expr.
Here's some excerpts from the man page.
Expr 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 corresponding 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 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 operators and parentheses; it is ignored by the expression processor. 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).
Note that the octal and hexadecimal conversion takes place differently in the expr command than in the Tcl substitution phase.
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. For example, all of the following are valid floating-point numbers: 2.1, 3., 6e4, 7.91e+16. If no numeric interpretation 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:
OPERATORS
The valid operators are listed below, grouped in decreasing order of precedence:
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
TYPE CONVERSIONSTcl supports the following functions to convert from one representation of a number to another:
abs double int round
If you haven't hit the Run Example button yet, do so now, and
examine the results of the example. Play around a bit with the example
code, and then go on to the next lesson.
:TEXT_END:
:LESSON_TEXT_START_LEVEL 1:
The command for doing math type operations
is expr. The following discussion of the expr
command is extracted and adapted from the expr man page.
Expr 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 include all the
standard math functions. Expressions almost always yield numeric
results (integer or floating-point values).
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 processor. 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).
Note that the octal and hexadecimal conversion takes place differently
in the expr command than in the Tcl substitution phase. In the substitution
phase, a \x32 would be converted to an ascii "2", while the expr
command would covert a 0x32 to a decimal 50.
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. For example, all of the following are valid floating-point numbers: 2.1, 3., 6e4, 7.91e+16. If no numeric interpretation 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:
OPERATORS
The valid operators are listed below, grouped in decreasing order of precedence:
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
TYPE CONVERSIONSTcl supports the following functions to convert from one representation of a number to another:
abs double int round
If you haven't hit the Run Example button yet, do so now, and examine
the results of the example. Play around a bit with the example code, and
then go on to the next lesson.
:TEXT_END:
:LESSON_TEXT_START_LEVEL 2:
The driving force for using a computer has traditionally been to perform
mathematic manipulations of data. Some languages like BASIC or C do
math operations whenever they appear in an expression. Tcl, however,
has a special command for doing math operations. The command for doing
mathematic operations is expr. The following discussion of the expr
command is extracted and adapted from the expr man page.
Expr accepts the strings that follow it, evaluates them as a Tcl expression, and returns the value. The operators permitted in Tcl expressions include all the standard math functions. Mathematic expressions always yield numeric results (integer or floating-point values) while logical operations which return boolean (true or false) results.
Like regular arithmetic, the Tcl math expression consists of operators, operands, and parentheses. White space may be used between the operands, operators and parentheses.
An operand is:
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).
Note that the octal and hexadecimal conversion takes place differently in the expr command than in the Tcl substitution phase.
For example, in the Tcl substitution phase, a \x32 (the ascii
code for the number 2) would be converted to an ascii "2" while
0x32 would be converted within the expr command to a
decimal 50.
This code is a true statement:
expr \x32 == 0x2
It is true because
during the substitution phase the \x32 was replaced with an ascii "2",
while the 0x2 was passed to expr unchanged. Expr
then interprets 0x2 as a hexadecimal 2,
compares decimal 2 to hexadecimal 2, and finds that
they are equal, which is obviously true.
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. For example, all of the following are valid floating-point numbers: 2.1, 3., 6e4, 7.91e+16. If no numeric interpretation is possible, then an operand is left as a string (and only a limited set of operators may be applied to it).
If there are no parentheses to explicitly declare the order of operations, then Tcl does arithmetic operations in a particular order, just as you would do them on paper. This is called the order of precedence of the operators.
As you see in the list below, the command expr "5 + -3 * 4" is evaluated in
this order:
Operands may be specified in any of the following ways:
OPERATORS
The valid operators are listed below, grouped in decreasing order of precedence:
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
TYPE CONVERSIONSTcl supports the following functions to convert from one representation of a number to another:
abs double int roundThe
expr command supports most of the standard C library math calls.
If you haven't hit the Run Example button yet, do so now, and examine the results of the example. Play around a bit with the example code, and then go on to the next lesson. :TEXT_END: :CODE_START: set X 100; set Y 256; set Z [expr "$Y + $X"] set Z_LABEL "$Y plus $X is " puts "$Z_LABEL $Z" puts "The square root of $Y is [expr sqrt($Y)]\n" puts "Because of the precedence rules \"5 + -3 * 4\" is: [expr -3 * 4 + 5]" puts "Because of the parentheses \"(5 + -3) * 4\" is: [expr (5 + -3) * 4]" puts "\n................. more examples of differences between \" and \{" puts {$Z_LABEL [expr $Y + $X]} puts "$Z_LABEL {[expr $Y + $X]}" puts "The command to add two numbers is: \[expr \$a + \$b]" :TEXT_END: