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<center><font size="2">The Open Group Base Specifications Issue 6<br>
IEEE Std 1003.1-2001<br>
Copyright &copy; 2001 The IEEE and The Open Group, All Rights reserved.</font></center>
<!--header end-->
<hr size="2" noshade>
<h4><a name="tag_04_54_01"></a>NAME</h4>
<blockquote>file - determine file type</blockquote>
<h4><a name="tag_04_54_02"></a>SYNOPSIS</h4>
<blockquote class="synopsis">
<div class="box"><code><tt><sup>[<a href="javascript:open_code('UP')">UP</a>]</sup> <img src="../images/opt-start.gif" alt=
"[Option Start]" border="0"> file</tt> <b>[</b><tt>-dhi</tt><b>][</b><tt>-M</tt> <i>file</i><b>][</b><tt>-m</tt>
<i>file</i><b>]</b> <i>file</i> <tt>... <img src="../images/opt-end.gif" alt="[Option End]" border="0"></tt></code></div>
</blockquote>
<h4><a name="tag_04_54_03"></a>DESCRIPTION</h4>
<blockquote>
<p>The <i>file</i> utility shall perform a series of tests on each specified <i>file</i> in an attempt to classify it:</p>
<ol>
<li>
<p>If the file is not a regular file, its file type shall be identified. The file types directory, FIFO, socket, block special, and
character special shall be identified as such. Other implementation-defined file types may also be identified.</p>
</li>
<li>
<p>If the file is a regular file, and:</p>
<ol type="a">
<li>
<p>The file is zero-length, it shall be identified as an empty file.</p>
</li>
<li>
<p>The file is not zero-length, <i>file</i> shall examine an initial segment of the file and shall make a guess at identifying its
contents or whether it is an executable binary file. (The answer is not guaranteed to be correct.)</p>
</li>
</ol>
</li>
</ol>
<p>If <i>file</i> does not exist, cannot be read, or its file status could not be determined, the output shall indicate that the
file was processed, but that its type could not be determined.</p>
<p>If <i>file</i> is a symbolic link, by default the link shall be resolved and <i>file</i> shall test the type of file referenced
by the symbolic link.</p>
</blockquote>
<h4><a name="tag_04_54_04"></a>OPTIONS</h4>
<blockquote>
<p>The <i>file</i> utility shall conform to the Base Definitions volume of IEEE&nbsp;Std&nbsp;1003.1-2001, <a href=
"../basedefs/xbd_chap12.html#tag_12_02">Section 12.2, Utility Syntax Guidelines</a>.</p>
<p>The following options shall be supported by the implementation:</p>
<dl compact>
<dt><b>-d</b></dt>
<dd>Apply any default system tests to the file.</dd>
<dt><b>-h</b></dt>
<dd>When a symbolic link is encountered, identify the file as a symbolic link. If <b>-h</b> is not specified and <i>file</i> is a
symbolic link that refers to a nonexistent file, <i>file</i> shall identify the file as a symbolic link, as if <b>-h</b> had been
specified.</dd>
<dt><b>-i</b></dt>
<dd>If a file is a regular file, do not attempt to classify the type of the file further, but identify the file as specified in the
STDOUT section, using a &lt;<i>type</i>&gt; string that contains the string <tt>"regular file"</tt> .</dd>
<dt><b>-M&nbsp;</b> <i>file</i></dt>
<dd>Specify the name of a file containing tests that shall be applied to a file in order to classify it (see the EXTENDED
DESCRIPTION). No default system tests shall be applied.</dd>
<dt><b>-m&nbsp;</b> <i>file</i></dt>
<dd>Specify the name of a file containing tests that shall be applied to a file in order to classify it (see the EXTENDED
DESCRIPTION).</dd>
</dl>
<p>If multiple instances of the <b>-m</b>, <b>-d</b>, or <b>-M</b> options are specified, the concatenation of the tests specified,
in the order specified, shall be the set of tests that are applied. If a <b>-M</b> option is specified, no tests other than those
specified using the <b>-d</b>, <b>-M</b>, and <b>-m</b> options shall be applied to the file. If neither the <b>-d</b> nor
