expr man page on QNX

Man page or keyword search:  
man Server   4347 pages
apropos Keyword Search (all sections)
Output format
QNX logo
[printable version]

expr(n)			     Tcl Built-In Commands		       expr(n)

______________________________________________________________________________

NAME
       expr - Evaluate an expression

SYNOPSIS
       expr arg ?arg arg ...?
_________________________________________________________________

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

OPERANDS
       A  Tcl expression consists of a combination of operands, operators, and
       parentheses.  White space may be used between the operands  and	opera‐
       tors  and  parentheses; it is ignored by the expression's instructions.
       Where possible, operands are interpreted as  integer  values.   Integer
       values  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 speci‐
       fied in any of the  ways	 accepted  by  an  ANSI-compliant  C  compiler
       (except	that the f, F, l, and L suffixes 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 interpretation
       is possible (note that all literal operands that	 are  not  numeric  or
       boolean	must be quoted with either braces or with double quotes), then
       an operand is left as a string (and only a limited set of operators may
       be applied to it).

       On  32-bit  systems,  integer  values  MAX_INT (0x7FFFFFFF) and MIN_INT │
       (-0x80000000) will be represented as 32-bit values, and integer	values │
       outside	that  range  will  be represented as 64-bit values (if that is │
       possible at all.)

       Operands may be specified in any of the following ways:

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

       [2]    As a boolean value, using any form understood by string is bool‐
	      ean.

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

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

       [5]    As a string enclosed in braces.  The characters between the open
	      brace and matching close brace will be used as the operand with‐
	      out any substitutions.

       [6]    As a Tcl command enclosed in brackets.  The command will be exe‐
	      cuted and its result will be used as the operand.

       [7]    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 the above substitutions occur (e.g. inside quoted strings),  they
       are  performed  by the expression's instructions.  However, the command
       parser may already have performed one round of substitution 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 variable 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	 decreasing  order  of
       precedence:

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

       *  /  %		   Multiply, divide, remainder.	 None of these	opera‐
			   tors may be applied to string operands, and remain‐
			   der may be applied only to integers.	 The remainder
			   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  integer  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 condition is true, 0 otherwise.	 These	opera‐
			   tors	 may  be applied to strings as well as numeric
			   operands, in which case string comparison is used.

       ==  !=		   Boolean equal and not equal.	  Each	operator  pro‐
			   duces  a  zero/one  result.	 Valid for all operand
			   types.					       │

       eq  ne								       │
			   Boolean string equal and string  not	 equal.	  Each │
			   operator  produces  a zero/one result.  The operand │
			   types are interpreted only as strings.

       &		   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 otherwise.  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 (integers 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 boolean or numeric value.

       See the C manual for more details on the results produced by each oper‐
       ator.   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,  depending  on  the
       value  of  $v.	Note,  however,	 that  this is only true if the entire
       expression is enclosed in braces;  otherwise the Tcl parser will evalu‐
       ate both [a] and [b] before invoking the expr command.

MATH FUNCTIONS
       Tcl  supports  the following mathematical functions in expressions, all
       of which work  solely  with  floating-point  numbers  unless  otherwise
       noted:	  abs	      cosh	  log	     sqrt     acos	  dou‐
       ble	log10	   srand	asin	    exp		pow	   tan
       atan	   floor       rand	  tanh
       atan2	   fmod	       round	  wide	   ceil	       hypot	   sin
       cos	   int	       sinh

       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.

       acos(arg)
	      Returns the arc cosine of arg, in the range [0,pi] radians.  Arg
	      should be in the range [-1,1].

       asin(arg)
	      Returns  the arc sine of arg, in the range [-pi/2,pi/2] radians.
	      Arg should be in the range [-1,1].

       atan(arg)
	      Returns the arc tangent of arg, in the range [-pi/2,pi/2]	 radi‐
	      ans.

       atan2(y, x)
	      Returns  the  arc tangent of y/x, in the range [-pi,pi] radians.
	      x and y cannot both be 0.	 If x  is  greater  than  0,  this  is
	      equivalent to atan(y/x).

       ceil(arg)
	      Returns  the smallest integral floating-point value (i.e. with a
	      zero fractional part) not less than arg.

       cos(arg)
	      Returns the cosine of arg, measured in radians.

       cosh(arg)
	      Returns the hyperbolic cosine of arg.  If the result would cause
	      an overflow, an error is returned.

       double(arg)
	      If  arg  is  a floating-point value, returns arg, otherwise con‐
	      verts arg to floating-point and returns the converted value.

       exp(arg)
	      Returns the exponential of  arg,	defined	 as  e**arg.   If  the
	      result would cause an overflow, an error is returned.

       floor(arg)
	      Returns  the  largest integral floating-point value (i.e. with a
	      zero fractional part) not greater than arg.

       fmod(x, y)
	      Returns the floating-point remainder of the division of x by  y.
	      If y is 0, an error is returned.

       hypot(x, y)
	      Computes the length of the hypotenuse of a right-angled triangle
	      sqrt(x*x+y*y).

