ls.html

unix 下的C开发手册,还用详细的例程。

or if
<b>-n</b>
is given,
they are replaced
with their associated numeric values using the format
%u.
<p>
The
&lt;<i>date and time</i>&gt;,
field will contain the appropriate
date and timestamp of when the file was last modified.
In the POSIX locale, the field is the equivalent
of the output of the following
<i><a href="date.html">date</a></i>
command:
<pre>
<code>
date "+%b %e %H:%M"
</code>
</pre>
if the file has been modified in the last six months, or:
<pre>
<code>
date "+%b %e  %Y"
</code>
</pre>
(where two
space
characters are used between
<b>%e</b>
and
<b>%Y)</b>
if the file has not been modified in the last six months or if the
modification date is in the future, except that, in both cases,
the final
newline character
produced by
<i><a href="date.html">date</a></i>
is not included and
the output is as if the
<i><a href="date.html">date</a></i>
command were executed at the
time of the last modification date of the file rather than the
current time.
When the LC_TIME locale category is not set to
the POSIX locale, a different format and order of presentation
of this field may be used.
<p>
If the file is a character special or block special file, the size of the
file may be replaced with implementation-dependent information associated
with the device in question.
<p>
If the pathname was specified as a
<i>file</i>
operand, it will be written
as specified.
<p>
The file mode written under the
<b>-l</b>,
<b>-g</b>,
<b>-n</b>
and
<b>-o</b>
options consists of the following format:
<p><code>
<tt>"%c%s%s%s%c"</tt>, &lt;<i>entry&nbsp;type</i>&gt;,
&lt;<i>owner&nbsp;permissions</i>&gt;,
&lt;<i>group&nbsp;permissions</i>&gt;,
&lt;<i>other&nbsp;permissions</i>&gt;,
&lt;<i>optional&nbsp;alternate&nbsp;access&nbsp;method&nbsp;flag</i>&gt;
</code>
<p>
The
&lt;<i>optional alternate access method flag</i>&gt;
is a single
space character
if there is no alternate or additional
access control method associated with the file;
otherwise, a printable character is used.
<p>
The
&lt;<i>entry type</i>&gt;
character describes the type of file, as follows:
<dl compact>

<dt>d<dd>Directory.

<dt>b<dd>Block special file.

<dt>c<dd>Character special file.

<dt>p<dd>FIFO.

<dt>-<dd>Regular file.

</dl>
<p>
Implementations may add other characters to this list to represent
other, implementation-dependent, file types.
<p>
The next three fields are three characters each:
<dl compact>

<dt>&lt;<i>owner permissions</i>&gt;<dd>
Permissions for the file owner class (see
<b>file access permissions</b>
in
the <b>XBD</b> specification, <a href="../xbd/glossary.html"><b>Glossary</b>&nbsp;</a> ).

<dt>&lt;<i>group permissions</i>&gt;<dd>
Permissions for the file group class.

<dt>&lt;<i>other permissions</i>&gt;<dd>
Permissions for the file other class.

</dl>
<p>
Each field has three character positions:
<p>
<ol>
<li>
If
r,
the file is readable; if "-", it is not readable.
<p>
<li>
If
w,
the file is writable; if "-", it is not writable.
<p>
<li>
The first of the following that applies:
<dl compact>

<dt><b>S</b><dd>If in
&lt;<i>owner permissions</i>&gt;,
the file is not executable and
set-user-ID mode is set.
If in
&lt;<i>group permissions</i>&gt;,
the file is not executable and set-group-ID mode is set.

<dt><b>s</b><dd>If in
&lt;<i>owner permissions</i>&gt;,
the file is executable and
set-user-ID mode is set.
If in
&lt;<i>group permissions</i>&gt;,
the file is executable and set-group-ID mode is set.

<dt><b>x</b><dd>The file is executable or the directory is searchable.

<dt><b>-</b><dd>None of the attributes of
S,
s
or
x
applies.

</dl>
<p>
Implementations may add other characters to this list for the third
character position.
Such additions will, however, be written in
lower-case if the file is executable or searchable, and in upper-case
if it is not.
<p>
</ol>
<p>
If any of the
<b>-l</b>,
<b>-g</b>,
<b>-n</b>,
<b>-o</b>
or
<b>-s</b>
options is specified,
each list of files within the directory will be
preceded by a status line indicating the number of file system
blocks occupied by files in the directory in
512-byte units, rounded up to the next integral
number of units, if necessary.
In the POSIX locale, the format is:
<p><code>
<tt>"total %u\n"</tt>, &lt;<i>number of units in the directory</i>&gt;
</code>
<p>
If more than one directory, or a combination of non-directory files and
directories are written, either as a result of specifying multiple
operands, or the
<b>-R</b>
option, each list of files within a directory will be preceded by:
<p><code>
<tt>"\n%s:\n"</tt>, &lt;<i>directory name</i>&gt;
</code>
<p>
If this string is the first thing to be written, the first
newline
character is not written.
This output precedes the number of units in the directory.
<p>
If the
<b>-s</b>
option is given, each file shall be written
with the number of blocks used by the file.
Along with
<b>-C</b>,
<b>-1</b>,
<b>-m</b>
or
<b>-x</b>,
the number and a
space character
precede the filename; with
<b>-g</b>,
<b>-l</b>,
<b>-n</b>
or
<b>-o</b>,
they precede each line describing a file.
</blockquote><h4><a name = "tag_001_014_1299">&nbsp;</a>STDERR</h4><blockquote>
Used only for diagnostic messages.
</blockquote><h4><a name = "tag_001_014_1300">&nbsp;</a>OUTPUT FILES</h4><blockquote>
None.
</blockquote><h4><a name = "tag_001_014_1301">&nbsp;</a>EXTENDED DESCRIPTION</h4><blockquote>
None.
</blockquote><h4><a name = "tag_001_014_1302">&nbsp;</a>EXIT STATUS</h4><blockquote>
The following exit values are returned:
<dl compact>