<b>-M</b> options are specified, any default system tests shall be applied after any tests specified using the <b>-m</b>
option.</p>
</blockquote>
<h4><a name="tag_04_54_05"></a>OPERANDS</h4>
<blockquote>
<p>The following operand shall be supported:</p>
<dl compact>
<dt><i>file</i></dt>
<dd>A pathname of a file to be tested.</dd>
</dl>
</blockquote>
<h4><a name="tag_04_54_06"></a>STDIN</h4>
<blockquote>
<p>Not used.</p>
</blockquote>
<h4><a name="tag_04_54_07"></a>INPUT FILES</h4>
<blockquote>
<p>The <i>file</i> can be any file type.</p>
</blockquote>
<h4><a name="tag_04_54_08"></a>ENVIRONMENT VARIABLES</h4>
<blockquote>
<p>The following environment variables shall affect the execution of <i>file</i>:</p>
<dl compact>
<dt><i>LANG</i></dt>
<dd>Provide a default value for the internationalization variables that are unset or null. (See the Base Definitions volume of
IEEE&nbsp;Std&nbsp;1003.1-2001, <a href="../basedefs/xbd_chap08.html#tag_08_02">Section 8.2, Internationalization Variables</a> for
the precedence of internationalization variables used to determine the values of locale categories.)</dd>
<dt><i>LC_ALL</i></dt>
<dd>If set to a non-empty string value, override the values of all the other internationalization variables.</dd>
<dt><i>LC_CTYPE</i></dt>
<dd>Determine the locale for the interpretation of sequences of bytes of text data as characters (for example, single-byte as
opposed to multi-byte characters in arguments and input files).</dd>
<dt><i>LC_MESSAGES</i></dt>
<dd>Determine the locale that should be used to affect the format and contents of diagnostic messages written to standard error and
informative messages written to standard output.</dd>
<dt><i>NLSPATH</i></dt>
<dd><sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
Determine the location of message catalogs for the processing of <i>LC_MESSAGES .</i> <img src="../images/opt-end.gif" alt=
"[Option End]" border="0"></dd>
</dl>
</blockquote>
<h4><a name="tag_04_54_09"></a>ASYNCHRONOUS EVENTS</h4>
<blockquote>
<p>Default.</p>
</blockquote>
<h4><a name="tag_04_54_10"></a>STDOUT</h4>
<blockquote>
<p>In the POSIX locale, the following format shall be used to identify each operand, <i>file</i> specified:</p>
<pre>
<tt>"%s: %s\n", &lt;</tt><i>file</i><tt>&gt;, &lt;</tt><i>type</i><tt>&gt;
</tt>
</pre>
<p>The values for &lt;<i>type</i>&gt; are unspecified, except that in the POSIX locale, if <i>file</i> is identified as one of the
types listed in the following table, &lt;<i>type</i>&gt; shall contain (but is not limited to) the corresponding string. Each space
shown in the strings shall be exactly one &lt;space&gt;.<br>
</p>
<center><b><a name="tagtcjh_14"></a> Table: File Utility Output Strings</b></center>
<center>
<table border="1" cellpadding="3" align="center">
<tr valign="top">
<th align="center">
<p class="tent"><b>If <i>file</i> is a:</b></p>
</th>
<th align="center">
<p class="tent"><b>&lt;<i>type</i>&gt; shall contain the string:</b></p>
</th>
</tr>
<tr valign="top">
<td align="left">
<p class="tent">Directory</p>
</td>
<td align="left">
<p class="tent">directory</p>
</td>
</tr>
<tr valign="top">
<td align="left">
<p class="tent">FIFO</p>
</td>
<td align="left">
<p class="tent">fifo</p>
</td>
</tr>
<tr valign="top">
<td align="left">
<p class="tent">Socket</p>
</td>
<td align="left">
<p class="tent">socket</p>
</td>
</tr>
<tr valign="top">
<td align="left">
<p class="tent">Block special</p>
</td>
<td align="left">
<p class="tent">block special</p>
</td>
</tr>
<tr valign="top">
<td align="left">
<p class="tent">Character special</p>
</td>
<td align="left">
<p class="tent">character special</p>
</td>
</tr>
<tr valign="top">
<td align="left">
<p class="tent">Executable binary</p>
</td>
<td align="left">
<p class="tent">executable</p>
</td>
</tr>
<tr valign="top">
<td align="left">
<p class="tent">Empty regular file</p>
</td>
<td align="left">
