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<DL>
<DT><U>Function:</U> int <B>history_search_prefix</B> <I>(const char *string, int direction)</I>
<DD>Search the history for <VAR>string</VAR>, starting at the current history
offset.  The search is anchored: matching lines must begin with
<VAR>string</VAR>.  If <VAR>direction</VAR> is less than 0, then the search is
through previous entries, otherwise through subsequent entries.
If <VAR>string</VAR> is found, then the
current history index is set to that entry, and the return value is 0. 
Otherwise, nothing is changed, and a -1 is returned. 
</DL>
</P><P>

<A NAME="IDX23"></A>
<DL>
<DT><U>Function:</U> int <B>history_search_pos</B> <I>(const char *string, int direction, int pos)</I>
<DD>Search for <VAR>string</VAR> in the history list, starting at <VAR>pos</VAR>, an
absolute index into the list.  If <VAR>direction</VAR> is negative, the search
proceeds backward from <VAR>pos</VAR>, otherwise forward.  Returns the absolute
index of the history element where <VAR>string</VAR> was found, or -1 otherwise.
</DL>
</P><P>

<A NAME="Managing the History File"></A>
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<H3> 2.3.6 Managing the History File </H3>
<!--docid::SEC15::-->
<P>

The History library can read the history from and write it to a file.
This section documents the functions for managing a history file.
</P><P>

<A NAME="IDX24"></A>
<DL>
<DT><U>Function:</U> int <B>read_history</B> <I>(const char *filename)</I>
<DD>Add the contents of <VAR>filename</VAR> to the history list, a line at a time.
If <VAR>filename</VAR> is <CODE>NULL</CODE>, then read from <TT>`~/.history'</TT>.
Returns 0 if successful, or <CODE>errno</CODE> if not.
</DL>
</P><P>

<A NAME="IDX25"></A>
<DL>
<DT><U>Function:</U> int <B>read_history_range</B> <I>(const char *filename, int from, int to)</I>
<DD>Read a range of lines from <VAR>filename</VAR>, adding them to the history list.
Start reading at line <VAR>from</VAR> and end at <VAR>to</VAR>.
If <VAR>from</VAR> is zero, start at the beginning.  If <VAR>to</VAR> is less than
<VAR>from</VAR>, then read until the end of the file.  If <VAR>filename</VAR> is
<CODE>NULL</CODE>, then read from <TT>`~/.history'</TT>.  Returns 0 if successful,
or <CODE>errno</CODE> if not.
</DL>
</P><P>

<A NAME="IDX26"></A>
<DL>
<DT><U>Function:</U> int <B>write_history</B> <I>(const char *filename)</I>
<DD>Write the current history to <VAR>filename</VAR>, overwriting <VAR>filename</VAR>
if necessary.
If <VAR>filename</VAR> is <CODE>NULL</CODE>, then write the history list to
<TT>`~/.history'</TT>.
Returns 0 on success, or <CODE>errno</CODE> on a read or write error.
</DL>
</P><P>

<A NAME="IDX27"></A>
<DL>
<DT><U>Function:</U> int <B>append_history</B> <I>(int nelements, const char *filename)</I>
<DD>Append the last <VAR>nelements</VAR> of the history list to <VAR>filename</VAR>.
If <VAR>filename</VAR> is <CODE>NULL</CODE>, then append to <TT>`~/.history'</TT>.
Returns 0 on success, or <CODE>errno</CODE> on a read or write error.
</DL>
</P><P>

<A NAME="IDX28"></A>
<DL>
<DT><U>Function:</U> int <B>history_truncate_file</B> <I>(const char *filename, int nlines)</I>
<DD>Truncate the history file <VAR>filename</VAR>, leaving only the last
<VAR>nlines</VAR> lines.
If <VAR>filename</VAR> is <CODE>NULL</CODE>, then <TT>`~/.history'</TT> is truncated.
Returns 0 on success, or <CODE>errno</CODE> on failure.
</DL>
</P><P>

<A NAME="History Expansion"></A>
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<H3> 2.3.7 History Expansion </H3>
<!--docid::SEC16::-->
<P>

These functions implement history expansion.
</P><P>

<A NAME="IDX29"></A>
<DL>
<DT><U>Function:</U> int <B>history_expand</B> <I>(char *string, char **output)</I>
<DD>Expand <VAR>string</VAR>, placing the result into <VAR>output</VAR>, a pointer
to a string (see section <A HREF="history.html#SEC2">1.1 History Expansion</A>).  Returns:
<DL COMPACT>
<DT><CODE>0</CODE>
<DD>If no expansions took place (or, if the only change in
the text was the removal of escape characters preceding the history expansion
character);
<DT><CODE>1</CODE>
<DD>if expansions did take place;
<DT><CODE>-1</CODE>
<DD>if there was an error in expansion;
<DT><CODE>2</CODE>
<DD>if the returned line should be displayed, but not executed,
as with the <CODE>:p</CODE> modifier (see section <A HREF="history.html#SEC5">1.1.3 Modifiers</A>).
</DL>
<P>

