ls: seznam obsah adresáře

Originální popis anglicky: ls - list directory contents

Návod, kniha: POSIX Programmer's Manual

STRUČNĚ

ls [-CFRacdilqrtu1][-H | -L ][-fgmnopsx ][file...]

POPIS / INSTRUKCE

For each operand that names a file of a type other than directory or symbolic link to a directory, ls shall write the name of the file as well as any requested, associated information. For each operand that names a file of type directory, ls shall write the names of files contained within the directory as well as any requested, associated information. If one of the -d, -F, or -l options are specified, and one of the -H or -L options are not specified, for each operand that names a file of type symbolic link to a directory, ls shall write the name of the file as well as any requested, associated information. If none of the -d, -F, or -l options are specified, or the -H or -L options are specified, for each operand that names a file of type symbolic link to a directory, ls shall write the names of files contained within the directory as well as any requested, associated information. If no operands are specified, ls shall write the contents of the current directory. If more than one operand is specified, ls shall write non-directory operands first; it shall sort directory and non-directory operands separately according to the collating sequence in the current locale. The ls utility shall detect infinite loops; that is, entering a previously visited directory that is an ancestor of the last file encountered. When it detects an infinite loop, ls shall write a diagnostic message to standard error and shall either recover its position in the hierarchy or terminate.

OPTIONS

The ls utility shall conform to the Base Definitions volume of IEEE Std 1003.1-2001, Section 12.2, Utility Syntax Guidelines. The following options shall be supported:

-C

Write multi-text-column output with entries sorted down the columns, according to the collating sequence. The number of text columns and the column separator characters are unspecified, but should be adapted to the nature of the output device.

-F

Do not follow symbolic links named as operands unless the -H or -L options are specified. Write a slash ( '/' ) immediately after each pathname that is a directory, an asterisk ( '*' ) after each that is executable, a vertical bar ( '|' ) after each that is a FIFO, and an at sign ( '@' ) after each that is a symbolic link. For other file types, other symbols may be written.

-H

If a symbolic link referencing a file of type directory is specified on the command line, ls shall evaluate the file information and file type to be those of the file referenced by the link, and not the link itself; however, ls shall write the name of the link itself and not the file referenced by the link.

-L

Evaluate the file information and file type for all symbolic links (whether named on the command line or encountered in a file hierarchy) to be those of the file referenced by the link, and not the link itself; however, ls shall write the name of the link itself and not the file referenced by the link. When -L is used with -l, write the contents of symbolic links in the long format (see the STDOUT section).

-R

Recursively list subdirectories encountered.

-a

Write out all directory entries, including those whose names begin with a period ( '.' ). Entries beginning with a period shall not be written out unless explicitly referenced, the -a option is supplied, or an implementation-defined condition shall cause them to be written.

-c

Use time of last modification of the file status information (see <sys/stat.h> in the System Interfaces volume of IEEE Std 1003.1-2001) instead of last modification of the file itself for sorting ( -t) or writing ( -l).

-d

Do not follow symbolic links named as operands unless the -H or -L options are specified. Do not treat directories differently than other types of files. The use of -d with -R produces unspecified results.

-f

Force each argument to be interpreted as a directory and list the name found in each slot. This option shall turn off -l, -t, -s, and -r, and shall turn on -a; the order is the order in which entries appear in the directory.

-g

The same as -l, except that the owner shall not be written.

-i

For each file, write the file's file serial number (see stat() in the System Interfaces volume of IEEE Std 1003.1-2001).

-l

(The letter ell.) Do not follow symbolic links named as operands unless the -H or -L options are specified. Write out in long format (see the STDOUT section). When -l (ell) is specified, -1 (one) shall be assumed.

-m

Stream output format; list files across the page, separated by commas.

-n

The same as -l, except that the owner's UID and GID numbers shall be written, rather than the associated character strings.

-o

The same as -l, except that the group shall not be written.

-p

Write a slash ( '/' ) after each filename if that file is a directory.

-q

Force each instance of non-printable filename characters and <tab>s to be written as the question-mark ( '?' ) character. Implementations may provide this option by default if the output is to a terminal device.

-r

Reverse the order of the sort to get reverse collating sequence or oldest first.

-s

Indicate the total number of file system blocks consumed by each file displayed. The block size is implementation-defined.

-t

Sort with the primary key being time modified (most recently modified first) and the secondary key being filename in the collating sequence.

-u

Use time of last access (see <sys/stat.h>) instead of last modification of the file for sorting ( -t) or writing ( -l).

