns arg,  otherwise
              converts  arg  to integer by truncation and returns
              the converted value.

       rand() Returns a floating point number from zero  to  just
              less  than one or, in mathematical terms, the range
              [0,1).  The seed comes from the internal  clock  of
              the  machine  or  may  be set manual with the srand
              function.

       round(arg)
              If arg is an integer value, returns arg,  otherwise
              converts arg to integer by rounding and returns the
              converted value.

       srand(arg)
              The arg, which must be an integer, is used to reset
              the  seed for the random number generator.  Returns
              the first  random  number  from  that  seed.   Each
              interpreter has it's own seed.

       In  addition  to  these predefined functions, applications
       may  define  additional  functions  using  Tcl_CreateMath-
       Func().

TYPES, OVERFLOW, AND PRECISION
       All internal computations involving integers are done with
       the C type long, and all internal  computations  involving
       floating-point are done with the C type double.  When con-
       verting a string to floating-point, exponent  overflow  is
       detected  and  results  in a Tcl error.  For conversion to
       integer from string, detection of overflow depends on  the
       behavior  of  some  routines in the local C library, so it
       should be regarded as unreliable.  In  any  case,  integer
       overflow and underflow are generally not detected reliably
       for intermediate  results.   Floating-point  overflow  and
       underflow  are  detected  to  the  degree supported by the
       hardware, which is generally pretty reliable.

       Conversion among  internal  representations  for  integer,
       floating-point,  and string operands is done automatically
       as needed.  For arithmetic computations, integers are used
       until  some  floating-point  number  is  introduced, after
       which floating-point is used.  For example,
              expr 5 / 4
       returns 1, while
              expr 5 / 4.0
              expr 5 / ( [string length "abcd"] + 0.0 )
       both  return  1.25.   Floating-point  values  are   always
       returned  with a ``.''  or an e so that they will not look
       like integer values.  For example,
              expr 20.0/5.0
       returns 4.0, not 4.


STRING OPERATIONS
       String values may be used as operands  of  the  comparison
       operators,  although  the expression evaluator tries to do
       comparisons as integer or floating-point when it can.   If
       one  of  the  operands of a comparison is a string and the
       other has a numeric value, the  numeric  operand  is  con-
       verted  back to a string using the C sprintf format speci-
       fier %d for integers and  %g  for  floating-point  values.
       For example, the commands
              expr {"0x03" > "2"}
              expr {"0y" < "0x12"}
       both return 1.  The first comparison is done using integer
       comparison, and the second is done using string comparison
       after  the  second  operand is converted to the string 18.
       Because of Tcl's tendency to treat values as numbers when-
       ever possible, it isn't generally a good idea to use oper-
       ators like == when you really want string  comparison  and
       the  values of the operands could be arbitrary;  it's bet-
       ter in these cases  to  use  the  string  compare  command
       instead.


PERFORMANCE CONSIDERATIONS
       Enclose  expressions  in braces for the best speed and the
       smallest storage requirements.  This allows the Tcl  byte-
       code compiler to generate the best code.

       As  mentioned  above,  expressions  are substituted twice:
       once by the Tcl parser and once by the expr command.   For
       example, the commands
              set a 3
              set b {$a + 2}
              expr $b*4
       return  11,  not a multiple of 4.  This is because the Tcl
       parser will first substitute $a + 2 for  the  variable  b,
       then  the  expr  command will evaluate the expression $a +
       2*4.

       Most expressions do not require a second round of  substi-
       tutions.   Either  they are enclosed in braces or, if not,
       their variable and command substitutions yield numbers  or
       strings that don't themselves require substitutions.  How-
       ever, because a few unbraced expressions need  two  rounds
       of  substitutions,  the  bytecode compiler must emit addi-
       tional instructions to handle this  situation.   The  most
       expensive  code  is required for unbraced expressions that
       contain command substitutions.  These expressions must  be
       implemented  by  generating new code each time the expres-
       sion is executed.


KEYWORDS
       arithmetic, boolean, compare, expression, fuzzy comparison
