proc
proc
NAMESYNOPSIS
DESCRIPTION
EXAMPLES
SEE ALSO
KEYWORDS
___________________________
NAME
proc − Create a Tcl procedure
SYNOPSIS
proc name args body ___________________________
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 contents 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 created 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 procedure. It consists of a list, possibly empty, each of whose elements specifies one argument. 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. Arguments 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 command 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 formal arguments. 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 current namespace when body is executed will be the namespace that the procedure’s name exists in, which will be the namespace that it was created in unless it has been changed with rename.
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 execute 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
KEYWORDS
argument, procedure
Opportunity
Personal Opportunity - Free software gives you access to billions of dollars of software at no cost. Use this software for your business, personal use or to develop a profitable skill. Access to source code provides access to a level of capabilities/information that companies protect though copyrights. Open source is a core component of the Internet and it is available to you. Leverage the billions of dollars in resources and capabilities to build a career, establish a business or change the world. The potential is endless for those who understand the opportunity.
Business Opportunity - Goldman Sachs, IBM and countless large corporations are leveraging open source to reduce costs, develop products and increase their bottom lines. Learn what these companies know about open source and how open source can give you the advantage.
Free Software
Free Software provides computer programs and capabilities at no cost but more importantly, it provides the freedom to run, edit, contribute to, and share the software. The importance of free software is a matter of access, not price. Software at no cost is a benefit but ownership rights to the software and source code is far more significant.
Free Office Software - The Libre Office suite provides top desktop productivity tools for free. This includes, a word processor, spreadsheet, presentation engine, drawing and flowcharting, database and math applications. Libre Office is available for Linux or Windows.
Free Books
The Free Books Library is a collection of thousands of the most popular public domain books in an online readable format. The collection includes great classical literature and more recent works where the U.S. copyright has expired. These books are yours to read and use without restrictions.
Source Code - Want to change a program or know how it works? Open Source provides the source code for its programs so that anyone can use, modify or learn how to write those programs themselves. Visit the GNU source code repositories to download the source.
Education
Study at Harvard, Stanford or MIT - Open edX provides free online courses from Harvard, MIT, Columbia, UC Berkeley and other top Universities. Hundreds of courses for almost all major subjects and course levels. Open edx also offers some paid courses and selected certifications.
Linux Manual Pages - A man or manual page is a form of software documentation found on Linux/Unix operating systems. Topics covered include computer programs (including library and system calls), formal standards and conventions, and even abstract concepts.