-x

The same as -C, except that the multi-text-column output is produced with entries sorted across, rather than down, the columns.

-1

(The numeric digit one.) Force output to be one entry per line.

 

Specifying more than one of the options in the following mutually-exclusive pairs shall not be considered an error: -C and -l (ell), -m and -l (ell), -x and -l (ell), -C and -1 (one), -H and -L, -c and -u. The last option specified in each pair shall determine the output format.

OPERANDS

The following operand shall be supported:

file

A pathname of a file to be written. If the file specified is not found, a diagnostic message shall be output on standard error.

 

STDIN

Not used.

INPUT FILES

None.

ENVIRONMENT VARIABLES

The following environment variables shall affect the execution of ls:

COLUMNS

Determine the user's preferred column position width for writing multiple text-column output. If this variable contains a string representing a decimal integer, the ls utility shall calculate how many pathname text columns to write (see -C) based on the width provided. If COLUMNS is not set or invalid, an implementation-defined number of column positions shall be assumed, based on the implementation's knowledge of the output device. The column width chosen to write the names of files in any given directory shall be constant. Filenames shall not be truncated to fit into the multiple text-column output.

LANG

Provide a default value for the internationalization variables that are unset or null. (See the Base Definitions volume of IEEE Std 1003.1-2001, Section 8.2, Internationalization Variables for the precedence of internationalization variables used to determine the values of locale categories.)

LC_ALL

If set to a non-empty string value, override the values of all the other internationalization variables.

LC_COLLATE

 

Determine the locale for character collation information in determining the pathname collation sequence.

LC_CTYPE

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 which characters are defined as printable (character class print).

LC_MESSAGES

Determine the locale that should be used to affect the format and contents of diagnostic messages written to standard error.

LC_TIME

Determine the format and contents for date and time strings written by ls.

NLSPATH

Determine the location of message catalogs for the processing of LC_MESSAGES .

TZ

Determine the timezone for date and time strings written by ls. If TZ is unset or null, an unspecified default timezone shall be used.

 

ASYNCHRONOUS EVENTS

Default.

STDOUT

The default format shall be to list one entry per line to standard output; the exceptions are to terminals or when one of the -C, -m, or -x options is specified. If the output is to a terminal, the format is implementation-defined. When -m is specified, the format used shall be: where the largest number of filenames shall be written without exceeding the length of the line. If the -i option is specified, the file's file serial number (see <sys/stat.h>) shall be written in the following format before any other output for the corresponding entry: If the -l option is specified without -L, the following information shall be written: If the file is a symbolic link, this information shall be about the link itself and the < pathname> field shall be of the form: If both -l and -L are specified, the following information shall be written: where all fields except < pathname of link> shall be for the file resolved from the symbolic link. The -g, -n, and -o options use the same format as -l, but with omitted items and their associated <blank>s. See the OPTIONS section. In both the preceding -l forms, if <owner name> or <group name> cannot be determined,  or if -n is given, they shall be replaced with their associated numeric values using the format %u . The < date and time> field shall contain the appropriate date and timestamp of when the file was last modified. In the POSIX locale, the field shall be the equivalent of the output of the following date command: if the file has been modified in the last six months, or: (where two <space>s are used between %e and %Y ) 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> produced by date shall not be included and the output shall be as if the date 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. If the file is a character special or block special file, the size of the file may be replaced with implementation-defined information associated with the device in question. If the pathname was specified as a file operand, it shall be written as specified. The file mode written under the -l, -g, -n, and -o options shall consist of the following format: The < optional alternate access method flag> shall be a single <space> if there is no alternate or additional access control method associated with the file; otherwise, a printable character shall be used. The < entry type> character shall describe the type of file, as follows:

d

Directory.

b

Block special file.

c

Character special file.

l (ell)

Symbolic link.

p

FIFO.

-

Regular file.

 

Implementations may add other characters to this list to represent other implementation-defined file types. The next three fields shall be three characters each:

<owner permissions>

 

Permissions for the file owner class (see the Base Definitions volume of IEEE Std 1003.1-2001, Section 4.4, File Access Permissions).

<group permissions>

 

Permissions for the file group class.

<other permissions>

 

Permissions for the file other class.

 

Each field shall have three character positions:

1.

If 'r' , the file is readable; if '-' , the file is not readable.

2.

If 'w' , the file is writable; if '-' , the file is not writable.

3.

