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<div class="subsection" id="Searching-and-Replacing-in-Strings">
<div class="header">
<p>
Previous: <a href="Searching-in-Strings.html" accesskey="p" rel="prev">Searching in Strings</a>, Up: <a href="String-Operations.html" accesskey="u" rel="up">String Operations</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
</div>
<hr>
<span id="Searching-and-Replacing-in-Strings-1"></span><h4 class="subsection">5.3.5 Searching and Replacing in Strings</h4>
<span id="XREFstrrep"></span><dl class="def">
<dt id="index-strrep"><span class="category">: </span><span><em><var>newstr</var> =</em> <strong>strrep</strong> <em>(<var>str</var>, <var>ptn</var>, <var>rep</var>)</em><a href='#index-strrep' class='copiable-anchor'> ¶</a></span></dt>
<dt id="index-strrep-1"><span class="category">: </span><span><em><var>newstr</var> =</em> <strong>strrep</strong> <em>(<var>cellstr</var>, <var>ptn</var>, <var>rep</var>)</em><a href='#index-strrep-1' class='copiable-anchor'> ¶</a></span></dt>
<dt id="index-strrep-2"><span class="category">: </span><span><em><var>newstr</var> =</em> <strong>strrep</strong> <em>(…, "overlaps", <var>val</var>)</em><a href='#index-strrep-2' class='copiable-anchor'> ¶</a></span></dt>
<dd><p>Replace all occurrences of the pattern <var>ptn</var> in the string <var>str</var>
with the string <var>rep</var> and return the result.
</p>
<p>The optional argument <code>"overlaps"</code> determines whether the pattern
can match at every position in <var>str</var> (true), or only for unique
occurrences of the complete pattern (false). The default is true.
</p>
<p><var>s</var> may also be a cell array of strings, in which case the replacement
is done for each element and a cell array is returned.
</p>
<p>Example:
</p>
<div class="example">
<pre class="example">strrep ("This is a test string", "is", "&%$")
⇒ "Th&%$ &%$ a test string"
</pre></div>
<p><strong>See also:</strong> <a href="#XREFregexprep">regexprep</a>, <a href="Searching-in-Strings.html#XREFstrfind">strfind</a>.
</p></dd></dl>
<span id="XREFerase"></span><dl class="def">
<dt id="index-erase"><span class="category">: </span><span><em><var>newstr</var> =</em> <strong>erase</strong> <em>(<var>str</var>, <var>ptn</var>)</em><a href='#index-erase' class='copiable-anchor'> ¶</a></span></dt>
<dd><p>Delete all occurrences of <var>ptn</var> within <var>str</var>.
</p>
<p><var>str</var> and <var>ptn</var> can be ordinary strings, cell array of strings, or
character arrays.
</p>
<p>Examples
</p>
<div class="example">
<pre class="example">## string, single pattern
erase ("Hello World!", " World")
⇒ "Hello!"
## cellstr, single pattern
erase ({"Hello", "World!"}, "World")
⇒ {"Hello", "!"}
## string, multiple patterns
erase ("The Octave interpreter is fabulous", ...
{"interpreter ", "The "})
⇒ "Octave is fabulous"
## cellstr, multiple patterns
erase ({"The ", "Octave interpreter ", "is fabulous"}, ...
{"interpreter ", "The "})
⇒ {"", "Octave ", "is fabulous"}
</pre></div>
<p>Programming Note: <code>erase</code> deletes the first instance of a pattern in a
string when there are overlapping occurrences. For example:
</p>
<div class="example">
<pre class="example">erase ("abababa", "aba")
⇒ "b"
</pre></div>
<p>For processing overlaps, see <a href="#XREFstrrep"><code>strrep</code></a>.
</p>
<p><strong>See also:</strong> <a href="#XREFstrrep">strrep</a>, <a href="#XREFregexprep">regexprep</a>.
</p></dd></dl>
<span id="XREFregexp"></span><dl class="def">
<dt id="index-regexp"><span class="category">: </span><span><em>[<var>s</var>, <var>e</var>, <var>te</var>, <var>m</var>, <var>t</var>, <var>nm</var>, <var>sp</var>] =</em> <strong>regexp</strong> <em>(<var>str</var>, <var>pat</var>)</em><a href='#index-regexp' class='copiable-anchor'> ¶</a></span></dt>
<dt id="index-regexp-1"><span class="category">: </span><span><em>[…] =</em> <strong>regexp</strong> <em>(<var>str</var>, <var>pat</var>, "<var>opt1</var>", …)</em><a href='#index-regexp-1' class='copiable-anchor'> ¶</a></span></dt>
<dd><p>Regular expression string matching.
</p>
<p>Search for <var>pat</var> in UTF-8 encoded <var>str</var> and return the positions and
substrings of any matches, or empty values if there are none.
