ModelSim SE User's Manual - Electrical and Computer Engineering

UM-476 20 - Tcl and macros (DO files)
if command syntax
ModelSim SE User’s Manual
\xhh The hexadecimal digits hh give the hexadecimal value of the
character. Any number of digits may be present.
Backslash substitution is not performed on words enclosed in braces, except for
backslash-newline as described above.
9 If a hash character ("#") appears at a point where Tcl is expecting the first character of
the first word of a command, then the hash character and the characters that follow it, up
through the next newline, are treated as a comment and ignored. The comment character
only has significance when it appears at the beginning of a command.
10 Each character is processed exactly once by the Tcl interpreter as part of creating the
words of a command. For example, if variable substitution occurs then no further
substitutions are performed on the value of the variable; the value is inserted into the
word verbatim. If command substitution occurs then the nested command is processed
entirely by the recursive call to the Tcl interpreter; no substitutions are performed before
making the recursive call and no additional substitutions are performed on the result of
the nested script.
11 Substitutions do not affect the word boundaries of a command. For example, during
variable substitution the entire value of the variable becomes part of a single word, even
if the variable's value contains spaces.
The Tcl if command executes scripts conditionally. Note that in the syntax below the "?"
indicates an optional argument.
Syntax
if expr1 ?then? body1 elseif expr2 ?then? body2 elseif ... ?else? ?bodyN?
Description
The if command evaluates expr1 as an expression. The value of the expression must be a
boolean (a numeric value, where 0 is false and anything else is true, or a string value such
as true or yes for true and false or no for false); if it is true then body1 is executed by
passing it to the Tcl interpreter. Otherwise expr2 is evaluated as an expression and if it is
true then body2 is executed, and so on. If none of the expressions evaluates to true then
bodyN is executed. The then and else arguments are optional "noise words" to make the
command easier to read. There may be any number of elseif clauses, including zero. BodyN
may also be omitted as long as else is omitted too. The return value from the command is
the result of the body script that was executed, or an empty string if none of the expressions
was non-zero and there was no bodyN.