The first of the following that applies:

S

s

T

t

x

-

Implementations may add other characters to this list for the third character position. Such additions shall, however, be written in lowercase if the file is executable or searchable, and in uppercase if it is not. If any of the -l, -g, -n, -o, or -s options is specified, each list of files within the directory shall 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 shall be: 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 -R option, each list of files within a directory shall be preceded by: If this string is the first thing to be written, the first <newline> shall not be written. This output shall precede the number of units in the directory. If the -s option is given, each file shall be written with the number of blocks used by the file. Along with -C, -1, -m, or -x, the number and a <space> shall precede the filename; with -g, -l, -n, or -o, they shall precede each line describing a file.

STDERR

The standard error shall be used only for diagnostic messages.

OUTPUT FILES

None.

EXTENDED DESCRIPTION

None.

EXIT STATUS

The following exit values shall be returned:

 0

Successful completion.

>0

An error occurred.

 

CONSEQUENCES OF ERRORS

Default. The following sections are informative.

APPLICATION USAGE

Many implementations use the equal sign ( '=' ) to denote sockets bound to the file system for the -F option. Similarly, many historical implementations use the 's' character to denote sockets as the entry type characters for the -l option. It is difficult for an application to use every part of the file modes field of ls -l 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 test utility. The output of ls (with the -l and related options) contains information that logically could be used by utilities such as chmod and touch 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 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. As with many of the utilities that deal with filenames, the output of ls 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. 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).

PŘÍKLADY POUŽITÍ

An example of a small directory tree being fully listed with ls -laRF a in the POSIX locale:

RATIONALE

Some historical implementations of the ls utility show all entries in a directory except dot and dot-dot when a superuser invokes ls without specifying the -a option. When "normal" users invoke ls without specifying -a, they should not see information about any files with names beginning with a period unless they were named as file operands. Implementations are expected to traverse arbitrary depths when processing the -R option. The only limitation on depth should be based on running out of physical storage for keeping track of untraversed directories. The -1 (one) option was historically found in BSD and BSD-derived implementations only. It is required in this volume of IEEE Std 1003.1-2001 so that conforming applications might ensure that output is one entry per line, even if the output is to a terminal. Generally, this volume of IEEE Std 1003.1-2001 is silent about what happens when options are given multiple times. In the cases of -C, -l, and -1, however, it does specify the results of these overlapping options. Since ls is one of the most aliased commands, it is important that the implementation perform intuitively. For example, if the alias were: and the user typed ls -1, single-text-column output should result, not an error. The BSD ls provides a -A option (like -a, but dot and dot-dot are not written out). The small difference from -a did not seem important enough to require both. Implementations may make -q the default for terminals to prevent trojan horse attacks on terminals with special escape sequences. This is not required because:

*

Some control characters may be useful on some terminals; for example, a system might write them as "\001" or "^A" .

*

Special behavior for terminals is not relevant to applications portability.

An early proposal specified that the optional alternate access method flag had to be '+' if there was an alternate access method used on the file or <space> if there was not. This was changed to be <space> if there is not and a single printable character if there is. This was done for three reasons:

1.

There are historical implementations using characters other than '+' .

2.

There are implementations that vary this character used in that position to distinguish between various alternate access methods in use.

3.

The standard developers did not want to preclude future specifications that might need a way to specify more than one alternate access method.

Nonetheless, implementations providing a single alternate access method are encouraged to use '+' . In an early proposal, the units used to specify the number of blocks occupied by files in a directory in an ls -l listing were implementation-defined. This was because BSD systems have historically used 1024-byte units and System V systems have historically used 512-byte units. It was pointed out by BSD developers that their system has used 512-byte units in some places and 1024-byte units in other places. (System V has consistently used 512.) Therefore, this volume of IEEE Std 1003.1-2001 usually specifies 512. Future releases of BSD are expected to consistently provide 512 bytes as a default with a way of specifying 1024-byte units where appropriate. The < date and time> field in the -l format is specified only for the POSIX locale. As noted, the format can be different in other locales. No mechanism for defining this is present in this volume of IEEE Std 1003.1-2001, as the appropriate vehicle is a messaging system; that is, the format should be specified as a "message".

FUTURE DIRECTIONS

The -s uses implementation-defined units and cannot be used portably; it may be withdrawn in a future version.

SOUVISEJÍCÍ

chmod() , find , the System Interfaces volume of IEEE Std 1003.1-2001, stat(), the Base Definitions volume of IEEE Std 1003.1-2001, <sys/stat.h>

COPYRIGHT

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .