1 | '\" |
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2 | '\" Copyright (c) 1993 The Regents of the University of California. |
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3 | '\" Copyright (c) 1994-1996 Sun Microsystems, Inc. |
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4 | '\" |
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5 | '\" See the file "license.terms" for information on usage and redistribution |
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6 | '\" of this file, and for a DISCLAIMER OF ALL WARRANTIES. |
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7 | '\" |
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8 | '\" RCS: @(#) $Id: eval.n,v 1.10 2007/12/13 15:22:32 dgp Exp $ |
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9 | '\" |
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10 | .so man.macros |
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11 | .TH eval n "" Tcl "Tcl Built-In Commands" |
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12 | .BS |
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13 | '\" Note: do not modify the .SH NAME line immediately below! |
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14 | .SH NAME |
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15 | eval \- Evaluate a Tcl script |
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16 | .SH SYNOPSIS |
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17 | \fBeval \fIarg \fR?\fIarg ...\fR? |
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18 | .BE |
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19 | |
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20 | .SH DESCRIPTION |
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21 | .PP |
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22 | \fBEval\fR takes one or more arguments, which together comprise a Tcl |
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23 | script containing one or more commands. |
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24 | \fBEval\fR concatenates all its arguments in the same |
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25 | fashion as the \fBconcat\fR command, passes the concatenated string to the |
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26 | Tcl interpreter recursively, and returns the result of that |
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27 | evaluation (or any error generated by it). |
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28 | Note that the \fBlist\fR command quotes sequences of words in such a |
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29 | way that they are not further expanded by the \fBeval\fR command. |
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30 | .SH EXAMPLES |
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31 | Often, it is useful to store a fragment of a script in a variable and |
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32 | execute it later on with extra values appended. This technique is used |
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33 | in a number of places throughout the Tcl core (e.g. in \fBfcopy\fR, |
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34 | \fBlsort\fR and \fBtrace\fR command callbacks). This example shows how |
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35 | to do this using core Tcl commands: |
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36 | .CS |
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37 | set script { |
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38 | puts "logging now" |
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39 | lappend $myCurrentLogVar |
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40 | } |
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41 | set myCurrentLogVar log1 |
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42 | # Set up a switch of logging variable part way through! |
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43 | after 20000 set myCurrentLogVar log2 |
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44 | |
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45 | for {set i 0} {$i<10} {incr i} { |
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46 | # Introduce a random delay |
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47 | after [expr {int(5000 * rand())}] |
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48 | update ;# Check for the asynch log switch |
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49 | \fBeval\fR $script $i [clock clicks] |
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50 | } |
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51 | .CE |
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52 | .PP |
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53 | .VS 8.5 |
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54 | Note that in the most common case (where the script fragment is |
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55 | actually just a list of words forming a command prefix), it is better |
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56 | to use \fB{*}$script\fR when doing this sort of invocation |
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57 | pattern. It is less general than the \fBeval\fR command, and hence |
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58 | easier to make robust in practice. |
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59 | .VE 8.5 |
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60 | The following procedure acts in a way that is analogous to the |
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61 | \fBlappend\fR command, except it inserts the argument values at the |
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62 | start of the list in the variable: |
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63 | .CS |
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64 | proc lprepend {varName args} { |
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65 | upvar 1 $varName var |
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66 | # Ensure that the variable exists and contains a list |
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67 | lappend var |
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68 | # Now we insert all the arguments in one go |
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69 | set var [\fBeval\fR [list linsert $var 0] $args] |
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70 | } |
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71 | .CE |
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72 | .VS 8.5 |
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73 | However, the last line would now normally be written without |
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74 | \fBeval\fR, like this: |
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75 | .CS |
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76 | set var [linsert $var 0 {*}$args] |
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77 | .CE |
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78 | .VE 8.5 |
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79 | |
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80 | .SH "SEE ALSO" |
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81 | catch(n), concat(n), error(n), interp(n), list(n), namespace(n), subst(n), tclvars(n), uplevel(n) |
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82 | |
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83 | .SH KEYWORDS |
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84 | concatenate, evaluate, script |
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