       int(arg)
	      If arg is an integer value of the	 same  width  as  the  machine │
	      word,  returns arg, otherwise converts arg to an integer (of the │
	      same size as a machine word, i.e. 32-bits on 32-bit systems, and │
	      64-bits  on  64-bit  systems) by truncation and returns the con‐ │
	      verted value.

       log(arg)
	      Returns the natural logarithm of arg.  Arg must  be  a  positive
	      value.

       log10(arg)
	      Returns  the  base  10 logarithm of arg.	Arg must be a positive
	      value.

       pow(x, y)
	      Computes the value of x raised to the power y.  If  x  is	 nega‐
	      tive, y must be an integer value.

       rand() Returns a pseudo-random floating-point value in the range (0,1).
	      The generator algorithm is a simple linear congruential  genera‐
	      tor that is not cryptographically secure.	 Each result from rand
	      completely determines all future results from  subsequent	 calls
	      to  rand,	 so  rand should not be used to generate a sequence of
	      secrets, such as one-time passwords.  The seed of the  generator
	      is  initialized from the internal clock of the machine or may be
	      set 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.

       sin(arg)
	      Returns the sine of arg, measured in radians.

       sinh(arg)
	      Returns  the  hyperbolic sine of arg.  If the result would cause
	      an overflow, an error is returned.

       sqrt(arg)
	      Returns the square root of arg.  Arg must be non-negative.

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

       tan(arg)
	      Returns the tangent of arg, measured in radians.

       tanh(arg)
	      Returns the hyperbolic tangent of arg.

       wide(arg)
	      Converts arg to an integer value at least 64-bits wide (by sign- │
	      extension if arg is a 32-bit number) if it is not one already.

       In addition to these  predefined	 functions,  applications  may	define
       additional functions using Tcl_CreateMathFunc().

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 converting a string to floating-point,
       exponent overflow is detected and results in a Tcl error.  For  conver‐
       sion  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.	Float‐
       ing-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, except in the case of the eq and ne opera‐ │
       tors.  If one of the operands of a comparison is a string and the other
       has  a numeric value, the numeric operand is converted back to a string
       using the C sprintf format specifier %d for integers and %g for	float‐
       ing-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 val‐
       ues as numbers whenever possible, it isn't generally a good idea to use
       operators like == when you really want string comparison and the values
       of the operands could be arbitrary;  it's better in these cases to  use │
       the eq or ne operators, or the string command instead.

PERFORMANCE CONSIDERATIONS
       Enclose expressions in braces for the best speed and the smallest stor‐
       age requirements.  This allows the Tcl bytecode	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	substitutions.
       Either  they are enclosed in braces or, if not, their variable and com‐
       mand substitutions yield	 numbers  or  strings  that  don't  themselves
       require	substitutions.	 However,  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  substitu‐
       tions.	These  expressions  must be implemented by generating new code
       each time the expression is executed.

EXAMPLES
       Define a procedure that computes an  "interesting"  mathematical	 func‐
       tion:
	      proc calc {x y} {
		  expr { ($x*$x - $y*$y) / exp($x*$x + $y*$y) }
	      }

       Convert polar coordinates into cartesian coordinates:
	      # convert from ($radius,$angle)
	      set x [expr { $radius * cos($angle) }]
	      set y [expr { $radius * sin($angle) }]

       Convert cartesian coordinates into polar coordinates:
	      # convert from ($x,$y)
	      set radius [expr { hypot($y, $x) }]
	      set angle	 [expr { atan2($y, $x) }]

       Print  a	 message  describing  the relationship of two string values to
       each other:
	      puts "a and b are [expr {$a eq $b ? {equal} : {different}}]"

       Set a variable to whether an environment variable is  both  defined  at
       all and also set to a true boolean value:
	      set isTrue [expr {
		  [info exists ::env(SOME_ENV_VAR)] &&
		  [string is true -strict $::env(SOME_ENV_VAR)]
	      }]

       Generate a random integer in the range 0..99 inclusive:
	      set randNum [expr { int(100 * rand()) }]

SEE ALSO
       array(n), for(n), if(n), string(n), Tcl(n), while(n)

KEYWORDS
       arithmetic, boolean, compare, expression, fuzzy comparison

Tcl				      8.4			       expr(n)
[top]
                             _         _         _ 
                            | |       | |       | |     
                            | |       | |       | |     
                         __ | | __ __ | | __ __ | | __  
                         \ \| |/ / \ \| |/ / \ \| |/ /  
                          \ \ / /   \ \ / /   \ \ / /   
                           \   /     \   /     \   /    
                            \_/       \_/       \_/ 
More information is available in HTML format for server QNX

List of man pages available for QNX

Copyright (c) for man pages and the logo by the respective OS vendor.

For those who want to learn more, the polarhome community provides shell access and support.

[legal] [privacy] [GNU] [policy] [cookies] [netiquette] [sponsors] [FAQ]
Tweet
Polarhome, production since 1999.
Member of Polarhome portal.
Based on Fawad Halim's script.
...................................................................
Vote for polarhome
Free Shell Accounts :: the biggest list on the net