GNU file utilities

This manual documents version 4.1 of the GNU file utilities.

1. Introduction		Caveats, overview, and authors.
2. Common options
3. File permissions		Access modes.
4. Date input formats		Specifying date strings.
5. Directory listing		ls dir vdir d v dircolors
6. Basic operations		cp dd install mv rm shred
7. Special file types		ln mkdir rmdir mkfifo mknod
8. Changing file attributes		chgrp chmod chown touch
9. Disk usage		df du sync
Index		General index.

1. Introduction

This manual is incomplete: No attempt is made to explain basic file concepts in a way suitable for novices. Thus, if you are interested, please get involved in improving this manual. The entire GNU community will benefit.

The GNU file utilities are mostly compatible with the POSIX.2 standard.

Please report bugs to bug-fileutils@gnu.org. Remember to include the version number, machine architecture, input files, and any other information needed to reproduce the bug: your input, what you expected, what you got, and why it is wrong. Diffs are welcome, but please include a description of the problem as well, since this is sometimes difficult to infer. See section `Bugs' in GNU CC.

This manual was originally derived from the Unix man pages in the distribution, which were written by David MacKenzie and updated by Jim Meyering. What you are reading now is the authoritative documentation for these utilities; the man pages are no longer being maintained. François Pinard did the initial conversion to Texinfo format. Karl Berry did the indexing, some reorganization, and editing of the results. Richard Stallman contributed his usual invaluable insights to the overall process.

2. Common options

Certain options are available in all of these programs (in fact, every GNU program should accept them). Rather than writing identical descriptions for each of the programs, they are described here.

`--help'

Print a usage message listing all available options, then exit successfully.

`--version'

Print the version number, then exit successfully.

2.1 Backup options		-b -S -V, in some programs.
2.2 Block size		BLOCK_SIZE and --block-size, in some programs.
2.3 Target directory		--target-directory, in some programs.
2.4 Trailing slashes		--strip-trailing-slashes, in some programs.

2.1 Backup options

Some GNU programs (at least cp, install, ln, and mv) optionally make backups of files before writing new versions. These options control the details of these backups. The options are also briefly mentioned in the descriptions of the particular programs.

`-b'

`--backup[=method]'

Make a backup of each file that would otherwise be overwritten or removed. Without this option, the original versions are destroyed. Use method to determine the type of backups to make. When this option is used but method is not specified, then the value of the VERSION_CONTROL environment variable is used. And if VERSION_CONTROL is not set, the default backup type is `existing'.

Note that the short form of this option, `-b' does not accept any argument. Using `-b' is equivalent to using `--backup=existing'.

This option corresponds to the Emacs variable `version-control'; the values for method are the same as those used in Emacs. This option also accepts more descriptive names. The valid methods are (unique abbreviations are accepted):

`none'

`off'

Never make backups.

`numbered'

`t'

Always make numbered backups.

`existing'

`nil'

Make numbered backups of files that already have them, simple backups of the others.

`simple'

`never'

Always make simple backups. Please note `never' is not to be confused with `none'.

`-S suffix'

`--suffix=suffix'

Append suffix to each backup file made with `-b'. If this option is not specified, the value of the SIMPLE_BACKUP_SUFFIX environment variable is used. And if SIMPLE_BACKUP_SUFFIX is not set, the default is `~', just as in Emacs.

`--version-control=method'

This option is obsolete and will be removed in a future release. It has been replaced with --backup.

2.2 Block size

Some GNU programs (at least df, du, and ls) display file sizes in "blocks". You can adjust the block size to make file sizes easier to read. The block size used for display is independent of any filesystem block size.

Normally, disk usage sizes are rounded up, disk free space sizes are rounded down, and other sizes are rounded to the nearest value with ties rounding to an even value.

The default block size is chosen by examining the following environment variables in turn; the first one that is set determines the block size.

DF_BLOCK_SIZE

This specifies the default block size for the df command. Similarly, DU_BLOCK_SIZE specifies the default for du and LS_BLOCK_SIZE for ls.

BLOCK_SIZE

This specifies the default block size for all three commands, if the above command-specific environment variables are not set.

POSIXLY_CORRECT

If neither the command_BLOCK_SIZE nor the BLOCK_SIZE variables are set, but this variable is set, the block size defaults to 512.

If none of the above environment variables are set, the block size currently defaults to 1024 bytes, but this number may change in the future.

A block size specification can be a positive integer specifying the number of bytes per block, or it can be human-readable or si to select a human-readable format.

With human-readable formats, output sizes are followed by a size letter such as `M' for megabytes. BLOCK_SIZE=human-readable uses powers of 1024; `M' stands for 1,048,576 bytes. BLOCK_SIZE=si is similar, but uses powers of 1000; `M' stands for 1,000,000 bytes. (SI, the International System of Units, defines these power-of-1000 prefixes.)

An integer block size can be followed by a size letter to specify a multiple of that size. When this notation is used, the size letters normally stand for powers of 1024, and can be followed by an optional `B' for "byte"; but if followed by `D' (for "decimal byte"), they stand for powers of 1000. For example, BLOCK_SIZE=4MB is equivalent to BLOCK_SIZE=4194304, and BLOCK_SIZE=4MD is equivalent to BLOCK_SIZE=4000000.