<p class="tent">empty</p>
</td>
</tr>
<tr valign="top">
<td align="left">
<p class="tent">Symbolic link</p>
</td>
<td align="left">
<p class="tent">symbolic link to</p>
</td>
</tr>
<tr valign="top">
<td align="left">
<p class="tent"><i>ar</i> archive library (see <i>ar</i>)</p>
</td>
<td align="left">
<p class="tent">archive</p>
</td>
</tr>
<tr valign="top">
<td align="left">
<p class="tent">Extended <i>cpio</i> format (see <i>pax</i>)</p>
</td>
<td align="left">
<p class="tent">cpio archive</p>
</td>
</tr>
<tr valign="top">
<td align="left">
<p class="tent">Extended <i>tar</i> format (see <b>ustar</b> in <i>pax</i>)</p>
</td>
<td align="left">
<p class="tent">tar archive</p>
</td>
</tr>
<tr valign="top">
<td align="left">
<p class="tent">Shell script</p>
</td>
<td align="left">
<p class="tent">commands text</p>
</td>
</tr>
<tr valign="top">
<td align="left">
<p class="tent">C-language source</p>
</td>
<td align="left">
<p class="tent">c program text</p>
</td>
</tr>
<tr valign="top">
<td align="left">
<p class="tent">FORTRAN source</p>
</td>
<td align="left">
<p class="tent">fortran program text</p>
</td>
</tr>
</table>
</center>
<p>If <i>file</i> is identified as a symbolic link (see <b>-h</b>), the following alternative output format shall be used:</p>
<pre>
<tt>"%s: %s %s\n", &lt;</tt><i>file</i><tt>&gt;, &lt;</tt><i>type</i><tt>&gt;, &lt;</tt><i>contents of link</i><tt>&gt;"
</tt>
</pre>
<p>If the file named by the <i>file</i> operand does not exist or cannot be read, the string <tt>"cannot open"</tt> shall be
included as part of the &lt;<i>type</i>&gt; field, but this shall not be considered an error that affects the exit status. If the
type of the file named by the <i>file</i> operand cannot be determined, the string <tt>"data"</tt> shall be included as part of the
&lt;<i>type</i>&gt; field, but this shall not be considered an error that affects the exit status.</p>
</blockquote>
<h4><a name="tag_04_54_11"></a>STDERR</h4>
<blockquote>
<p>The standard error shall be used only for diagnostic messages.</p>
</blockquote>
<h4><a name="tag_04_54_12"></a>OUTPUT FILES</h4>
<blockquote>
<p>None.</p>
</blockquote>
<h4><a name="tag_04_54_13"></a>EXTENDED DESCRIPTION</h4>
<blockquote>
<p>A file specified as an option-argument to the <b>-m</b> or <b>-M</b> options shall contain one test per line, which shall be
applied to the file. If the test succeeds, the message field of the line shall be printed and no further tests shall be applied,
with the exception that tests on immediately following lines beginning with a single <tt>'&gt;'</tt> character shall be
applied.</p>
<p>Each line shall be composed of the following four &lt;blank&gt;-separated fields:</p>
<dl compact>
<dt><i>offset</i></dt>
<dd>An unsigned number (optionally preceded by a single <tt>'&gt;'</tt> character) specifying the <i>offset</i>, in bytes, of the
value in the file that is to be compared against the <i>value</i> field of the line. If the file is shorter than the specified
offset, the test shall fail.
<p>If the <i>offset</i> begins with the character <tt>'&gt;'</tt> , the test contained in the line shall not be applied to the file
unless the test on the last line for which the <i>offset</i> did not begin with a <tt>'&gt;'</tt> was successful. By default, the
<i>offset</i> shall be interpreted as an unsigned decimal number. With a leading 0x or 0X, the <i>offset</i> shall be interpreted
as a hexadecimal number; otherwise, with a leading 0, the <i>offset</i> shall be interpreted as an octal number.</p>
</dd>
<dt><i>type</i></dt>
<dd>The type of the value in the file to be tested. The type shall consist of the type specification characters <tt>c</tt> ,
<tt>d</tt> , <tt>f</tt> , <tt>s</tt> , and <tt>u</tt> , specifying character, signed decimal, floating point, string, and unsigned
decimal, respectively.
