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<a name="Conditional-Expressions-1"></a>
<h1 class="chapter">12. Conditional Expressions</h1>
<a name="index-conditional-expressions"></a>
<a name="index-expressions_002c-conditional"></a>
<p>A <em>conditional expression</em> is used with the <tt>[[</tt>
compound command to test attributes of files and to compare strings.
Each expression can be constructed from one or more
of the following unary or binary expressions:
</p>
<dl compact="compact">
<dt> <tt>-a</tt> <var>file</var></dt>
<dd><p>true if <var>file</var> exists.
</p>
</dd>
<dt> <tt>-b</tt> <var>file</var></dt>
<dd><p>true if <var>file</var> exists and is a block special file.
</p>
</dd>
<dt> <tt>-c</tt> <var>file</var></dt>
<dd><p>true if <var>file</var> exists and is a character special file.
</p>
</dd>
<dt> <tt>-d</tt> <var>file</var></dt>
<dd><p>true if <var>file</var> exists and is a directory.
</p>
</dd>
<dt> <tt>-e</tt> <var>file</var></dt>
<dd><p>true if <var>file</var> exists.
</p>
</dd>
<dt> <tt>-f</tt> <var>file</var></dt>
<dd><p>true if <var>file</var> exists and is a regular file.
</p>
</dd>
<dt> <tt>-g</tt> <var>file</var></dt>
<dd><p>true if <var>file</var> exists and has its setgid bit set.
</p>
</dd>
<dt> <tt>-h</tt> <var>file</var></dt>
<dd><p>true if <var>file</var> exists and is a symbolic link.
</p>
</dd>
<dt> <tt>-k</tt> <var>file</var></dt>
<dd><p>true if <var>file</var> exists and has its sticky bit set.
</p>
</dd>
<dt> <tt>-n</tt> <var>string</var></dt>
<dd><p>true if length of <var>string</var> is non-zero.
</p>
</dd>
<dt> <tt>-o</tt> <var>option</var></dt>
<dd><p>true if option named <var>option</var> is on. <var>option</var>
may be a single character, in which case it is a single letter option name.
(See <a href="Options.html#Specifying-Options">Specifying Options</a>.)
</p>
</dd>
<dt> <tt>-p</tt> <var>file</var></dt>
<dd><p>true if <var>file</var> exists and is a FIFO special file (named pipe).
</p>
</dd>
<dt> <tt>-r</tt> <var>file</var></dt>
<dd><p>true if <var>file</var> exists and is readable by current process.
</p>
</dd>
<dt> <tt>-s</tt> <var>file</var></dt>
<dd><p>true if <var>file</var> exists and has size greater than zero.
</p>
</dd>
<dt> <tt>-t</tt> <var>fd</var></dt>
<dd><p>true if file descriptor number <var>fd</var>
is open and associated with a terminal device.
(note: <var>fd</var> is not optional)
</p>
</dd>
<dt> <tt>-u</tt> <var>file</var></dt>
<dd><p>true if <var>file</var> exists and has its setuid bit set.
</p>
</dd>
<dt> <tt>-w</tt> <var>file</var></dt>
<dd><p>true if <var>file</var> exists and is writable by current process.
</p>
</dd>
<dt> <tt>-x</tt> <var>file</var></dt>
<dd><p>true if <var>file</var> exists and is executable by current process.
If <var>file</var> exists and is a directory, then the current process
has permission to search in the directory.
</p>
</dd>
<dt> <tt>-z</tt> <var>string</var></dt>
<dd><p>true if length of <var>string</var> is zero.
</p>
</dd>
<dt> <tt>-L</tt> <var>file</var></dt>
<dd><p>true if <var>file</var> exists and is a symbolic link.
</p>
</dd>
<dt> <tt>-O</tt> <var>file</var></dt>
<dd><p>true if <var>file</var> exists and is owned by the effective user ID of this process.
</p>
</dd>
<dt> <tt>-G</tt> <var>file</var></dt>
<dd><p>true if <var>file</var> exists and its group matches
the effective group ID of this process.