The following size letters are defined. Large sizes like 1Y may be rejected by your computer due to limitations of its arithmetic.

`k'

kilo: 2^10 = 1024 for human-readable, or 10^3 = 1000 for si.

`M'

Mega: 2^20 = 1,048,576 or 10^6 = 1,000,000.

`G'

Giga: 2^30 = 1,073,741,824 or 10^9 = 1,000,000,000.

`T'

Tera: 2^40 = 1,099,511,627,776 or 10^12 = 1,000,000,000,000.

`P'

Peta: 2^50 = 1,125,899,906,842,624 or 10^15 = 1,000,000,000,000,000.

`E'

Exa: 2^60 = 1,152,921,504,606,846,976 or 10^18 = 1,000,000,000,000,000,000.

`Z'

Zetta: 2^70 = 1,180,591,620,717,411,303,424 or 10^21 = 1,000,000,000,000,000,000,000.

`Y'

Yotta: 2^80 = 1,208,925,819,614,629,174,706,176 or 10^24 = 1,000,000,000,000,000,000,000,000.

Block size defaults can be overridden by an explicit `--block-size=size' option. The `-k' or `--kilobytes' option is equivalent to `--block-size=1k', which is the default unless the POSIXLY_CORRECT environment variable is set. The `-h' or `--human-readable' option is equivalent to `--block-size=human-readable'. The `--si' option is equivalent to `--block-size=si'.

2.3 Target directory

Some GNU programs (at least cp, install, ln, and mv) allow you to specify the target directory via this option:

`--target-directory=directory'

Specify the destination directory.

The interface for most programs is that after processing options and a finite (possibly zero) number of fixed-position arguments, the remaining argument list is either expected to be empty, or is a list of items (usually files) that will all be handled identically. The xargs program is designed to work well with this convention.

The commands in the mv-family are unusual in that they take a variable number of arguments with a special case at the end (namely, the target directory). This makes it nontrivial to perform some operations, e.g., "move all files from here to ../d/", because mv * ../d/ might exhaust the argument space, and ls | xargs ... doesn't have a clean way to specify an extra final argument for each invocation of the subject command. (It can be done by going through a shell command, but that requires more human labor and brain power than it should.)

The --target-directory option allows the cp, install, ln, and mv programs to be used conveniently with xargs. For example, you can move the files from the current directory to a sibling directory, d like this: (However, this doesn't move files whose names begin with `.'.)

ls |xargs mv --target-directory=../d

If you use the GNU find program, you can move all files with this command:

find . -mindepth 1 -maxdepth 1 \ | xargs mv --target-directory=../d

But that will fail if there are no files in the current directory or if any file has a name containing a newline character. The following example removes those limitations and requires both GNU find and GNU xargs:

find . -mindepth 1 -maxdepth 1 -print0 \ | xargs --null --no-run-if-empty \ mv --target-directory=../d

2.4 Trailing slashes

Some GNU programs (at least cp and mv) allow you to remove any trailing slashes from each source argument before operating on it. The --strip-trailing-slashes option enables this behavior.

This is useful when a source argument may have a trailing slash and specify a symbolic link to a directory. This scenario is in fact rather common because some shells can automatically append a trailing slash when performing file name completion on such symbolic links. Without this option, mv, for example, (via the system's rename function) must interpret a trailing slash as a request to dereference the symbolic link and so must rename the indirectly referenced directory and not the symbolic link. Although it may seem surprising that such behavior be the default, it is required by POSIX.2 and is consistent with other parts of that standard.

3. File permissions

Each file has a set of permissions that control the kinds of access that users have to that file. The permissions for a file are also called its access mode. They can be represented either in symbolic form or as an octal number.

3.1 Structure of File Permissions		Structure of file permissions.
3.2 Symbolic Modes		Mnemonic permissions representation.
3.3 Numeric Modes		Permissions as octal numbers.

3.1 Structure of File Permissions

There are three kinds of permissions that a user can have for a file:

1. permission to read the file. For directories, this means permission to list the contents of the directory.
2. permission to write to (change) the file. For directories, this means permission to create and remove files in the directory.
3. permission to execute the file (run it as a program). For directories, this means permission to access files in the directory.

There are three categories of users who may have different permissions to perform any of the above operations on a file:

1. the file's owner;
2. other users who are in the file's group;
3. everyone else.

Files are given an owner and group when they are created. Usually the owner is the current user and the group is the group of the directory the file is in, but this varies with the operating system, the filesystem the file is created on, and the way the file is created. You can change the owner and group of a file by using the chown and chgrp commands.

In addition to the three sets of three permissions listed above, a file's permissions have three special components, which affect only executable files (programs) and, on some systems, directories:

1. set the process's effective user ID to that of the file upon execution (called the setuid bit). No effect on directories.
2. set the process's effective group ID to that of the file upon execution (called the setgid bit). For directories on some systems, put files created in the directory into the same group as the directory, no matter what group the user who creates them is in.
3. save the program's text image on the swap device so it will load more quickly when run (called the sticky bit). For directories on some systems, prevent users from removing or renaming a file in a directory unless they own the file or the directory; this is called the restriction deletion flag for the directory.

