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5.0 KiB
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117 lines
5.0 KiB
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<HTML><HEAD><TITLE>Tcl Built-In Commands - switch manual page</TITLE></HEAD><BODY>
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<DL>
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<DD><A HREF="switch.htm#M2" NAME="L1160">NAME</A>
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<DL><DD>switch - Evaluate one of several scripts, depending on a given value</DL>
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<DD><A HREF="switch.htm#M3" NAME="L1161">SYNOPSIS</A>
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<DL>
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<DD><B>switch </B>?<I>options</I>?<I> string pattern body </I>?<I>pattern body </I>...?
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<DD><B>switch </B>?<I>options</I>?<I> string </I>{<I>pattern body </I>?<I>pattern body </I>...?}
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</DL>
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<DD><A HREF="switch.htm#M4" NAME="L1162">DESCRIPTION</A>
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<DL>
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<DD><A HREF="switch.htm#M5" NAME="L1163"><B>-exact</B></A>
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<DD><A HREF="switch.htm#M6" NAME="L1164"><B>-glob</B></A>
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<DD><A HREF="switch.htm#M7" NAME="L1165"><B>-regexp</B></A>
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<DD><A HREF="switch.htm#M8" NAME="L1166"><B>- -</B></A>
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</DL>
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<DD><A HREF="switch.htm#M9" NAME="L1167">SEE ALSO</A>
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<DD><A HREF="switch.htm#M10" NAME="L1168">KEYWORDS</A>
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</DL><HR>
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<H3><A NAME="M2">NAME</A></H3>
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switch - Evaluate one of several scripts, depending on a given value
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<H3><A NAME="M3">SYNOPSIS</A></H3>
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<B>switch </B>?<I>options</I>?<I> string pattern body </I>?<I>pattern body </I>...?<BR>
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<B>switch </B>?<I>options</I>?<I> string </I>{<I>pattern body </I>?<I>pattern body </I>...?}<BR>
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<H3><A NAME="M4">DESCRIPTION</A></H3>
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The <B>switch</B> command matches its <I>string</I> argument against each of
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the <I>pattern</I> arguments in order.
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As soon as it finds a <I>pattern</I> that matches <I>string</I> it
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evaluates the following <I>body</I> argument by passing it recursively
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to the Tcl interpreter and returns the result of that evaluation.
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If the last <I>pattern</I> argument is <B>default</B> then it matches
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anything.
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If no <I>pattern</I> argument
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matches <I>string</I> and no default is given, then the <B>switch</B>
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command returns an empty string.
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<P>
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If the initial arguments to <B>switch</B> start with <B>-</B> then
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they are treated as options. The following options are
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currently supported:
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<P>
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<DL>
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<P><DT><A NAME="M5"><B>-exact</B></A><DD>
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Use exact matching when comparing <I>string</I> to a pattern. This
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is the default.
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<P><DT><A NAME="M6"><B>-glob</B></A><DD>
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When matching <I>string</I> to the patterns, use glob-style matching
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(i.e. the same as implemented by the <B><A HREF="../TkCmd/string.htm">string match</A></B> command).
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<P><DT><A NAME="M7"><B>-regexp</B></A><DD>
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When matching <I>string</I> to the patterns, use regular
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expression matching
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(as described in the <B><A HREF="../TkCmd/re_syntax.htm">re_syntax</A></B> reference page).
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<P><DT><A NAME="M8"><B>- -</B></A><DD>
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Marks the end of options. The argument following this one will
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be treated as <I>string</I> even if it starts with a <B>-</B>.
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<P></DL>
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<P>
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Two syntaxes are provided for the <I>pattern</I> and <I>body</I> arguments.
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The first uses a separate argument for each of the patterns and commands;
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this form is convenient if substitutions are desired on some of the
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patterns or commands.
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The second form places all of the patterns and commands together into
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a single argument; the argument must have proper list structure, with
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the elements of the list being the patterns and commands.
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The second form makes it easy to construct multi-line switch commands,
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since the braces around the whole list make it unnecessary to include a
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backslash at the end of each line.
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Since the <I>pattern</I> arguments are in braces in the second form,
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no command or variable substitutions are performed on them; this makes
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the behavior of the second form different than the first form in some
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cases.
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<P>
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If a <I>body</I> is specified as ``<B>-</B>'' it means that the <I>body</I>
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for the next pattern should also be used as the body for this
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pattern (if the next pattern also has a body of ``<B>-</B>''
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then the body after that is used, and so on).
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This feature makes it possible to share a single <I>body</I> among
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several patterns.
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<P>
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Beware of how you place comments in <B>switch</B> commands. Comments
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should only be placed <B>inside</B> the execution body of one of the
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patterns, and not intermingled with the patterns.
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<P>
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Below are some examples of <B>switch</B> commands:
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<PRE><B>switch abc a - b {format 1} abc {format 2} default {format 3}</B></PRE>
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will return <B>2</B>,
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<PRE><B>switch -regexp aaab {
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^a.*b$ -
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b {format 1}
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a* {format 2}
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default {format 3}
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}</B></PRE>
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will return <B>1</B>, and
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<PRE><B>switch xyz {
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a
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-
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b
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{
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# Correct Comment Placement
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format 1
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}
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a*
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{format 2}
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default
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{format 3}
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}</B></PRE>
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will return <B>3</B>.
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<H3><A NAME="M9">SEE ALSO</A></H3>
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<B><A HREF="../TkCmd/for.htm">for</A></B>, <B><A HREF="../TkCmd/if.htm">if</A></B>, <B><A HREF="../TkCmd/regexp.htm">regexp</A></B>
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<H3><A NAME="M10">KEYWORDS</A></H3>
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<A href="../Keywords/S.htm#switch">switch</A>, <A href="../Keywords/M.htm#match">match</A>, <A href="../Keywords/R.htm#regular expression">regular expression</A>
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<HR><PRE>
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<A HREF="../copyright.htm">Copyright</A> © 1993 The Regents of the University of California.
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<A HREF="../copyright.htm">Copyright</A> © 1994-1997 Sun Microsystems, Inc.
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<A HREF="../copyright.htm">Copyright</A> © 1995-1997 Roger E. Critchlow Jr.</PRE>
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</BODY></HTML>
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