</p>
</dd>
<dt> <tt>-S</tt> <var>file</var></dt>
<dd><p>true if <var>file</var> exists and is a socket.
</p>
</dd>
<dt> <tt>-N</tt> <var>file</var></dt>
<dd><p>true if <var>file</var> exists and its access time is
not newer than its modification time.
</p>
</dd>
<dt> <var>file1</var> <tt>-nt</tt> <var>file2</var></dt>
<dd><p>true if <var>file1</var> exists and is newer than <var>file2</var>.
</p>
</dd>
<dt> <var>file1</var> <tt>-ot</tt> <var>file2</var></dt>
<dd><p>true if <var>file1</var> exists and is older than <var>file2</var>.
</p>
</dd>
<dt> <var>file1</var> <tt>-ef</tt> <var>file2</var></dt>
<dd><p>true if <var>file1</var> and <var>file2</var> exist and refer to the same file.
</p>
</dd>
<dt> <var>string</var> <tt>=</tt> <var>pattern</var></dt>
<dt> <var>string</var> <tt>==</tt> <var>pattern</var></dt>
<dd><p>true if <var>string</var> matches <var>pattern</var>.
The ‘<tt>==</tt>’ form is the preferred one. The ‘<tt>=</tt>’ form is for
backward compatibility and should be considered obsolete.
</p>
</dd>
<dt> <var>string</var> <tt>!=</tt> <var>pattern</var></dt>
<dd><p>true if <var>string</var> does not match <var>pattern</var>.
</p>
</dd>
<dt> <var>string</var> <tt>=~</tt> <var>regexp</var></dt>
<dd><p>true if <var>string</var> matches the regular expression
<var>regexp</var>. If the option <tt>RE_MATCH_PCRE</tt> is set
<var>regexp</var> is tested as a PCRE regular expression using
the <tt>zsh/pcre</tt> module, else it is tested as a POSIX
extended regular expression using the <tt>zsh/regex</tt> module.
Upon successful match, some variables will be updated; no variables
are changed if the matching fails.
</p>
<p>If the option <tt>BASH_REMATCH</tt> is not set the scalar parameter
<tt>MATCH</tt> is set to the substring that matched the pattern and
the integer parameters <tt>MBEGIN</tt> and <tt>MEND</tt> to the index of the start
and end, respectively, of the match in <var>string</var>, such that if
<var>string</var> is contained in variable <tt>var</tt> the expression
‘${var[$MBEGIN,$MEND]}’ is identical to ‘$MATCH’. The setting
of the option <tt>KSH_ARRAYS</tt> is respected. Likewise, the array
<tt>match</tt> is set to the substrings that matched parenthesised
subexpressions and the arrays <tt>mbegin</tt> and <tt>mend</tt> to the indices of
the start and end positions, respectively, of the substrings within
<var>string</var>. The arrays are not set if there were no parenthesised
subexpresssions. For example, if the string ‘<tt>a short string</tt>’ is matched
against the regular expression ‘<tt>s(...)t</tt>’, then (assuming the
option <tt>KSH_ARRAYS</tt> is not set) <tt>MATCH</tt>, <tt>MBEGIN</tt>
and <tt>MEND</tt> are ‘<tt>short</tt>’, 3 and 7, respectively, while <tt>match</tt>,
<tt>mbegin</tt> and <tt>mend</tt> are single entry arrays containing
the strings ‘<tt>hor</tt>’, ‘<tt>4</tt>’ and ‘<tt>6</tt>, respectively.
</p>
<p>If the option <tt>BASH_REMATCH</tt> is set the array
<tt>BASH_REMATCH</tt> is set to the substring that matched the pattern
followed by the substrings that matched parenthesised
subexpressions within the pattern.
</p>
</dd>
<dt> <var>string1</var> <tt><</tt> <var>string2</var></dt>
<dd><p>true if <var>string1</var> comes before <var>string2</var>
based on ASCII value of their characters.