3.2 Symbolic Modes

Symbolic modes represent changes to files' permissions as operations on single-character symbols. They allow you to modify either all or selected parts of files' permissions, optionally based on their previous values, and perhaps on the current umask as well (see section 3.2.6 The Umask and Protection).

The format of symbolic modes is:

[ugoa...][[+-=][rwxXstugo...]...][,...]

The following sections describe the operators and other details of symbolic modes.

3.2.1 Setting Permissions		Basic operations on permissions.
3.2.2 Copying Existing Permissions		Copying existing permissions.
3.2.3 Changing Special Permissions		Special permissions.
3.2.4 Conditional Executability		Conditionally affecting executability.
3.2.5 Making Multiple Changes		Making multiple changes.
3.2.6 The Umask and Protection		The effect of the umask.

3.2.1 Setting Permissions

The basic symbolic operations on a file's permissions are adding, removing, and setting the permission that certain users have to read, write, and execute the file. These operations have the following format:

users operation permissions

The spaces between the three parts above are shown for readability only; symbolic modes cannot contain spaces.

The users part tells which users' access to the file is changed. It consists of one or more of the following letters (or it can be empty; see section 3.2.6 The Umask and Protection, for a description of what happens then). When more than one of these letters is given, the order that they are in does not matter.

u

the user who owns the file;

g

other users who are in the file's group;

o

all other users;

a

all users; the same as `ugo'.

The operation part tells how to change the affected users' access to the file, and is one of the following symbols:

+

to add the permissions to whatever permissions the users already have for the file;

-

to remove the permissions from whatever permissions the users already have for the file;

=

to make the permissions the only permissions that the users have for the file.

The permissions part tells what kind of access to the file should be changed; it is zero or more of the following letters. As with the users part, the order does not matter when more than one letter is given. Omitting the permissions part is useful only with the `=' operation, where it gives the specified users no access at all to the file.

r

the permission the users have to read the file;

w

the permission the users have to write to the file;

x

the permission the users have to execute the file.

For example, to give everyone permission to read and write a file, but not to execute it, use:

a=rw

To remove write permission for from all users other than the file's owner, use:

go-w

The above command does not affect the access that the owner of the file has to it, nor does it affect whether other users can read or execute the file.

To give everyone except a file's owner no permission to do anything with that file, use the mode below. Other users could still remove the file, if they have write permission on the directory it is in.

go=

Another way to specify the same thing is:

og-rxw

3.2.2 Copying Existing Permissions

You can base a file's permissions on its existing permissions. To do this, instead of using `r', `w', or `x' after the operator, you use the letter `u', `g', or `o'. For example, the mode

o+g

adds the permissions for users who are in a file's group to the permissions that other users have for the file. Thus, if the file started out as mode 664 (`rw-rw-r--'), the above mode would change it to mode 666 (`rw-rw-rw-'). If the file had started out as mode 741 (`rwxr----x'), the above mode would change it to mode 745 (`rwxr--r-x'). The `-' and `=' operations work analogously.

3.2.3 Changing Special Permissions

In addition to changing a file's read, write, and execute permissions, you can change its special permissions. See section 3.1 Structure of File Permissions, for a summary of these permissions.

To change a file's permission to set the user ID on execution, use `u' in the users part of the symbolic mode and `s' in the permissions part.

To change a file's permission to set the group ID on execution, use `g' in the users part of the symbolic mode and `s' in the permissions part.

To change a file's permission to stay permanently on the swap device, use `o' in the users part of the symbolic mode and `t' in the permissions part.

For example, to add set user ID permission to a program, you can use the mode:

u+s

To remove both set user ID and set group ID permission from it, you can use the mode:

ug-s

To cause a program to be saved on the swap device, you can use the mode:

o+t

Remember that the special permissions only affect files that are executable, plus, on some systems, directories (on which they have different meanings; see section 3.1 Structure of File Permissions). Also, the combinations `u+t', `g+t', and `o+s' have no effect.

The `=' operator is not very useful with special permissions; for example, the mode:

o=t

does cause the file to be saved on the swap device, but it also removes all read, write, and execute permissions that users not in the file's group might have had for it.

3.2.4 Conditional Executability

There is one more special type of symbolic permission: if you use `X' instead of `x', execute permission is affected only if the file already had execute permission or is a directory. It affects directories' execute permission even if they did not initially have any execute permissions set.

For example, this mode:

a+X

gives all users permission to execute files (or search directories) if anyone could before.

3.2.5 Making Multiple Changes

The format of symbolic modes is actually more complex than described above (see section 3.2.1 Setting Permissions). It provides two ways to make multiple changes to files' permissions.

The first way is to specify multiple operation and permissions parts after a users part in the symbolic mode.

For example, the mode:

og+rX-w

gives users other than the owner of the file read permission and, if it is a directory or if someone already had execute permission to it, gives them execute permission; and it also denies them write permission to the file. It does not affect the permission that the owner of the file has for it. The above mode is equivalent to the two modes:

og+rX og-w

The second way to make multiple changes is to specify more than one simple symbolic mode, separated by commas. For example, the mode:

a+r,go-w

gives everyone permission to read the file and removes write permission on it for all users except its owner. Another example:

u=rwx,g=rx,o=

sets all of the non-special permissions for the file explicitly. (It gives users who are not in the file's group no permission at all for it.)

