eval man page on SmartOS

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eval(n)			     Tcl Built-In Commands		       eval(n)


       eval - Evaluate a Tcl script

       eval arg ?arg ...?

       Eval  takes one or more arguments, which together comprise a Tcl script
       containing one or more commands.	 Eval concatenates all	its  arguments
       in  the	same  fashion  as  the concat command, passes the concatenated
       string to the Tcl interpreter recursively, and returns  the  result  of
       that  evaluation	 (or  any  error generated by it).  Note that the list
       command quotes sequences of words in such a way that they are not  fur‐
       ther expanded by the eval command.

       Often,  it  is useful to store a fragment of a script in a variable and
       execute it later on with extra values appended. This technique is  used
       in a number of places throughout the Tcl core (e.g. in fcopy, lsort and
       trace command callbacks). This example shows how to do this using  core
       Tcl commands:

	      set script {
		  puts "logging now"
		  lappend $myCurrentLogVar
	      set myCurrentLogVar log1
	      # Set up a switch of logging variable part way through!
	      after 20000 set myCurrentLogVar log2

	      for {set i 0} {$i<10} {incr i} {
		  # Introduce a random delay
		  after [expr {int(5000 * rand())}]
		  update    ;# Check for the asynch log switch
		  eval $script $i [clock clicks]

       Note  that  in the most common case (where the script fragment is actu‐
       ally just a list of words forming a command prefix), it	is  better  to
       use  {*}$script when doing this sort of invocation pattern.  It is less
       general than the eval command, and hence easier to make robust in prac‐
       tice.   The  following procedure acts in a way that is analogous to the
       lappend command, except it inserts the argument values at the start  of
       the list in the variable:

	      proc lprepend {varName args} {
		  upvar 1 $varName var
		  # Ensure that the variable exists and contains a list
		  lappend var
		  # Now we insert all the arguments in one go
		  set var [eval [list linsert $var 0] $args]

       However, the last line would now normally be written without eval, like

	      set var [linsert $var 0 {*}$args]

       catch(n), concat(n), error(n), errorCode(n),  errorInfo(n),  interp(n),
       list(n), namespace(n), subst(n), uplevel(n)

       concatenate, evaluate, script

Tcl								       eval(n)

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