Tcl

Tcl, aka Tool Command Language, is an open source programming language created in 1988 by John Ousterhout.

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Tcl (pronounced "tickle" or tee cee ell, ) is a high-level, general-purpose, interpreted, dynamic programming language. It was designed with the goal of being very simple but powerful. Tcl casts everything into the mold of a command, even programming constructs like variable assignment and procedure definition. Read more on Wikipedia...

Tcl website
Tcl Wikipedia page
PLDB has 2 documentation sites for Tcl: www.tcl.tk, devdocs.io
There are at least 13,969 Tcl repos on GitHub
file extensions for Tcl include tcl, tbc, adp, tclin, tm and rvt
The Google BigQuery Public Dataset GitHub snapshot shows 7k users using Tcl in 8k repos on GitHub
There are 71 Project Euler users using Tcl
Explore Tcl snippets on Rosetta Code
Tcl appears in the TIOBE Index
Tcl Ubuntu package
CodeMirror package for syntax highlighting Tcl
Monaco package for syntax highlighting Tcl
Pygments supports syntax highlighting for Tcl
GitHub supports syntax highlighting for Tcl
Tcl appears in the Quine Relay project
There is 1 Jupyter Kernel for Tcl
Release Notes for Tcl
Official Blog page for Tcl
See also: (22 related languages)awk, Lisp, PHP, Tea, PowerShell, C, Python, Expect, Unicode, Regular Expressions, Java, Unix, Linux, Bourne shell, XOTcl, Snit, Verilog, VHDL, UDP, MySQL, PostgreSQL, SQLite

Example from Riju:

puts {Hello, world!}

Example from hello-world:

puts "Hello World"

Example from the Hello World Collection:

#!/usr/local/bin/tclsh
# Hello World in Tcl

puts "Hello World!"

Example from Linguist:

# XDG Base Directory Specification handling
#
# Copyright (C) 2013 Lawrence Woodman
#
# Licensed under an MIT licence.  Please see LICENCE.md for details.
#
# For XDG Base Directory Specification
#   http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html
#
package require Tcl 8.5

namespace eval XDG {
  variable DEFAULTS ""
  namespace export DATA_HOME CONFIG_HOME CACHE_HOME
  namespace export RUNTIME_DIR DATA_DIRS CONFIG_DIRS
}

proc XDG::SetDefaults {} {
  variable DEFAULTS
  if {$DEFAULTS ne ""} return
  set DEFAULTS [list \
    DATA_HOME   [file join $::env(HOME) .local share] \
    CONFIG_HOME [file join $::env(HOME) .config] \
    CACHE_HOME  [file join $::env(HOME) .cache] \
    DATA_DIRS   [list [file join /usr local share] [file join /usr share]] \
    CONFIG_DIRS [list [file join /etc xdg ]]
  ]
}

proc XDG::XDGVarSet {var} {
  expr {[info exists ::env(XDG_$var)] && $::env(XDG_$var) ne ""}
}

proc XDG::Dir {var {subdir ""} } {
  variable DEFAULTS
  SetDefaults
  set dir [dict get $DEFAULTS $var]

  if {[XDGVarSet $var]} {
    set dir $::env(XDG_$var)
  }

  return [file join $dir $subdir]
}

proc XDG::Dirs {var {subdir ""} } {
  variable DEFAULTS
  SetDefaults
  set rawDirs [dict get $DEFAULTS $var]

  if {[XDGVarSet $var]} {
    set rawDirs [split $::env(XDG_$var) ":"]
  }

  set outDirs {}
  foreach dir $rawDirs {
    lappend outDirs [file join $dir $subdir]
  }
  return $outDirs
}

# The remaining procs reference the environmental variables XDG_
# followed by the proc name.
proc XDG::DATA_HOME {{subdir ""}} {Dir DATA_HOME $subdir}
proc XDG::CONFIG_HOME {{subdir ""}} {Dir CONFIG_HOME $subdir}
proc XDG::CACHE_HOME {{subdir ""}} {Dir CACHE_HOME $subdir}

proc XDG::RUNTIME_DIR {{subdir ""}} {
  if {![XDGVarSet RUNTIME_DIR]} { return {} }
  return [file join $::env(XDG_RUNTIME_DIR) $subdir]
}

# The following procs returning the directories as a list with the most
# important first.
proc XDG::DATA_DIRS {{subdir ""}} {Dirs DATA_DIRS $subdir}
proc XDG::CONFIG_DIRS {{subdir ""}} {Dirs CONFIG_DIRS $subdir}

Example from Wikipedia:

oo::class create fruit {
    method eat {} {
        puts "yummy!"
    }
}
oo::class create banana {
    superclass fruit
    constructor {} {
        my variable peeled
        set peeled 0
    }
    method peel {} {
        my variable peeled
        set peeled 1
        puts "skin now off"
    }
    method edible? {} {
        my variable peeled
        return $peeled
    }
    method eat {} {
        if {![my edible?]} {
            my peel
        }
        next
    }
}
set b [banana new]
$b eat               → prints "skin now off" and "yummy!"
fruit destroy
$b eat               → error "unknown command"

Feature	Supported	Token	Example
Strings	✓	"	"Hello world"
Print() Debugging	✓	puts
Line Comments	✓	#	# A comment
Comments	✓
Case Insensitive Identifiers	X
Semantic Indentation	X
MultiLine Comments	X

Tcl - Programming language

Language features