The two methods can be combined. The mode:

a+r,g+x-w

gives all users permission to read the file, and gives users who are in the file's group permission to execute it, as well, but not permission to write to it. The above mode could be written in several different ways; another is:

u+r,g+rx,o+r,g-w

3.2.6 The Umask and Protection

If the users part of a symbolic mode is omitted, it defaults to `a' (affect all users), except that any permissions that are set in the system variable umask are not affected. The value of umask can be set using the umask command. Its default value varies from system to system.

Omitting the users part of a symbolic mode is generally not useful with operations other than `+'. It is useful with `+' because it allows you to use umask as an easily customizable protection against giving away more permission to files than you intended to.

As an example, if umask has the value 2, which removes write permission for users who are not in the file's group, then the mode:

+w

adds permission to write to the file to its owner and to other users who are in the file's group, but not to other users. In contrast, the mode:

a+w

ignores umask, and does give write permission for the file to all users.

3.3 Numeric Modes

File permissions are stored internally as integers. As an alternative to giving a symbolic mode, you can give an octal (base 8) number that corresponds to the internal representation of the new mode. This number is always interpreted in octal; you do not have to add a leading 0, as you do in C. Mode 0055 is the same as mode 55.

A numeric mode is usually shorter than the corresponding symbolic mode, but it is limited in that it cannot take into account a file's previous permissions; it can only set them absolutely.

On most systems, the permissions granted to the user, to other users in the file's group, and to other users not in the file's group are each stored as three bits, which are represented as one octal digit. The three special permissions are also each stored as one bit, and they are as a group represented as another octal digit. Here is how the bits are arranged, starting with the lowest valued bit:

Value in Corresponding Mode Permission Other users not in the file's group: 1 Execute 2 Write 4 Read Other users in the file's group: 10 Execute 20 Write 40 Read The file's owner: 100 Execute 200 Write 400 Read Special permissions: 1000 Save text image on swap device 2000 Set group ID on execution 4000 Set user ID on execution

For example, numeric mode 4755 corresponds to symbolic mode `u=rwxs,go=rx', and numeric mode 664 corresponds to symbolic mode `ug=rw,o=r'. Numeric mode 0 corresponds to symbolic mode `ugo='.

4. Date input formats

First, a quote:

Our units of temporal measurement, from seconds on up to months, are so complicated, asymmetrical and disjunctive so as to make coherent mental reckoning in time all but impossible. Indeed, had some tyrannical god contrived to enslave our minds to time, to make it all but impossible for us to escape subjection to sodden routines and unpleasant surprises, he could hardly have done better than handing down our present system. It is like a set of trapezoidal building blocks, with no vertical or horizontal surfaces, like a language in which the simplest thought demands ornate constructions, useless particles and lengthy circumlocutions. Unlike the more successful patterns of language and science, which enable us to face experience boldly or at least level-headedly, our system of temporal calculation silently and persistently encourages our terror of time.

... It is as though architects had to measure length in feet, width in meters and height in ells; as though basic instruction manuals demanded a knowledge of five different languages. It is no wonder then that we often look into our own immediate past or future, last Tuesday or a week from Sunday, with feelings of helpless confusion. ...

--- Robert Grudin, Time and the Art of Living.

This section describes the textual date representations that GNU programs accept. These are the strings you, as a user, can supply as arguments to the various programs. The C interface (via the getdate function) is not described here.

Although the date syntax here can represent any possible time since the year zero, computer integers often cannot represent such a wide range of time. On POSIX systems, the clock starts at 1970-01-01 00:00:00 UTC: POSIX does not require support for times before the POSIX Epoch and times far in the future. Traditional Unix systems have 32-bit signed time_t and can represent times from 1901-12-13 20:45:52 through 2038-01-19 03:14:07 UTC. Systems with 64-bit signed time_t can represent all the times in the known lifetime of the universe.

4.1 General date syntax		Common rules.
4.2 Calendar date items		19 Dec 1994.
4.3 Time of day items		9:20pm.
4.4 Time zone items		EST, PDT, GMT, ...
4.5 Day of week items		Monday and others.
4.6 Relative items in date strings		next tuesday, 2 years ago.
4.7 Pure numbers in date strings		19931219, 1440.
4.8 Authors of getdate		Bellovin, Eggert, Salz, Berets, et al.

4.1 General date syntax

A date is a string, possibly empty, containing many items separated by whitespace. The whitespace may be omitted when no ambiguity arises. The empty string means the beginning of today (i.e., midnight). Order of the items is immaterial. A date string may contain many flavors of items:

• calendar date items
• time of the day items
• time zone items
• day of the week items
• relative items
• pure numbers.

We describe each of these item types in turn, below.

A few numbers may be written out in words in most contexts. This is most useful for specifying day of the week items or relative items (see below). Here is the list: `first' for 1, `next' for 2, `third' for 3, `fourth' for 4, `fifth' for 5, `sixth' for 6, `seventh' for 7, `eighth' for 8, `ninth' for 9, `tenth' for 10, `eleventh' for 11 and `twelfth' for 12. Also, `last' means exactly -1.

