Tcl Tutorial Lesson 30

Modularization - source

The source command will load a file and execute it. This allows a program to be broken up into multiple files, with each file defining procedures and variables for a particular area of functionality. For instance, you might have a file called database.tcl that contains all the procedures for dealing with a database, or a file called gui.tcl that handles creating a graphical user interface with Tk. The main script can then simply include each file using the source command. More powerful techniques for program modularization are discussed with Building reusable libraries

This command can be used to:

  • separate a program into multiple files.
  • make a library file that contains all the procs for a particular set of functions.
  • configure programs.
  • load data files.
source fileName
Reads the script in fileName and executes it.
  • If the script executes successfully, source returns the value of the last statement in the script.
  • If there is an error in the script, source will return that error.
  • If there is a return (other than within a proc definition) then source will return immediately, without executing the remainder of the script.
  • If fileName starts with a tilde (~) then $env(HOME) will be substituted for the tilde, as is done in the file command.



# Example data file to be sourced
set scr [info script]
proc testproc {} {
    global scr
    puts "testproc source file: $scr"
set abc 1
set aaaa 1


set filename "sourcedata.tcl"
puts "Global variables visible before sourcing $filename:"
puts "[lsort [info globals]]\n"

if {[info procs testproc] eq ""} {
    puts "testproc does not exist.  sourcing $filename"
    source $filename

puts "\nNow executing testproc"

puts "Global variables visible after sourcing $filename:"
puts "[lsort [info globals]]\n"

  Resulting output

(slightly edited to make the long list fit)

Global variables visible before sourcing sourcedata.tcl:
argc argv argv0 auto_path env errorCode errorInfo filename
tcl_interactive tcl_library tcl_patchLevel tcl_platform
tcl_rcFileName tcl_version

testproc does not exist.  sourcing sourcedata.tcl

Now executing testproc
testproc source file: sourcedata.tcl
Global variables visible after sourcing sourcedata.tcl:
abc argc argv argv0 auto_path env errorCode errorInfo filename scr
tcl_interactive tcl_library tcl_patchLevel tcl_platform
tcl_rcFileName tcl_version