If an error ocurred in expansion, then <VAR>output</VAR> contains a descriptive
error message.
</DL>
</P><P>

<A NAME="IDX30"></A>
<DL>
<DT><U>Function:</U> char * <B>get_history_event</B> <I>(const char *string, int *cindex, int qchar)</I>
<DD>Returns the text of the history event beginning at <VAR>string</VAR> +
<VAR>*cindex</VAR>.  <VAR>*cindex</VAR> is modified to point to after the event
specifier.  At function entry, <VAR>cindex</VAR> points to the index into
<VAR>string</VAR> where the history event specification begins.  <VAR>qchar</VAR>
is a character that is allowed to end the event specification in addition
to the "normal" terminating characters.
</DL>
</P><P>

<A NAME="IDX31"></A>
<DL>
<DT><U>Function:</U> char ** <B>history_tokenize</B> <I>(const char *string)</I>
<DD>Return an array of tokens parsed out of <VAR>string</VAR>, much as the
shell might.  The tokens are split on the characters in the
<VAR>history_word_delimiters</VAR> variable,
and shell quoting conventions are obeyed.
</DL>
</P><P>

<A NAME="IDX32"></A>
<DL>
<DT><U>Function:</U> char * <B>history_arg_extract</B> <I>(int first, int last, const char *string)</I>
<DD>Extract a string segment consisting of the <VAR>first</VAR> through <VAR>last</VAR>
arguments present in <VAR>string</VAR>.  Arguments are split using
<CODE>history_tokenize</CODE>.
</DL>
</P><P>

<A NAME="History Variables"></A>
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<H2> 2.4 History Variables </H2>
<!--docid::SEC17::-->
<P>

This section describes the externally-visible variables exported by
the GNU History Library.
</P><P>

<A NAME="IDX33"></A>
<DL>
<DT><U>Variable:</U> int <B>history_base</B>
<DD>The logical offset of the first entry in the history list.
</DL>
</P><P>

<A NAME="IDX34"></A>
<DL>
<DT><U>Variable:</U> int <B>history_length</B>
<DD>The number of entries currently stored in the history list.
</DL>
</P><P>

<A NAME="IDX35"></A>
<DL>
<DT><U>Variable:</U> int <B>history_max_entries</B>
<DD>The maximum number of history entries.  This must be changed using
<CODE>stifle_history()</CODE>.
</DL>
</P><P>

<A NAME="IDX36"></A>
<DL>
<DT><U>Variable:</U> char <B>history_expansion_char</B>
<DD>The character that introduces a history event.  The default is <SAMP>`!'</SAMP>.
Setting this to 0 inhibits history expansion.
</DL>
</P><P>

<A NAME="IDX37"></A>
<DL>
<DT><U>Variable:</U> char <B>history_subst_char</B>
<DD>The character that invokes word substitution if found at the start of
a line.  The default is <SAMP>`^'</SAMP>.
</DL>
</P><P>

<A NAME="IDX38"></A>
<DL>
<DT><U>Variable:</U> char <B>history_comment_char</B>
<DD>During tokenization, if this character is seen as the first character
of a word, then it and all subsequent characters up to a newline are
ignored, suppressing history expansion for the remainder of the line.
This is disabled by default.
</DL>
</P><P>

<A NAME="IDX39"></A>
<DL>
<DT><U>Variable:</U> char * <B>history_word_delimiters</B>
<DD>The characters that separate tokens for <CODE>history_tokenize()</CODE>.
The default value is <CODE>" \t\n()<>;&|"</CODE>.
</DL>
</P><P>

<A NAME="IDX40"></A>
<DL>
<DT><U>Variable:</U> char * <B>history_no_expand_chars</B>
<DD>The list of characters which inhibit history expansion if found immediately
following <VAR>history_expansion_char</VAR>.  The default is space, tab, newline,
carriage return, and <SAMP>`='</SAMP>.
</DL>
</P><P>

<A NAME="IDX41"></A>
<DL>
<DT><U>Variable:</U> char * <B>history_search_delimiter_chars</B>
<DD>The list of additional characters which can delimit a history search
string, in addition to space, TAB, <SAMP>`:'</SAMP> and <SAMP>`?'</SAMP> in the case of
a substring search.  The default is empty.
</DL>
</P><P>

<A NAME="IDX42"></A>
<DL>
<DT><U>Variable:</U> int <B>history_quotes_inhibit_expansion</B>
<DD>If non-zero, single-quoted words are not scanned for the history expansion