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proc(n) Tcl Built-In Commands proc(n)
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NAME
proc - Create a Tcl procedure
SYNOPSIS
proc name args body
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DESCRIPTION
The proc command creates a new Tcl procedure named name, replacing any existing command or
procedure there may have been by that name. Whenever the new command is invoked, the con-
tents of body will be executed by the Tcl interpreter. Normally, name is unqualified
(does not include the names of any containing namespaces), and the new procedure is cre-
ated in the current namespace. If name includes any namespace qualifiers, the procedure
is created in the specified namespace. Args specifies the formal arguments to the proce-
dure. It consists of a list, possibly empty, each of whose elements specifies one argu-
ment. Each argument specifier is also a list with either one or two fields. If there is
only a single field in the specifier then it is the name of the argument; if there are two
fields, then the first is the argument name and the second is its default value. Argu-
ments with default values that are followed by non-defaulted arguments become required
arguments. In 8.6 this will be considered an error.
When name is invoked a local variable will be created for each of the formal arguments to
the procedure; its value will be the value of corresponding argument in the invoking com-
mand or the argument's default value. Actual arguments are assigned to formal arguments
strictly in order. Arguments with default values need not be specified in a procedure
invocation. However, there must be enough actual arguments for all the formal arguments
that do not have defaults, and there must not be any extra actual arguments. Arguments
with default values that are followed by non-defaulted arguments become required arguments
(in 8.6 it will be considered an error). There is one special case to permit procedures
with variable numbers of arguments. If the last formal argument has the name args, then a
call to the procedure may contain more actual arguments than the procedure has formals.
In this case, all of the actual arguments starting at the one that would be assigned to
args are combined into a list (as if the list command had been used); this combined value
is assigned to the local variable args.
When body is being executed, variable names normally refer to local variables, which are
created automatically when referenced and deleted when the procedure returns. One local
variable is automatically created for each of the procedure's arguments. Other variables
can only be accessed by invoking one of the global, variable, upvar or namespace upvar
commands.
The proc command returns an empty string. When a procedure is invoked, the procedure's
return value is the value specified in a return command. If the procedure does not exe-
cute an explicit return, then its return value is the value of the last command executed
in the procedure's body. If an error occurs while executing the procedure body, then the
procedure-as-a-whole will return that same error.
EXAMPLES
This is a procedure that accepts arbitrarily many arguments and prints them out, one by
one.
proc printArguments args {
foreach arg $args {
puts $arg
}
}
This procedure is a bit like the incr command, except it multiplies the contents of the
named variable by the value, which defaults to 2:
proc mult {varName {multiplier 2}} {
upvar 1 $varName var
set var [expr {$var * $multiplier}]
}
SEE ALSO
info(n), unknown(n)
KEYWORDS
argument, procedure
Tcl proc(n)
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On Apache/2.4.6 (CentOS)
Under GNU General Public License
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