232 lines
7.2 KiB
HTML
232 lines
7.2 KiB
HTML
<html>
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<head>
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<!-- This file has been generated by unroff 1.0, 03/21/96 19:29:46. -->
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<!-- Do not edit! -->
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<link rev="made" href="mailto:net@informatik.uni-bremen.de">
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<title>unroff Programmer's Manual, section 11.</title>
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</head><body>
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<h2><a name="section11">11.</a> <tt> </tt>String Functions
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</h2>
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<p>
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 <tt> </tt> <tt> </tt> <tt> </tt>Most of the string handling primitives described in this section
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could as well have been implemented in Scheme based on the standard
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Scheme string primitives.<tt> </tt>
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They are provided as built-in primitives by
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<i>unroff
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</i>mainly as optimizations or because writing them as Scheme
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procedures would have been significantly more cumbersome.<tt> </tt>
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All the string functions return new strings, that is, they
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do not modify their arguments.<tt> </tt>
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<h2>
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(concat <i>.</i> <i>args</i>)
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</h2>
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<p>
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 <tt> </tt> <tt> </tt> <tt> </tt><i>concat
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</i>can be called with any number of Scheme strings, symbols, and
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characters.<tt> </tt>
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The primitive concatenates its arguments and returns the result
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as a string.<tt> </tt>
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<h2>
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(spread)
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</h2>
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<p>
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 <tt> </tt> <tt> </tt> <tt> </tt>This primitive is identical to
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<i>concat</i>,
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except that it delimits its arguments by a space character.<tt> </tt>
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For example, the event procedure for a macro that just
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returns a line consisting of its arguments could be define like this:
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<dl><dt><dd>
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<pre>
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(defmacro 'X
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(lambda (X . words)
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(parse (apply spread words) #\newline)))
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</pre>
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</dl>
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<h2>
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(repeat-string <i>num</i> <i>string</i>)
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</h2>
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<p>
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 <tt> </tt> <tt> </tt> <tt> </tt>Returns a string consisting of the string argument
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<i>string
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</i>repeated
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<i>num
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</i>times.<tt> </tt>
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<h2>
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(string-prune-left <i>string</i> <i>prefix</i> <i>fail</i>)
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</h2>
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<p>
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 <tt> </tt> <tt> </tt> <tt> </tt>This primitive checks whether
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<i>string
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</i>starts with the given string prefix, and if so, returns the rest of
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<i>string
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</i>beginning at the first character position after the initial prefix.<tt> </tt>
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If the strings do not match,
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<i>fail
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</i>is returned (which may an arbitrary object).<tt> </tt>
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Example:
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<dl><dt><dd>
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<pre>
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(string-prune-left "+foo" "+" #f) => "foo"
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(string-prune-left "gulp" "+" #f) => #f
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</pre>
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</dl>
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<h2>
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(string-prune-right <i>string</i> <i>suffix</i> <i>fail</i>)
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</h2>
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<p>
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 <tt> </tt> <tt> </tt> <tt> </tt>This primitive is identical to
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<i>string-prune-left</i>,
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except that it checks for a suffix rather than a prefix,
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that is, whether
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<i>string
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</i>ends with
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<i>suffix</i>.<tt> </tt>
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<h2>
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(string-compose <i>string1</i> <i>string2</i>)
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</h2>
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<p>
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 <tt> </tt> <tt> </tt> <tt> </tt>If the argument
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<i>string2
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</i>begins with a plus sign,
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<i>string-compose
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</i>returns the concatenation of
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<i>string1
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</i>and
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<i>string2
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</i>with the initial plus sign stripped.<tt> </tt>
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If
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<i>string2
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</i>begins with a minus sign,
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it returns a string consisting of
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<i>string1
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</i>with all characters occurring in
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<i>string2
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</i>removed.<tt> </tt>
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Otherwise,
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<i>string-compose
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</i>just returns
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<i>string2</i>.<tt> </tt>
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This primitive is used for the implementation of the option type
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<i>dynstring</i>.<tt> </tt>
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<h2>
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(parse-pair <i>string</i>)
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</h2>
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<p>
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 <tt> </tt> <tt> </tt> <tt> </tt>If
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<i>string
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</i>consists of two parts separated and enclosed by an arbitrary delimiter
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character,
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<i>parse-pair
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</i>returns a cons cell holding the two substrings.<tt> </tt>