When a month is written this way, it is still considered to be written numerically, instead of being "spelled in full"; this changes the allowed strings.

In the current implementation, only English is supported for words and abbreviations like `AM', `DST', `EST', `first', `January', `Sunday', `tomorrow', and `year'.

The output of date is not always acceptable as a date string, not only because of the language problem, but also because there is no standard meaning for time zone items like `IST'. When using date to generate a date string intended to be parsed later, specify a date format that is independent of language and that does not use time zone items other than `UTC' and `Z'. Here are some ways to do this:

$ LC_ALL=C TZ=UTC0 date Fri Dec 15 19:48:05 UTC 2000 $ TZ=UTC0 date +"%Y-%m-%d %H:%M:%SZ" 2000-12-15 19:48:05Z $ date --iso-8601=seconds # a GNU extension 2000-12-15T11:48:05-0800 $ date --rfc-822 # a GNU extension Fri, 15 Dec 2000 11:48:05 -0800 $ date +"%Y-%m-%d %H:%M:%S %z" # %z is a GNU extension. 2000-12-15 11:48:05 -0800

Alphabetic case is completely ignored in dates. Comments may be introduced between round parentheses, as long as included parentheses are properly nested. Hyphens not followed by a digit are currently ignored. Leading zeros on numbers are ignored.

4.2 Calendar date items

A calendar date item specifies a day of the year. It is specified differently, depending on whether the month is specified numerically or literally. All these strings specify the same calendar date:

1972-09-24 # ISO 8601. 72-9-24 # Assume 19xx for 69 through 99, # 20xx for 00 through 68. 72-09-24 # Leading zeros are ignored. 9/24/72 # Common U.S. writing. 24 September 1972 24 Sept 72 # September has a special abbreviation. 24 Sep 72 # Three-letter abbreviations always allowed. Sep 24, 1972 24-sep-72 24sep72

The year can also be omitted. In this case, the last specified year is used, or the current year if none. For example:

9/24 sep 24

Here are the rules.

For numeric months, the ISO 8601 format `year-month-day' is allowed, where year is any positive number, month is a number between 01 and 12, and day is a number between 01 and 31. A leading zero must be present if a number is less than ten. If year is 68 or smaller, then 2000 is added to it; otherwise, if year is less than 100, then 1900 is added to it. The construct `month/day/year', popular in the United States, is accepted. Also `month/day', omitting the year.

Literal months may be spelled out in full: `January', `February', `March', `April', `May', `June', `July', `August', `September', `October', `November' or `December'. Literal months may be abbreviated to their first three letters, possibly followed by an abbreviating dot. It is also permitted to write `Sept' instead of `September'.

When months are written literally, the calendar date may be given as any of the following:

day month year day month month day year day-month-year

Or, omitting the year:

month day

4.3 Time of day items

A time of day item in date strings specifies the time on a given day. Here are some examples, all of which represent the same time:

20:02:0 20:02 8:02pm 20:02-0500 # In EST (U.S. Eastern Standard Time).

More generally, the time of the day may be given as `hour:minute:second', where hour is a number between 0 and 23, minute is a number between 0 and 59, and second is a number between 0 and 59. Alternatively, `:second' can be omitted, in which case it is taken to be zero.

If the time is followed by `am' or `pm' (or `a.m.' or `p.m.'), hour is restricted to run from 1 to 12, and `:minute' may be omitted (taken to be zero). `am' indicates the first half of the day, `pm' indicates the second half of the day. In this notation, 12 is the predecessor of 1: midnight is `12am' while noon is `12pm'. (This is the zero-oriented interpretation of `12am' and `12pm', as opposed to the old tradition derived from Latin which uses `12m' for noon and `12pm' for midnight.)

The time may alternatively be followed by a time zone correction, expressed as `shhmm', where s is `+' or `-', hh is a number of zone hours and mm is a number of zone minutes. When a time zone correction is given this way, it forces interpretation of the time relative to Coordinated Universal Time (UTC), overriding any previous specification for the time zone or the local time zone. The minute part of the time of the day may not be elided when a time zone correction is used. This is the best way to specify a time zone correction by fractional parts of an hour.

Either `am'/`pm' or a time zone correction may be specified, but not both.

4.4 Time zone items

A time zone item specifies an international time zone, indicated by a small set of letters, e.g., `UTC' or `Z' for Coordinated Universal Time. Any included periods are ignored. By following a non-daylight-saving time zone by the string `DST' in a separate word (that is, separated by some white space), the corresponding daylight saving time zone may be specified.

Time zone items other than `UTC' and `Z' are obsolescent and are not recommended, because they are ambiguous; for example, `EST' has a different meaning in Australia than in the United States. Instead, it's better to use unambiguous numeric time zone corrections like `-0500', as described in the previous section.

4.5 Day of week items

The explicit mention of a day of the week will forward the date (only if necessary) to reach that day of the week in the future.

Days of the week may be spelled out in full: `Sunday', `Monday', `Tuesday', `Wednesday', `Thursday', `Friday' or `Saturday'. Days may be abbreviated to their first three letters, optionally followed by a period. The special abbreviations `Tues' for `Tuesday', `Wednes' for `Wednesday' and `Thur' or `Thurs' for `Thursday' are also allowed.

