TCL commands usage

tcl_basic_cmds_usage.tcl

# set, a built-in command, reads and writes variables.
set a 10

# Desc: puts - Write to a channel
# Syntax: puts ?-nonewline? ?channelId? string
  # channelId stdin, stdout, stderr
set abc [puts "test"] 
puts stdout $tcl_version nonewline

# Desc: eval, a built-in Tcl command, interprets its arguments as a script, which it then evaluates.
# Syntax: eval arg ?arg ...?
set b {the total is $20}
# each of the following commands returns a is different result:
set a $b
eval {set a $b}
eval "set a $b"
eval [list set a $b]

# expr, a built-in Tcl command, evaluates an expression.
set a 10
set b 20
set c 100
set res [expr a+b*c] # uses BOMDMAS rule

# Desc: global, a built-in Tcl command, declares global variables.
# Syntax: global varname ?varname ...?
set a 10
proc globalTest {} {
    global a
    puts $a
}

# Description info, a built-in command, provides information about the state of a Tcl interpreter.
    # info option ?arg arg ...?
    # info args procname
    # info body procname
    # info class subcommand class …
    # info cmdcount
    # info commands ?pattern?
    # info complete script
    # info coroutine
    # info default procname arg varname
    # info errorstack
    # info exists varName
    # info frame ?number?
    # info functions pattern
    # info globals ?pattern?
    # info hostname
    # info level ?number?
    # info library
    # info loaded ?interp?
    # info locals ?pattern?
    # info nameofexecutable
    # info object subcommand object …
    # info patchlevel
    # info procs ?pattern?
    # info script ?filename?
    # info sharedlibextension
    # info tclversion
    # info vars ?pattern?

tcl_conditions_loops.tcl

# Desc: if, a built-in Tcl command, conditionally evaluates scripts.
# Syntax: if expr1 ?then? body1 elseif expr2 ?then? body2 elseif ... ?else? ?bodyN?
set a 1
set b stuff
if { $a == 1 ||
    $b eq {nonsense}} {
    puts found
}

# Desc: while - Execute script repeatedly as long as a condition is met
# Syntax: while test body
set x 0
while {$x<10} {
    puts "x is $x"
    incr x
}
 
# Desc: for, a built-in Tcl command, provides an iterative loop construct.
# for start test next body
for {set x 0} {$x<10} {incr x} {
    puts "x is $x"
}

# Desc: [break], a built-in Tcl command, aborts a looping command.
# Syntax: break
for {set x 0} {$x<10} {incr x} {
    if {$x > 5} {
        break
    }
    puts "x is $x"
}

# Desc: continue, a built-in tcl command, skips to the next iteration of a loop
# Syntax: continue
for {set x 0} {$x<10} {incr x} {
    if {$x == 5} {
        continue
    }
    puts "x is $x"
}

# Desc: foreach, a built-in Tcl command, iterates over all elements in one or more lists and evaluates a script at each iteration
# Syntax: foreach varlist list body
    # foreach varlist1 list1 ?varlist2 list2 ... varlistn listn? body
foreach a [list 1 2 3 4] b [list 5 6 7 8] c [list a b c d] d [list w x y z] {
    puts "$a $b $c $d"
}

# Desc: return, a built-in Tcl command, terminates a script, specifying its result.
# Syntax: 
    # return ?result
    # return ?-code code? ?result
    # return ?option value? ?result
        # Options
        # -errorcode list, -errorinfo info, -errorstack list (Added in TCL 8.6), -leval level, -options options
proc foo {} {
    puts Foo
    return
    This is not Tcl - code after the return is never evaluated so 
    may be  used for commenting...
}        

tcl_list_operations.tcl

# List operations
set myList [list 1 2 3 4]

# Desc: lindex, a built-in Tcl command, retrieves an element from a list or a nested list.
# Syntax:
lindex $myList 0

# Desc: llength returns the number of elements in a list.
# Syntax: llength list
llenght $myList

# Desc:lreplace replaces or deletes elements in a list, and can also prepend elements to a list.
# Syntax: lreplace list first last ?element element ...?
lreplace {a b c} 1 1 hello there

# Desc: lappend appends elements to a list.
# Syntax: lappend varName ?value value ...?
lappend auto_path /usr/local/lib/tcl8.5

# Desc: linsert inserts elements into a list.
# Syntax: linsert list index element1 ?element2 element3 ...?
set oldList [list 1 2 3 4]
set myvalue 10
set newList [linsert $oldList 0 myvalue]

# Desc: The lrange command returns one or more adjacent elements from a list.
# Syntax: lrange list first last
set myList [list a b c d]
lrange $myList 0 0  # returns a

# Desc: lsearch searches for elements in a list that match a pattern.
# Syntax: lsearch ?option? list pattern
# Options are
  # MATCHING STYLE OPTIONS
      # -exact, -glob, -regexp, -sorted
  # GENERAL MODIFIER OPTIONS
      # -all, -inline, -not, -start index
  # CONTENTS DESCRIPTION OPTIONS
      # -ascii, -dictionary, -integer, -nocase, -real
  # SORTED LIST OPTIONS
      # -decreasing, -increasing, -bisect, -index indexList, -subindices
set distros {RedHat SUSE Debian Knoppix Peanut Mandrake Slackware}
lsearch $distros RedHat

# Desc: lsort, a built-in Tcl command, sorts elements in a list.
# Syntax: lsort ?options...? list
# Options are 
  # -ascii, -command command, -decreasing, -dictionary, -dictionary mode, -increasing, -index index, -integer, -real
lsort -dic {-5 -10  -1 0 3 1 2} # -1 -5 -10 0 1 2 3