NAME

       eval - Evaluate a Tcl script

SYNOPSIS

       eval arg ?arg ...?
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DESCRIPTION

       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
       further expanded by the eval command.

EXAMPLES

       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 actually 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 practice.  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 this:

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

SEE ALSO

       catch(3tcl),  concat(3tcl),  error(3tcl),  errorCode(3tcl),  errorInfo(3tcl),  interp(3tcl),  list(3tcl),
       namespace(3tcl), subst(3tcl), uplevel(3tcl)

KEYWORDS

       concatenate, evaluate, script

Tcl                                                                                                   eval(3tcl)