<p>The <i>type</i> string shall be interpreted as the bytes from the file starting at the specified <i>offset</i> and including the
same number of bytes specified by the <i>value</i> field. If insufficient bytes remain in the file past the <i>offset</i> to match
the <i>value</i> field, the test shall fail.</p>
<p>The type specification characters <tt>d</tt> , <tt>f</tt> , and <tt>u</tt> can be followed by an optional unsigned decimal
integer that specifies the number of bytes represented by the type. The type specification character <tt>f</tt> can be followed by
an optional <tt>F</tt> , <tt>D</tt> , or <tt>L</tt> , indicating that the value is of type <b>float</b>, <b>double</b>, or <b>long
double</b>, respectively. The type specification characters <tt>d</tt> and <tt>u</tt> can be followed by an optional <tt>C</tt> ,
<tt>S</tt> , <tt>I</tt> , or <tt>L</tt> , indicating that the value is of type <b>char</b>, <b>short</b>, <b>int</b>, or
<b>long</b>, respectively.</p>
<p>The default number of bytes represented by the type specifiers <tt>d</tt> , <tt>f</tt> , and <tt>u</tt> shall correspond to
their respective C-language types as follows. If the system claims conformance to the C-Language Development Utilities option,
those specifiers shall correspond to the default sizes used in the <a href="../utilities/c99.html"><i>c99</i></a> utility.
Otherwise, the default sizes shall be implementation-defined.</p>
<p>For the type specifier characters <tt>d</tt> and <tt>u</tt> , the default number of bytes shall correspond to the size of a
basic integer type of the implementation. For these specifier characters, the implementation shall support values of the optional
number of bytes to be converted corresponding to the number of bytes in the C-language types <b>char</b>, <b>short</b>, <b>int</b>,
or <b>long</b>. These numbers can also be specified by an application as the characters <tt>C</tt> , <tt>S</tt> , <tt>I</tt> , and
<tt>L</tt> , respectively. The byte order used when interpreting numeric values is implementation-defined, but shall correspond to
the order in which a constant of the corresponding type is stored in memory on the system.</p>
<p>For the type specifier <tt>f</tt> , the default number of bytes shall correspond to the number of bytes in the basic double
precision floating-point data type of the underlying implementation. The implementation shall support values of the optional number
of bytes to be converted corresponding to the number of bytes in the C-language types <b>float</b>, <b>double</b>, and <b>long
double</b>. These numbers can also be specified by an application as the characters <tt>F</tt> , <tt>D</tt> , and <tt>L</tt> ,
respectively.</p>
<p>All type specifiers, except for <tt>s</tt> , can be followed by a mask specifier of the form &amp;<i>number</i>. The mask value
shall be AND'ed with the value of the input file before the comparison with the <i>value</i> field of the line is made. By default,
the mask shall be interpreted as an unsigned decimal number. With a leading 0x or 0X, the mask shall be interpreted as an unsigned
hexadecimal number; otherwise, with a leading 0, the mask shall be interpreted as an unsigned octal number.</p>
<p>The strings <b>byte</b>, <b>short</b>, <b>long</b>, and <b>string</b> shall also be supported as type fields, being interpreted
as <tt>dC</tt> , <tt>dS</tt> , <tt>dL</tt> , and <tt>s</tt> , respectively.</p>
</dd>
<dt><i>value</i></dt>
<dd>The <i>value</i> to be compared with the value from the file.