</p>
<p>The matched pattern <var>pat</var> can include any of the standard regex
operators, including:
</p>
<dl compact="compact">
<dt><span><code>.</code></span></dt>
<dd><p>Match any character
</p>
</dd>
<dt><span><code>* + ? {}</code></span></dt>
<dd><p>Repetition operators, representing
</p>
<dl compact="compact">
<dt><span><code>*</code></span></dt>
<dd><p>Match zero or more times
</p>
</dd>
<dt><span><code>+</code></span></dt>
<dd><p>Match one or more times
</p>
</dd>
<dt><span><code>?</code></span></dt>
<dd><p>Match zero or one times
</p>
</dd>
<dt><span><code>{<var>n</var>}</code></span></dt>
<dd><p>Match exactly <var>n</var> times
</p>
</dd>
<dt><span><code>{<var>n</var>,}</code></span></dt>
<dd><p>Match <var>n</var> or more times
</p>
</dd>
<dt><span><code>{<var>m</var>,<var>n</var>}</code></span></dt>
<dd><p>Match between <var>m</var> and <var>n</var> times
</p></dd>
</dl>
</dd>
<dt><span><code>[…] [^…]</code></span></dt>
<dd>
<p>List operators. The pattern will match any character listed between
<code>"["</code> and <code>"]"</code>. If the first character is <code>"^"</code> then the
pattern is inverted and any character except those listed between brackets
will match.
</p>
<p>Escape sequences defined below can also be used inside list operators. For
example, a template for a floating point number might be <code>[-+.\d]+</code>.
</p>
</dd>
<dt><span><code>() (?:)</code></span></dt>
<dd><p>Grouping operator. The first form, parentheses only, also creates a token.
</p>
</dd>
<dt><span><code>|</code></span></dt>
<dd><p>Alternation operator. Match one of a choice of regular expressions. The
alternatives must be delimited by the grouping operator <code>()</code> above.
</p>
</dd>
<dt><span><code>^ $</code></span></dt>
<dd><p>Anchoring operators. Requires pattern to occur at the start (<code>^</code>) or
end (<code>$</code>) of the string.
</p></dd>
</dl>
<p>In addition, the following escaped characters have special meaning.
</p>
<dl compact="compact">
<dt><span><code>\d</code></span></dt>
<dd><p>Match any digit
</p>
</dd>
<dt><span><code>\D</code></span></dt>
<dd><p>Match any non-digit
</p>
</dd>
<dt><span><code>\s</code></span></dt>
<dd><p>Match any whitespace character
</p>
</dd>
<dt><span><code>\S</code></span></dt>
<dd><p>Match any non-whitespace character
</p>
</dd>
<dt><span><code>\w</code></span></dt>
<dd><p>Match any word character
</p>
</dd>
<dt><span><code>\W</code></span></dt>
<dd><p>Match any non-word character
</p>
</dd>
<dt><span><code>\<</code></span></dt>
<dd><p>Match the beginning of a word
</p>
</dd>
<dt><span><code>\></code></span></dt>
<dd><p>Match the end of a word
</p>
</dd>
<dt><span><code>\B</code></span></dt>
<dd><p>Match within a word
</p></dd>
</dl>
<p>Implementation Note: For compatibility with <small>MATLAB</small>, escape sequences
in <var>pat</var> (e.g., <code>"\n"</code> => newline) are expanded
even when <var>pat</var> has been defined with single quotes. To disable
expansion use a second backslash before the escape sequence (e.g.,
"\\n") or use the <code>regexptranslate</code>
function.
</p>
<p>The outputs of <code>regexp</code> default to the order given below
</p>
<dl compact="compact">
<dt><span><var>s</var></span></dt>
<dd><p>The start indices of each matching substring
</p>
</dd>
<dt><span><var>e</var></span></dt>
<dd><p>The end indices of each matching substring
</p>
</dd>
<dt><span><var>te</var></span></dt>
<dd><p>The extents of each matched token surrounded by <code>(…)</code> in
<var>pat</var>
</p>
</dd>
<dt><span><var>m</var></span></dt>
<dd><p>A cell array of the text of each match
</p>
</dd>
<dt><span><var>t</var></span></dt>
<dd><p>A cell array of the text of each token matched
</p>
</dd>
<dt><span><var>nm</var></span></dt>
<dd><p>A structure containing the text of each matched named token, with the name
being used as the fieldname. A named token is denoted by
<code>(?<name>…)</code>.
</p>
</dd>
<dt><span><var>sp</var></span></dt>
<dd><p>A cell array of the text not returned by match, i.e., what remains if you
split the string based on <var>pat</var>.
