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Practical Programming in Tcl & Tk, Third Edition
By Brent B. Welch

Table of Contents
Chapter 1.  Tcl Fundamentals

Hello, World!

Example 1-1 The "Hello, World!" example.
puts stdout {Hello, World!}
=> Hello, World!

In this example, the command is puts, which takes two arguments: an I/O stream identifier and a string. puts writes the string to the I/O stream along with a trailing newline character. There are two points to emphasize:

  • Arguments are interpreted by the command. In the example, stdout is used to identify the standard output stream. The use of stdout as a name is a convention employed by puts and the other I/O commands. Also, stderr is used to identify the standard error output, and stdin is used to identify the standard input. Chapter 9 describes how to open other files for I/O.

  • Curly braces are used to group words together into a single argument. The puts command receives Hello, World! as its second argument.


The braces are not part of the value.

The braces are syntax for the interpreter, and they get stripped off before the value is passed to the command. Braces group all characters, including newlines and nested braces, until a matching brace is found. Tcl also uses double quotes for grouping. Grouping arguments will be described in more detail later.

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