87 lines
2.8 KiB
Plaintext
87 lines
2.8 KiB
Plaintext
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'\" Copyright (c) 1993 The Regents of the University of California.
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'\" Copyright (c) 1994-1996 Sun Microsystems, Inc.
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'\"
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'\" See the file "license.terms" for information on usage and redistribution
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'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
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'\"
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'\" SCCS: @(#) foreach.n 1.6 96/03/25 20:15:14
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'\"
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.so man.macros
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.TH foreach n "" Tcl "Tcl Built-In Commands"
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.BS
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'\" Note: do not modify the .SH NAME line immediately below!
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.SH NAME
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foreach \- Iterate over all elements in one or more lists
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.SH SYNOPSIS
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\fBforeach \fIvarname list body\fR
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.br
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\fBforeach \fIvarlist1 list1\fR ?\fIvarlist2 list2 ...\fR? \fIbody\fR
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.BE
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.SH DESCRIPTION
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.PP
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The \fBforeach\fR command implements a loop where the loop
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variable(s) take on values from one or more lists.
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In the simplest case there is one loop variable, \fIvarname\fR,
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and one list, \fIlist\fR, that is a list of values to assign to \fIvarname\fR.
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The \fIbody\fR argument is a Tcl script.
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For each element of \fIlist\fR (in order
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from first to last), \fBforeach\fR assigns the contents of the
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element to \fIvarname\fR as if the \fBlindex\fR command had been used
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to extract the element, then calls the Tcl interpreter to execute
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\fIbody\fR.
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.PP
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In the general case there can be more than one value list
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(e.g., \fIlist1\fR and \fIlist2\fR),
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and each value list can be associated with a list of loop variables
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(e.g., \fIvarlist1\fR and \fIvarlist2\fR).
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During each iteration of the loop
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the variables of each \fIvarlist\fP are assigned
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consecutive values from the corresponding \fIlist\fP.
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Values in each \fIlist\fP are used in order from first to last,
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and each value is used exactly once.
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The total number of loop iterations is large enough to use
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up all the values from all the value lists.
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If a value list does not contain enough
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elements for each of its loop variables in each iteration,
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empty values are used for the missing elements.
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.PP
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The \fBbreak\fR and \fBcontinue\fR statements may be
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invoked inside \fIbody\fR, with the same effect as in the \fBfor\fR
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command. \fBForeach\fR returns an empty string.
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.SH EXAMPLES
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.PP
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The following loop uses i and j as loop variables to iterate over
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pairs of elements of a single list.
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.DS
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set x {}
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foreach {i j} {a b c d e f} {
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lappend x $j $i
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}
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# The value of x is "b a d c f e"
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# There are 3 iterations of the loop.
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.DE
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.PP
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The next loop uses i and j to iterate over two lists in parallel.
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.DS
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set x {}
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foreach i {a b c} j {d e f g} {
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lappend x $i $j
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}
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# The value of x is "a d b e c f {} g"
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# There are 4 iterations of the loop.
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.DE
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.PP
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The two forms are combined in the following example.
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.DS
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set x {}
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foreach i {a b c} {j k} {d e f g} {
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lappend x $i $j $k
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}
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# The value of x is "a d e b f g c {} {}"
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# There are 3 iterations of the loop.
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.DE
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.SH KEYWORDS
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foreach, iteration, list, looping
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