</p></dd>
</dl>
<p>Particular output arguments, or the order of the output arguments, can be
selected by additional <var>opt</var> arguments. These are strings and the
correspondence between the output arguments and the optional argument
are
</p>
<table>
<tr><td width="20%"></td><td width="30%"><code>'start'</code></td><td width="30%"><var>s</var></td><td width="20%"></td></tr>
<tr><td width="20%"></td><td width="30%"><code>'end'</code></td><td width="30%"><var>e</var></td><td width="20%"></td></tr>
<tr><td width="20%"></td><td width="30%"><code>'tokenExtents'</code></td><td width="30%"><var>te</var></td><td width="20%"></td></tr>
<tr><td width="20%"></td><td width="30%"><code>'match'</code></td><td width="30%"><var>m</var></td><td width="20%"></td></tr>
<tr><td width="20%"></td><td width="30%"><code>'tokens'</code></td><td width="30%"><var>t</var></td><td width="20%"></td></tr>
<tr><td width="20%"></td><td width="30%"><code>'names'</code></td><td width="30%"><var>nm</var></td><td width="20%"></td></tr>
<tr><td width="20%"></td><td width="30%"><code>'split'</code></td><td width="30%"><var>sp</var></td><td width="20%"></td></tr>
</table>
<p>Additional arguments are summarized below.
</p>
<dl compact="compact">
<dt><span>‘<samp>once</samp>’</span></dt>
<dd><p>Return only the first occurrence of the pattern.
</p>
</dd>
<dt><span>‘<samp>matchcase</samp>’</span></dt>
<dd><p>Make the matching case sensitive. (default)
</p>
<p>Alternatively, use (?-i) in the pattern.
</p>
</dd>
<dt><span>‘<samp>ignorecase</samp>’</span></dt>
<dd><p>Ignore case when matching the pattern to the string.
</p>
<p>Alternatively, use (?i) in the pattern.
</p>
</dd>
<dt><span>‘<samp>stringanchors</samp>’</span></dt>
<dd><p>Match the anchor characters at the beginning and end of the string.
(default)
</p>
<p>Alternatively, use (?-m) in the pattern.
</p>
</dd>
<dt><span>‘<samp>lineanchors</samp>’</span></dt>
<dd><p>Match the anchor characters at the beginning and end of the line.
</p>
<p>Alternatively, use (?m) in the pattern.
</p>
</dd>
<dt><span>‘<samp>dotall</samp>’</span></dt>
<dd><p>The pattern <code>.</code> matches all characters including the newline character.
(default)
</p>
<p>Alternatively, use (?s) in the pattern.
</p>
</dd>
<dt><span>‘<samp>dotexceptnewline</samp>’</span></dt>
<dd><p>The pattern <code>.</code> matches all characters except the newline character.
</p>
<p>Alternatively, use (?-s) in the pattern.
</p>
</dd>
<dt><span>‘<samp>literalspacing</samp>’</span></dt>
<dd><p>All characters in the pattern, including whitespace, are significant and are
used in pattern matching. (default)
</p>
<p>Alternatively, use (?-x) in the pattern.
</p>
</dd>
<dt><span>‘<samp>freespacing</samp>’</span></dt>
<dd><p>The pattern may include arbitrary whitespace and also comments beginning
with the character ‘<samp>#</samp>’.
</p>
<p>Alternatively, use (?x) in the pattern.
</p>
</dd>
<dt><span>‘<samp>noemptymatch</samp>’</span></dt>
<dd><p>Zero-length matches are not returned. (default)
</p>
</dd>
<dt><span>‘<samp>emptymatch</samp>’</span></dt>
<dd><p>Return zero-length matches.
</p>
<p><code>regexp ('a', 'b*', 'emptymatch')</code> returns <code>[1 2]</code> because there
are zero or more <code>'b'</code> characters at positions 1 and end-of-string.
</p>
</dd>
</dl>
<p>Stack Limitation Note: Pattern searches are done with a recursive function
which can overflow the program stack when there are a high number of matches.
For example,
</p>
<div class="example">
<pre class="example"><code>regexp (repmat ('a', 1, 1e5), '(a)+')</code>
</pre></div>
<p>may lead to a segfault. As an alternative, consider constructing pattern
searches that reduce the number of matches (e.g., by creatively using set
complement), and then further processing the return variables (now reduced in
size) with successive <code>regexp</code> searches.
</p>
<p><strong>See also:</strong> <a href="#XREFregexpi">regexpi</a>, <a href="Searching-in-Strings.html#XREFstrfind">strfind</a>, <a href="#XREFregexprep">regexprep</a>.