<p>If the specifier from the type field is <tt>s</tt> or <b>string</b>, then interpret the value as a string. Otherwise, interpret
it as a number. If the value is a string, then the test shall succeed only when a string value exactly matches the bytes from the
file.</p>
<p>If the <i>value</i> is a string, it can contain the following sequences:</p>
<dl compact>
<dt>\<i>character</i></dt>
<dd>The backslash-escape sequences as specified in the Base Definitions volume of IEEE&nbsp;Std&nbsp;1003.1-2001, Table 5-1, Escape
Sequences and Associated Actions ( <tt>'\\'</tt> , <tt>'\a'</tt> , <tt>'\b'</tt> , <tt>'\f'</tt> , <tt>'\n'</tt> , <tt>'\r'</tt> ,
<tt>'\t'</tt> , <tt>'\v'</tt> ). The results of using any other character, other than an octal digit, following the backslash are
unspecified.</dd>
<dt>\<i>octal</i></dt>
<dd>Octal sequences that can be used to represent characters with specific coded values. An octal sequence shall consist of a
backslash followed by the longest sequence of one, two, or three octal-digit characters (01234567). If the size of a byte on the
system is greater than 9 bits, the valid escape sequence used to represent a byte is implementation-defined.</dd>
</dl>
<p>By default, any value that is not a string shall be interpreted as a signed decimal number. Any such value, with a leading 0x or
0X, shall be interpreted as an unsigned hexadecimal number; otherwise, with a leading zero, the value shall be interpreted as an
unsigned octal number.</p>
<p>If the value is not a string, it can be preceded by a character indicating the comparison to be performed. Permissible
characters and the comparisons they specify are as follows:</p>
<dl compact>
<dt><tt>=</tt></dt>
<dd>The test shall succeed if the value from the file equals the <i>value</i> field.</dd>
<dt><tt>&lt;</tt></dt>
<dd>The test shall succeed if the value from the file is less than the <i>value</i> field.</dd>
<dt><tt>&gt;</tt></dt>
<dd>The test shall succeed if the value from the file is greater than the <i>value</i> field.</dd>
<dt><tt>&amp;</tt></dt>
<dd>The test shall succeed if all of the set bits in the <i>value</i> field are set in the value from the file.</dd>
<dt><tt>^</tt></dt>
<dd>The test shall succeed if at least one of the set bits in the <i>value</i> field is not set in the value from the file.</dd>
<dt><tt>x</tt></dt>
<dd>The test shall succeed if the file is large enough to contain a value of the type specified starting at the offset
specified.</dd>
</dl>
</dd>
<dt><i>message</i></dt>
<dd>The <i>message</i> to be printed if the test succeeds. The <i>message</i> shall be interpreted using the notation for the <a
href="../utilities/printf.html"><i>printf</i></a> formatting specification; see <a href="printf.html"><i>printf</i>()</a> . If the
<i>value</i> field was a string, then the value from the file shall be the argument for the <a href=
"../utilities/printf.html"><i>printf</i></a> formatting specification; otherwise, the value from the file shall be the
argument.</dd>
</dl>
</blockquote>
<h4><a name="tag_04_54_14"></a>EXIT STATUS</h4>
<blockquote>
<p>The following exit values shall be returned:</p>
<dl compact>
<dt>&nbsp;0</dt>
<dd>Successful completion.</dd>
<dt>&gt;0</dt>
<dd>An error occurred.</dd>
</dl>
</blockquote>
<h4><a name="tag_04_54_15"></a>CONSEQUENCES OF ERRORS</h4>
<blockquote>
<p>Default.</p>
</blockquote>
<hr>
<div class="box"><em>The following sections are informative.</em></div>
<h4><a name="tag_04_54_16"></a>APPLICATION USAGE</h4>
<blockquote>
<p>The <i>file</i> utility can only be required to guess at many of the file types because only exhaustive testing can determine
some types with certainty. For example, binary data on some implementations might match the initial segment of an executable or a
<i>tar</i> archive.</p>
<p>Note that the table indicates that the output contains the stated string. Systems may add text before or after the string. For
executables, as an example, the machine architecture and various facts about how the file was link-edited may be included.</p>
</blockquote>
<h4><a name="tag_04_54_17"></a>EXAMPLES</h4>
<blockquote>
<p>Determine whether an argument is a binary executable file:</p>
<pre>
<tt>file "$1" | grep -Fq executable &amp;&amp;
printf "%s is executable.\n" "$1"