<dt>0<dd>All files were written successfully.

<dt>&gt;0<dd>An error occurred.

</dl>
</blockquote><h4><a name = "tag_001_014_1303">&nbsp;</a>CONSEQUENCES OF ERRORS</h4><blockquote>
Default.
</blockquote><h4><a name = "tag_001_014_1304">&nbsp;</a>APPLICATION USAGE</h4><blockquote>
Many implementations use the equal sign
(=)
and the at sign
(@)
to denote
sockets bound to the file system and symbolic links, respectively, for the
<b>-F</b>
option.
Similarly, many historical implementations use the
s
character and the
l
character to denote sockets and symbolic links,
respectively, as the entry type characters for the
<b>-l</b>
option.
<p>
It is difficult for an application to use every part of the file modes
field of
<i>ls</i>
<b>-l</b>
in a portable manner.
Certain file types and executable
bits are not guaranteed to be exactly as shown, as implementations may
have extensions.
Applications can use this field to pass directly to
a user printout or prompt, but actions based on its contents should
generally be deferred, instead, to the
<i><a href="test.html">test</a></i>
utility.
<p>
The output of
<i>ls</i>
(with the
<b>-l</b>
and related options) contains information that
logically could be used by utilities such as
<i><a href="chmod.html">chmod</a></i>
and
<i><a href="touch.html">touch</a></i>
to restore files to a known state.
However, this information is presented in a format
that cannot be used directly by those utilities or be easily
translated into a format that can be used.
A character has been added to the end of the permissions
string so that applications will at least have an indication
that they may be working in an area they do not understand
instead of assuming that they can translate the permissions
string into something that can be used.
Future issues or related documents may define one
or more specific characters to be used based on different
standard additional or alternative access control mechanisms.
<p>
As with many of the utilities that deal with filenames,
the output of
<i>ls</i>
for multiple files or in one of the long listing formats
must be used carefully on systems where filenames can
contain embedded white space.
Systems and system administrators
should institute policies and user training to limit the
use of such filenames.
<p>
The number of disk blocks occupied
by the file that it reports varies depending on underlying file
system type, block size units reported and the method of
calculating the number of blocks.
On some file system types,
the number is the actual number of blocks occupied by the file
(counting indirect blocks and ignoring holes in the file); on
others it is calculated based on the file size (usually making
an allowance for indirect blocks, but ignoring holes).
</blockquote><h4><a name = "tag_001_014_1305">&nbsp;</a>EXAMPLES</h4><blockquote>
An example of a small directory tree being fully listed with
<i>ls</i>
<b>-laRF</b>
<b>a</b>
in the POSIX locale:
<pre>
<code>
total 11
drwxr-xr-x   3 hlj      prog          64 Jul  4 12:07 ./
drwxrwxrwx   4 hlj      prog        3264 Jul  4 12:09 ../
drwxr-xr-x   2 hlj      prog          48 Jul  4 12:07 b/
-rwxr--r--   1 hlj      prog         572 Jul  4 12:07 foo*

a/b:
total 4
drwxr-xr-x   2 hlj      prog          48 Jul  4 12:07 ./
drwxr-xr-x   3 hlj      prog          64 Jul  4 12:07 ../
-rw-r--r--   1 hlj      prog         700 Jul  4 12:07 bar
</code>
</pre>
</blockquote><h4><a name = "tag_001_014_1306">&nbsp;</a>FUTURE DIRECTIONS</h4><blockquote>
The
<b>-s</b>
uses implementation-dependent units and cannot be used portably;
it may be withdrawn in a future issue.
<p>
The IEEE PASC 1003.2 Interpretations Committee has forwarded concerns about
parts of this interface definition to the IEEE PASC Shell and Utilities Working Group
which is identifying the corrections.
A future revision of this specification will align with
IEEE Std. 1003.2b when finalised.
</blockquote><h4><a name = "tag_001_014_1307">&nbsp;</a>SEE ALSO</h4><blockquote>
<i><a href="chmod.html">chmod</a></i>,
<i><a href="find.html">find</a></i>,
the <b>XSH</b> specification description of
<i><a href="../xsh/sysstat.h.html">&lt;sys/stat.h&gt;</a></i>.
</blockquote><hr size=2 noshade>
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