A number may precede a day of the week item to move forward supplementary weeks. It is best used in expression like `third monday'. In this context, `last day' or `next day' is also acceptable; they move one week before or after the day that day by itself would represent.

A comma following a day of the week item is ignored.

4.6 Relative items in date strings

Relative items adjust a date (or the current date if none) forward or backward. The effects of relative items accumulate. Here are some examples:

1 year 1 year ago 3 years 2 days

The unit of time displacement may be selected by the string `year' or `month' for moving by whole years or months. These are fuzzy units, as years and months are not all of equal duration. More precise units are `fortnight' which is worth 14 days, `week' worth 7 days, `day' worth 24 hours, `hour' worth 60 minutes, `minute' or `min' worth 60 seconds, and `second' or `sec' worth one second. An `s' suffix on these units is accepted and ignored.

The unit of time may be preceded by a multiplier, given as an optionally signed number. Unsigned numbers are taken as positively signed. No number at all implies 1 for a multiplier. Following a relative item by the string `ago' is equivalent to preceding the unit by a multiplier with value -1.

The string `tomorrow' is worth one day in the future (equivalent to `day'), the string `yesterday' is worth one day in the past (equivalent to `day ago').

The strings `now' or `today' are relative items corresponding to zero-valued time displacement, these strings come from the fact a zero-valued time displacement represents the current time when not otherwise changed by previous items. They may be used to stress other items, like in `12:00 today'. The string `this' also has the meaning of a zero-valued time displacement, but is preferred in date strings like `this thursday'.

When a relative item causes the resulting date to cross a boundary where the clocks were adjusted, typically for daylight-saving time, the resulting date and time are adjusted accordingly.

4.7 Pure numbers in date strings

The precise interpretation of a pure decimal number depends on the context in the date string.

If the decimal number is of the form yyyymmdd and no other calendar date item (see section 4.2 Calendar date items) appears before it in the date string, then yyyy is read as the year, mm as the month number and dd as the day of the month, for the specified calendar date.

If the decimal number is of the form hhmm and no other time of day item appears before it in the date string, then hh is read as the hour of the day and mm as the minute of the hour, for the specified time of the day. mm can also be omitted.

If both a calendar date and a time of day appear to the left of a number in the date string, but no relative item, then the number overrides the year.

4.8 Authors of getdate

getdate was originally implemented by Steven M. Bellovin (smb@research.att.com) while at the University of North Carolina at Chapel Hill. The code was later tweaked by a couple of people on Usenet, then completely overhauled by Rich $alz (rsalz@bbn.com) and Jim Berets (jberets@bbn.com) in August, 1990. Various revisions for the GNU system were made by David MacKenzie, Jim Meyering, Paul Eggert and others.

This chapter was originally produced by François Pinard (pinard@iro.umontreal.ca) from the `getdate.y' source code, and then edited by K. Berry (kb@cs.umb.edu).

5. Directory listing

This chapter describes the ls command and its variants dir and vdir, which list information about files.

5.1 ls: List directory contents		List directory contents.
5.2 dir: Briefly list directory contents		Briefly ls.
5.3 vdir: Verbosely list directory contents		Verbosely ls.
5.4 dircolors: Color setup for ls		Color setup for ls, etc.

5.1 ls: List directory contents

The ls program lists information about files (of any type, including directories). Options and file arguments can be intermixed arbitrarily, as usual.

For non-option command-line arguments that are directories, by default ls lists the contents of directories, not recursively, and omitting files with names beginning with `.'. For other non-option arguments, by default ls lists just the file name. If no non-option arguments are specified, ls lists the contents of the current directory.

By default, the output is sorted alphabetically. If standard output is a terminal, the output is in columns (sorted vertically) and control characters are output as question marks; otherwise, the output is listed one per line and control characters are output as-is.

Because ls is such a fundamental program, it has accumulated many options over the years. They are described in the subsections below; within each section, options are listed alphabetically (ignoring case). The division of options into the subsections is not absolute, since some options affect more than one aspect of ls's operation.

The `-g' option is accepted but ignored, for compatibility with Unix. Also see 2. Common options.

5.1.1 Which files are listed
5.1.2 What information is listed
5.1.3 Sorting the output
5.1.4 More details about version sort
5.1.5 General output formatting
5.1.6 Formatting the file names

5.1.1 Which files are listed

These options determine which files ls lists information for. By default, any files and the contents of any directories on the command line are shown.

`-a'

`--all'

List all files in directories, including files that start with `.'.

`-A'

`--almost-all'

List all files in directories except for `.' and `..'.

`-B'

`--ignore-backups'

Do not list files that end with `~', unless they are given on the command line.

`-d'

`--directory'

List just the names of directories, as with other types of files, rather than listing their contents.

`-I PATTERN'

`--ignore=PATTERN'

Do not list files whose names match the shell pattern (not regular expression) pattern unless they are given on the command line. As in the shell, an initial `.' in a file name does not match a wildcard at the start of pattern. Sometimes it is useful to give this option several times. For example,

$ ls --ignore='.??*' --ignore='.[^.]' --ignore='#*'

The first option ignores names of length 3 or more that start with `.', the second ignores all two-character names that start with `.' except `..', and the third ignores names that start with `#'.