</p></dd></dl>
<span id="XREFregexpi"></span><dl class="def">
<dt id="index-regexpi"><span class="category">: </span><span><em>[<var>s</var>, <var>e</var>, <var>te</var>, <var>m</var>, <var>t</var>, <var>nm</var>, <var>sp</var>] =</em> <strong>regexpi</strong> <em>(<var>str</var>, <var>pat</var>)</em><a href='#index-regexpi' class='copiable-anchor'> ¶</a></span></dt>
<dt id="index-regexpi-1"><span class="category">: </span><span><em>[…] =</em> <strong>regexpi</strong> <em>(<var>str</var>, <var>pat</var>, "<var>opt1</var>", …)</em><a href='#index-regexpi-1' class='copiable-anchor'> ¶</a></span></dt>
<dd>
<p>Case insensitive regular expression string matching.
</p>
<p>Search for <var>pat</var> in UTF-8 encoded <var>str</var> and return the positions and
substrings of any matches, or empty values if there are none.
See <a href="#XREFregexp"><code>regexp</code></a>, for details on the syntax of the search
pattern.
</p>
<p><strong>See also:</strong> <a href="#XREFregexp">regexp</a>.
</p></dd></dl>
<span id="XREFregexprep"></span><dl class="def">
<dt id="index-regexprep"><span class="category">: </span><span><em><var>outstr</var> =</em> <strong>regexprep</strong> <em>(<var>string</var>, <var>pat</var>, <var>repstr</var>)</em><a href='#index-regexprep' class='copiable-anchor'> ¶</a></span></dt>
<dt id="index-regexprep-1"><span class="category">: </span><span><em><var>outstr</var> =</em> <strong>regexprep</strong> <em>(<var>string</var>, <var>pat</var>, <var>repstr</var>, "<var>opt1</var>", …)</em><a href='#index-regexprep-1' class='copiable-anchor'> ¶</a></span></dt>
<dd><p>Replace occurrences of pattern <var>pat</var> in <var>string</var> with <var>repstr</var>.
</p>
<p>The pattern is a regular expression as documented for <code>regexp</code>.
See <a href="#XREFregexp"><code>regexp</code></a>.
</p>
<p>All strings must be UTF-8 encoded.
</p>
<p>The replacement string may contain <code>$i</code>, which substitutes for the ith
set of parentheses in the match string. For example,
</p>
<div class="example">
<pre class="example">regexprep ("Bill Dunn", '(\w+) (\w+)', '$2, $1')
</pre></div>
<p>returns <code>"Dunn, Bill"</code>
</p>
<p>Options in addition to those of <code>regexp</code> are
</p>
<dl compact="compact">
<dt><span>‘<samp>once</samp>’</span></dt>
<dd><p>Replace only the first occurrence of <var>pat</var> in the result.
</p>
</dd>
<dt><span>‘<samp>warnings</samp>’</span></dt>
<dd><p>This option is present for compatibility but is ignored.
</p>
</dd>
</dl>
<p>Implementation Note: For compatibility with <small>MATLAB</small>, escape sequences
in <var>pat</var> (e.g., <code>"\n"</code> => newline) are expanded
even when <var>pat</var> has been defined with single quotes. To disable
expansion use a second backslash before the escape sequence (e.g.,
"\\n") or use the <code>regexptranslate</code>
function.
</p>
<p><strong>See also:</strong> <a href="#XREFregexp">regexp</a>, <a href="#XREFregexpi">regexpi</a>, <a href="#XREFstrrep">strrep</a>.
</p></dd></dl>
<span id="XREFregexptranslate"></span><dl class="def">
<dt id="index-regexptranslate"><span class="category">: </span><span><em></em> <strong>regexptranslate</strong> <em>(<var>op</var>, <var>s</var>)</em><a href='#index-regexptranslate' class='copiable-anchor'> ¶</a></span></dt>
<dd><p>Translate a string for use in a regular expression.
</p>
<p>This may include either wildcard replacement or special character escaping.
</p>
<p>The behavior is controlled by <var>op</var> which can take the following
values
</p>
<dl compact="compact">
<dt><span><code>"wildcard"</code></span></dt>
<dd><p>The wildcard characters <code>.</code>, <code>*</code>, and <code>?</code> are replaced with
wildcards that are appropriate for a regular expression. For example:
</p>
<div class="example">
<pre class="example">regexptranslate ("wildcard", "*.m")
⇒ '.*\.m'
</pre></div>
</dd>
<dt><span><code>"escape"</code></span></dt>
<dd><p>The characters <code>$.?[]</code>, that have special meaning for regular
expressions are escaped so that they are treated literally. For example:
</p>
<div class="example">
<pre class="example">regexptranslate ("escape", "12.5")
⇒ '12\.5'
</pre></div>
</dd>
</dl>
<p><strong>See also:</strong> <a href="#XREFregexp">regexp</a>, <a href="#XREFregexpi">regexpi</a>, <a href="#XREFregexprep">regexprep</a>.
</p></dd></dl>
</div>
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