PERL Expressions

The WebCom form processor supports setting of parameters (variables) using simple perl arithmetic, string, regular expressions and miscellaneous functions as follows:

$variable_name=<PERL expression>;

You can calculate the value of a variable using any of the following arithmetic operators: + (addition), - (subtraction), * (multiplication), / (division), % (percentage), ** (exponentiation) (the increment and decrement operators, ++ and --, are not supported). Standard algebraic precedence applies, and can be overridden with parentheses. These operators can be used on literal numeric operands (numbers) as well as on other variables.

You can also use the PERL arithmetic functions:

• atan2(EXPR) - arctangent of X/Y in the range pi to - pi
• cos(EXPR) - cosine
• hex(EXPR) - decimal value of EXPR interpreted as hex string
• index(STR,SUBSTR,POSITION) returns the position of the first occurrence of SUBSTR in STR. The POSITION, if specified, says where to start looking. Positions are based at 0. If SUBSTR is not found, -1 is returned.
• int(EXPR) - the integer portion of EXPR
• length(EXPR) - length in characters of the value of EXPR
• log(EXPR) - logarithm of EXPR
• oct(EXPR) - the decimal value of EXPR interpreted as an octal string
• ord(EXPR) - the numeric ASCII value of the first character of EXPR
• rindex(STR,SUBSTR,POSITION) - just like index except returns the position of the last occurrence of SUBSTR in STR
• sin(EXPR) - "Sorry, there's nothing wicked about this function. It merely returns the sine of EXPR."
• sqrt(EXPR) - square root of expression

Examples:

$order_subtotal=$item1_amt + $item2_amt + $item3_amt + $item4_amt;
$order_tax=int($order_subtotal*8.25)/100;

You can use simple PERL string expressions to set parameters/variables to string values. The most basic string expression sets a variable to a literal string (character) value:

$email="myaddress@mydom.com";

Another basic string expression is to concatenate strings together. In PERL expressions, this is done with the . (period) operator:

$screen="www/".$selected_directory."/".$selected_file;

Or, more simply:

$screen="www/$selected_directory/$selected_file";

You can also use the PERL string functions substr and sprintf:

• sprintf(FORMAT,LIST) - returns a string formatted by the usual printf conventions. The FORMAT string contains text with embedded field specifiers into which the elements of list are substituted, one per field. Field specifiers are roughly of the form:
  %m.nx
  where the m and n are optional sizes whose interpretation depends on the type of field, and x is one of:
• s String
• c Character
• d Decimal number
• ld Long decimal number
• u Unsigned decimal number
• lu Long unsigned decimal number
• x Hexadecimal number
• lx Long hexadecimal number
• o Octal number
• lo Long octal number
• e Exponential format floating-point number
• f Fixed point format floating-point number
• g Compact format floating-point number


Example:
$order_total=sprintf("%-20s %5.2f","Your total is:",$order_total_amt);
(Use a negative length in the format specifier to use left justification instead of right justification)

• substr(EXPR,OFFSET,LENGTH) - the substring of EXPR starting at OFFSET with a length of LENGTH characters (first character is at OFFSET 0).

Examples:

$first_initial_and_comma=substr($first_name,0,1).",";
$order_total=sprintf("%8.2f",$order_subtotal+order_tax);

You can use regular expression substitutions to change the value of a variable. For example, to change all strings of whitespace to a single space:

$variable =~ s/\s*/ /;

You can use the following miscellaneous functions to set values in your form processor application:

• sleep(EXPR) - sleeps for EXPR seconds. Useful for "Server push" applications such as animations to pause between multi-part mimes. It doesn't return a value, but in order to invoke it you do need to include it in an expression. Just use a "dummy" variable:
  $dummy_return = sleep(5); # pause for 5 seconds
• rand(EXPR) - a random fractional number between 0 and the value of EXPR. You should first use srand() to scramble the seed, e.g.:
  $dummy_return=srand(); # return value not used, but form processor only supports perl expressions for setting variable values
  $dice_roll=int(rand(6))+1;
• srand(EXPR) - sets the seed for the rand function
• time() - number of non-leap seconds since January 1, 1970

Refer to the PERL Home Page for additional resources for learning about about PERL expressions (The Llama book is probably the best resource).