`-L'

`--dereference'

In a long listing, show file information (e.g., times and permissions) for the referents of symbolic links rather than for the symbolic links themselves.

`-R'

`--recursive'

List the contents of all directories recursively.

5.1.2 What information is listed

These options affect the information that ls displays. By default, only file names are shown.

`-D'

`--dired'

With the long listing (`-l') format, print an additional line after the main output:

//DIRED// beg1 end1 beg2 end2 ...

The begN and endN are unsigned integers that record the byte position of the beginning and end of each file name in the output. This makes it easy for Emacs to find the names, even when they contain unusual characters such as space or newline, without fancy searching.

If directories are being listed recursively (-R), output a similar line after each subdirectory:

//SUBDIRED// format beg1 end1 ...

Finally, output a line of the form:

//DIRED-OPTIONS// --quoting-style=word

where word is the quoting style (see section 5.1.6 Formatting the file names).

`-G'

`--no-group'

Inhibit display of group information in a long format directory listing. (This is the default in some non-GNU versions of ls, so we provide this option for compatibility.)

`-h'

`--human-readable'

Append a size letter such as `M' for megabytes to each size. Powers of 1024 are used, not 1000; `M' stands for 1,048,576 bytes. Use the `--si' option if you prefer powers of 1000.

`-H'

`--si'

Append a size letter such as `M' for megabytes to each size. (SI is the International System of Units, which defines these letters as prefixes.) Powers of 1000 are used, not 1024; `M' stands for 1,000,000 bytes. Use the `-h' or `--human-readable' option if you prefer powers of 1024.

Warning: the meaning of `-H' will change in the future to conform to POSIX. Use `--si' for the old meaning.

`-i'

`--inode'

Print the inode number (also called the file serial number and index number) of each file to the left of the file name. (This number uniquely identifies each file within a particular filesystem.)

`-l'

`--format=long'

`--format=verbose'

In addition to the name of each file, print the file type, permissions, number of hard links, owner name, group name, size in bytes, and timestamp (by default, the modification time). For files with a time more than six months old or in the future, the timestamp contains the year instead of the time of day. If the timestamp contains today's date with the year rather than a time of day, the file's time is in the future, which means you probably have clock skew problems which may break programs like make that rely on file times.

For each directory that is listed, preface the files with a line `total blocks', where blocks is the total disk allocation for all files in that directory. The block size currently defaults to 1024 bytes, but this can be overridden (see section 2.2 Block size). The blocks computed counts each hard link separately; this is arguably a deficiency.

The permissions listed are similar to symbolic mode specifications (see section 3.2 Symbolic Modes). But ls combines multiple bits into the third character of each set of permissions as follows:

`s'

If the setuid or setgid bit and the corresponding executable bit are both set.

`S'

If the setuid or setgid bit is set but the corresponding executable bit is not set.

`t'

If the sticky bit and the other-executable bit are both set.

`T'

If the sticky bit is set but the other-executable bit is not set.

`x'

If the executable bit is set and none of the above apply.

`-'

Otherwise.

Following the permission bits is a single character that specifies whether an alternate access method applies to the file. When that character is a space, there is no alternate access method. When it is a printing character (e.g., `+'), then there is such a method.

`-o'

Produce long format directory listings, but don't display group information. It is equivalent to using `--format=long' with `--no-group' . This option is provided for compatibility with other versions of ls.

`-s'

`--size'

Print the disk allocation of each file to the left of the file name. This is the amount of disk space used by the file, which is usually a bit more than the file's size, but it can be less if the file has holes.

Normally the disk allocation is printed in units of 1024 bytes, but this can be overridden (see section 2.2 Block size).

For files that are NFS-mounted from an HP-UX system to a BSD system, this option reports sizes that are half the correct values. On HP-UX systems, it reports sizes that are twice the correct values for files that are NFS-mounted from BSD systems. This is due to a flaw in HP-UX; it also affects the HP-UX ls program.

5.1.3 Sorting the output

These options change the order in which ls sorts the information it outputs. By default, sorting is done by character code (e.g., ASCII order).

`-c'

`--time=ctime'

`--time=status'

`--time=use'

If the long listing format (e.g., `-l', `-o') is being used, print the status change time (the `ctime' in the inode) instead of the modification time. When explicitly sorting by time (`--sort=time' or `-t') or when not using a long listing format, sort according to the status change time.

`-f'

Primarily, like `-U'---do not sort; list the files in whatever order they are stored in the directory. But also enable `-a' (list all files) and disable `-l', `--color', and `-s' (if they were specified before the `-f').

`-r'

`--reverse'

Reverse whatever the sorting method is--e.g., list files in reverse alphabetical order, youngest first, smallest first, or whatever.

`-S'

`--sort=size'

Sort by file size, largest first.

`-t'

`--sort=time'

Sort by modification time (the `mtime' in the inode), newest first.

`-u'

`--time=atime'

`--time=access'

If the long listing format (e.g., `--format=long') is being used, print the last access time (the `atime' in the inode). When explicitly sorting by time (`--sort=time' or `-t') or when not using a long listing format, sort according to the access time.