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Otherwise, it returns #f.<tt> </tt>
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Example:
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<dl><dt><dd>
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<pre>
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(parse-pair "'foo'bar'") => ("foo" . "bar")
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(parse-pair "hello") => #f
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</pre>
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</dl>
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<h2>
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(parse-triple <i>string</i>)
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</h2>
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<p>
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 <tt> </tt> <tt> </tt> <tt> </tt>This primitive is identical to
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<i>parse-pair</i>,
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except that it breaks up a three-part string rather than a
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two-part string and returns an improper list whose car, cadr,
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and cddr consist of the three substrings<a href="m-notes.html#footnote5">[note 5]</a>
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.<tt> </tt>
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<i>parse-pair
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</i>and
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<i>parse-triple
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</i>are useful mainly for parsing the arguments to troff requests such
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as ``.if'' and ``.tl''.<tt> </tt>
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<h2>
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<a name=".substitute">(substitute <i>string</i> <i>.</i> <i>args</i>)</a></h2>
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<p>
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 <tt> </tt> <tt> </tt> <tt> </tt>This primitive returns a copy of
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<i>string
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</i>in which each sequence of a percent sign, a
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<i>substitution specifier</i>,
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and another percent sign is replaced by another string according
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to the specifier.<tt> </tt>
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Two adjacent percent signs are replaced by a single percent sign.<tt> </tt>
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The following list describes all substitution specifiers together
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with their respective replacements.<tt> </tt>
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<dl>
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<dt><b>macros</b><dd>
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The name of the troff macro package whose macros are recognized,
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that is, the argument to the option
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<b>-m
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</b>(or the empty string if none was specified).<tt> </tt>
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<dt><b>format</b><dd>
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The output format, that is, the argument to the option
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<b>-f
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</b>(or the default output format if the option was omitted).<tt> </tt>
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<dt><b>directory</b><dd>
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The name of the library directory from which
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<i>unroff
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</i>loads its Scheme files.<tt> </tt>
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<dt><b>progname</b><dd>
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The name of the running program (this is used as a prefix in
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error messages and warning messages).<tt> </tt>
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<dt><b>filepos</b><dd>
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A space character followed by the target of the current input
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stream, a colon, the number of the last input line read from
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the stream, and another colon.<tt> </tt>
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If the current input stream is bound to #f, the empty string
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is substituted.<tt> </tt>
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This specifier is useful for displaying error messages or warning messages.<tt> </tt>
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<dt><b>tmpname</b><dd>
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A file name that can be used for a temporary file.<tt> </tt>
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Each use of this specifier creates a new, unique file name.<tt> </tt>
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<dt><b>version</b><dd>
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The program's major and minor version numbers separated by a period.<tt> </tt>
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<dt><b>weekday</b><dd>
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The abbreviated weekday name.<tt> </tt>
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<dt><b>weekday+</b><dd>
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The full weekday name.<tt> </tt>
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<dt><b>weekdaynum</b><dd>
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The weekday (0-6, Sunday is 0).<tt> </tt>
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<dt><b>monthname</b><dd>
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The abbreviated month name.<tt> </tt>
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<dt><b>monthname+</b><dd>
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The full monthname.<tt> </tt>
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<dt><b>day</b><dd>
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The day of the month (01-31).<tt> </tt>
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<dt><b>month</b><dd>
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The month (01-12).<tt> </tt>
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<dt><b>year</b><dd>
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The year.<tt> </tt>
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<dt><b>date</b><dd>
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The date (in the local environment's representation).<tt> </tt>
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<dt><b>time</b><dd>
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The time (in the local environment's representation).<tt> </tt>
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<dt>a positive number <i>n</i><dd>
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The
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<i>n</i>th
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additional argument in the call to the
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<i>substitute
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</i>primitive, which must be a string.<tt> </tt>
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<dt>a <i>string</i><dd>
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<i>string
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</i>is interpreted as the name of an environment variable,
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and the value of this variable is substituted (or the empty
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string if the environment variable is undefined).<tt> </tt>
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</dl>
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<p>
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Examples:
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<dl><dt><dd>
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<pre>
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(substitute "%date% %HOME%") => "04/09/95 /home/kbs/net"
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(substitute "%progname%:%filepos% %1%" "hello")
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=> "unroff: manual.ms:21: hello"
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(load (substitute "%directory%/scm/%format%/m%macros%.scm"))
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</pre>
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</dl>
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<p><hr>
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Markup created by <em>unroff</em> 1.0, <tt> </tt> <tt> </tt>March 21, 1996, <tt> </tt> <tt> </tt>net@informatik.uni-bremen.de</body>
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</html>
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