</p>
</dd>
<dt> <var>string1</var> <tt>></tt> <var>string2</var></dt>
<dd><p>true if <var>string1</var> comes after <var>string2</var>
based on ASCII value of their characters.
</p>
</dd>
<dt> <var>exp1</var> <tt>-eq</tt> <var>exp2</var></dt>
<dd><p>true if <var>exp1</var> is numerically equal to <var>exp2</var>.
Note that for purely numeric comparisons use of the
<tt>((</tt><var>...</var><tt>))</tt> builtin described in
<a href="Arithmetic-Evaluation.html#Arithmetic-Evaluation">Arithmetic Evaluation</a> is more convenient than
conditional expressions.
</p>
</dd>
<dt> <var>exp1</var> <tt>-ne</tt> <var>exp2</var></dt>
<dd><p>true if <var>exp1</var> is numerically not equal to <var>exp2</var>.
</p>
</dd>
<dt> <var>exp1</var> <tt>-lt</tt> <var>exp2</var></dt>
<dd><p>true if <var>exp1</var> is numerically less than <var>exp2</var>.
</p>
</dd>
<dt> <var>exp1</var> <tt>-gt</tt> <var>exp2</var></dt>
<dd><p>true if <var>exp1</var> is numerically greater than <var>exp2</var>.
</p>
</dd>
<dt> <var>exp1</var> <tt>-le</tt> <var>exp2</var></dt>
<dd><p>true if <var>exp1</var> is numerically less than or equal to <var>exp2</var>.
</p>
</dd>
<dt> <var>exp1</var> <tt>-ge</tt> <var>exp2</var></dt>
<dd><p>true if <var>exp1</var> is numerically greater than or equal to <var>exp2</var>.
</p>
</dd>
<dt> <tt>(</tt> <var>exp</var> <tt>)</tt></dt>
<dd><p>true if <var>exp</var> is true.
</p>
</dd>
<dt> <tt>!</tt> <var>exp</var></dt>
<dd><p>true if <var>exp</var> is false.
</p>
</dd>
<dt> <var>exp1</var> <tt>&&</tt> <var>exp2</var></dt>
<dd><p>true if <var>exp1</var> and <var>exp2</var> are both true.
</p>
</dd>
<dt> <var>exp1</var> <tt>||</tt> <var>exp2</var></dt>
<dd><p>true if either <var>exp1</var> or <var>exp2</var> is true.
</p>
</dd>
</dl>
<p>Normal shell expansion is performed on the <var>file</var>, <var>string</var> and
<var>pattern</var> arguments, but the result of each expansion is constrained to
be a single word, similar to the effect of double quotes.
Filename generation is not performed on any form of argument to conditions.
However, pattern metacharacters are active for the <var>pattern</var> arguments;
the patterns are the same as those used for filename generation, see
<a href="Expansion.html#Filename-Generation">Filename Generation</a>, but there is no special behaviour
of ‘<tt>/</tt>’ nor initial dots, and no glob qualifiers are allowed.
</p>
<p>In each of the above expressions, if
<var>file</var> is of the form ‘<tt>/dev/fd/</tt><var>n</var>’,
where <var>n</var> is an integer,
then the test applied to the open file whose
descriptor number is <var>n</var>,
even if the underlying system does not support
the <tt>/dev/fd</tt> directory.
</p>
<p>In the forms which do numeric comparison, the expressions <var>exp</var>
undergo arithmetic expansion as if they were enclosed in <tt>$((...))</tt>.
</p>
<p>For example, the following:
</p>
<table><tr><td> </td><td><pre class="example">[[ ( -f foo || -f bar ) && $report = y* ]] && print File exists.
</pre></td></tr></table>
<p>tests if either file <tt>foo</tt> or file <tt>bar</tt> exists, and if so, if the
value of the parameter <tt>report</tt> begins with ‘<tt>y</tt>’; if the complete
condition is true, the message ‘<tt>File exists.</tt>’ is printed.
</p><hr size="6">
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