</tt>
</pre>
</blockquote>
<h4><a name="tag_04_54_18"></a>RATIONALE</h4>
<blockquote>
<p>The <b>-f</b> option was omitted because the same effect can (and should) be obtained using the <a href=
"../utilities/xargs.html"><i>xargs</i></a> utility.</p>
<p>Historical versions of the <i>file</i> utility attempt to identify the following types of files: symbolic link, directory,
character special, block special, socket, <i>tar</i> archive, <i>cpio</i> archive, SCCS archive, archive library, empty, <a href=
"../utilities/compress.html"><i>compress</i></a> output, <i>pack</i> output, binary data, C source, FORTRAN source, assembler
source, <i>nroff</i>/ <i>troff</i>/ <i>eqn</i>/ <i>tbl</i> source <i>troff</i> output, shell script, C shell script, English text,
ASCII text, various executables, APL workspace, compiled terminfo entries, and CURSES screen images. Only those types that are
reasonably well specified in POSIX or are directly related to POSIX utilities are listed in the table.</p>
<p>Historical systems have used a &quot;magic file&quot; named <b>/etc/magic</b> to help identify file types. Because it is generally
useful for users and scripts to be able to identify special file types, the <b>-m</b> flag and a portable format for user-created
magic files has been specified. No requirement is made that an implementation of <i>file</i> use this method of identifying files,
only that users be permitted to add their own classifying tests.</p>
<p>In addition, three options have been added to historical practice. The <b>-d</b> flag has been added to permit users to cause
their tests to follow any default system tests. The <b>-i</b> flag has been added to permit users to test portably for regular
files in shell scripts. The <b>-M</b> flag has been added to permit users to ignore any default system tests.</p>
<p>The historical <b>-c</b> option was omitted as not particularly useful to users or portable shell scripts. In addition, a
reasonable implementation of the <i>file</i> utility would report any errors found each time the magic file is read.</p>
<p>The historical format of the magic file was the same as that specified by the Rationale in the ISO&nbsp;POSIX-2:1993 standard
for the <i>offset</i>, <i>value</i>, and <i>message</i> fields; however, it used less precise type fields than the format specified
by the current normative text. The new type field values are a superset of the historical ones.</p>
<p>The following is an example magic file:</p>
<pre>
<tt>0 short 070707 cpio archive
0 short 0143561 Byte-swapped cpio archive
0 string 070707 ASCII cpio archive
0 long 0177555 Very old archive
0 short 0177545 Old archive
0 short 017437 Old packed data
0 string \037\036 Packed data
0 string \377\037 Compacted data
0 string \037\235 Compressed data
&gt;2 byte&amp;0x80 &gt;0 Block compressed
&gt;2 byte&amp;0x1f x %d bits
0 string \032\001 Compiled Terminfo Entry
0 short 0433 Curses screen image
0 short 0434 Curses screen image
0 string &lt;ar&gt; System V Release 1 archive
0 string !&lt;arch&gt;\n__.SYMDEF Archive random library
0 string !&lt;arch&gt; Archive
0 string ARF_BEGARF PHIGS clear text archive
0 long 0x137A2950 Scalable OpenFont binary
0 long 0x137A2951 Encrypted scalable OpenFont binary
</tt>
</pre>
<p>The use of a basic integer data type is intended to allow the implementation to choose a word size commonly used by applications
on that architecture.</p>
</blockquote>
<h4><a name="tag_04_54_19"></a>FUTURE DIRECTIONS</h4>
<blockquote>
<p>None.</p>
</blockquote>
<h4><a name="tag_04_54_20"></a>SEE ALSO</h4>
<blockquote>
<p><a href="ar.html"><i>ar</i></a> , <a href="ls.html"><i>ls</i></a> , <a href="pax.html"><i>pax</i></a></p>
</blockquote>
<h4><a name="tag_04_54_21"></a>CHANGE HISTORY</h4>
<blockquote>
<p>First released in Issue 4.</p>
</blockquote>
<h4><a name="tag_04_54_22"></a>Issue 6</h4>
<blockquote>
<p>This utility is marked as part of the User Portability Utilities option.</p>
<p>Options and an EXTENDED DESCRIPTION are added as specified in the IEEE&nbsp;P1003.2b draft standard.</p>
<p>IEEE PASC Interpretations 1003.2 #192 and #178 are applied.</p>
</blockquote>
<div class="box"><em>End of informative text.</em></div>
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