`-U'

`--sort=none'

Do not sort; list the files in whatever order they are stored in the directory. (Do not do any of the other unrelated things that `-f' does.) This is especially useful when listing very large directories, since not doing any sorting can be noticeably faster.

`-v'

`--sort=version'

Sort by version name and number, lowest first. It behaves like a default sort, except that each sequence of decimal digits is treated numerically as an index/version number. (See section 5.1.4 More details about version sort.)

`-X'

`--sort=extension'

Sort directory contents alphabetically by file extension (characters after the last `.'); files with no extension are sorted first.

5.1.4 More details about version sort

The version sort takes into account the fact that file names frequently include indices or version numbers. Standard sorting functions usually do not produce the ordering that people expect because comparisons are made on a character-by-character basis. The version sort addresses this problem, and is especially useful when browsing directories that contain many files with indices/version numbers in their names:

> ls -1 > ls -1v foo.zml-1.gz foo.zml-1.gz foo.zml-100.gz foo.zml-2.gz foo.zml-12.gz foo.zml-6.gz foo.zml-13.gz foo.zml-12.gz foo.zml-2.gz foo.zml-13.gz foo.zml-25.gz foo.zml-25.gz foo.zml-6.gz foo.zml-100.gz

Note also that numeric parts with leading zeroes are considered as fractional one:

> ls -1 > ls -1v abc-1.007.tgz abc-1.007.tgz abc-1.012b.tgz abc-1.01a.tgz abc-1.01a.tgz abc-1.012b.tgz

5.1.5 General output formatting

These options affect the appearance of the overall output.

`-1'

`--format=single-column'

List one file per line. This is the default for ls when standard output is not a terminal.

`-C'

`--format=vertical'

List files in columns, sorted vertically. This is the default for ls if standard output is a terminal. It is always the default for the dir and d programs. GNU ls uses variable width columns to display as many files as possible in the fewest lines.

`--color [=when]'

Specify whether to use color for distinguishing file types. when may be omitted, or one of:

• none - Do not use color at all. This is the default.
• auto - Only use color if standard output is a terminal.
• always - Always use color.

Specifying `--color' and no when is equivalent to `--color=always'. Piping a colorized listing through a pager like more or less usually produces unreadable results. However, using more -f does seem to work.

`-F'

`--classify'

`--indicator-style=classify'

Append a character to each file name indicating the file type. Also, for regular files that are executable, append `*'. The file type indicators are `/' for directories, `@' for symbolic links, `|' for FIFOs, `=' for sockets, and nothing for regular files.

`--full-time'

List times in full, rather than using the standard abbreviation heuristics. The format is currently similar to that of date, but this is planned to change in a future release, partly because modern file time stamps have more precision. It's not possible to change the format, but you can extract out the date string with cut and then pass the result to date -d. See section `date invocation' in Shell utilities.

This is most useful because the time output includes the seconds. (Unix filesystems store file timestamps only to the nearest second, so this option shows all the information there is.) For example, this can help when you have a Makefile that is not regenerating files properly.

`--indicator-style=word'

Append a character indicator with style word to entry names, as follows:

`none'

Do not append any character indicator; this is the default.

`file-type'

Append `/' for directories, `@' for symbolic links, `|' for FIFOs, `=' for sockets, and nothing for regular files. This is the same as the `-p' or `--file-type' option.

`classify'

Append `*' for executable regular files, otherwise behave as for `file-type'. This is the same as the `-F' or `--classify' option.

`-k'

`--kilobytes'

Print file sizes in 1024-byte blocks, overriding the default block size (see section 2.2 Block size).

`-m'

`--format=commas'

List files horizontally, with as many as will fit on each line, separated by `, ' (a comma and a space).

`-n'

`--numeric-uid-gid'

List the numeric UID and GID instead of the names.

`-p'

`--file-type'

`--indicator-style=file-type'

Append a character to each file name indicating the file type. This is like `-F', except that executables are not marked.

`-x format'

`--format=across'

`--format=horizontal'

List the files in columns, sorted horizontally.

`-T cols'

`--tabsize=cols'

Assume that each tabstop is cols columns wide. The default is 8. ls uses tabs where possible in the output, for efficiency. If cols is zero, do not use tabs at all.

`-w'

`--width=cols'

Assume the screen is cols columns wide. The default is taken from the terminal settings if possible; otherwise the environment variable COLUMNS is used if it is set; otherwise the default is 80.

5.1.6 Formatting the file names

These options change how file names themselves are printed.

`-b'

`--escape'

`--quoting-style=escape'

Quote nongraphic characters in file names using alphabetic and octal backslash sequences like those used in C.

`-N'

`--literal'

Do not quote file names.

`-q'

`--hide-control-chars'

Print question marks instead of nongraphic characters in file names. This is the default if the output is a terminal and the program is ls.

`-Q'

`--quote-name'

`--quoting-style=c'

Enclose file names in double quotes and quote nongraphic characters as in C.

`--quoting-style=word'

Use style word to quote output names. The word should be one of the following:

`literal'

Output names as-is.

`shell'

Quote names for the shell if they contain shell metacharacters or would cause ambiguous output.

`shell-always'

Quote names for the shell, even if they would normally not require quoting.

`c'

Quote names as for a C language string; this is the same as the `-Q' or `--quote-name' option.

`escape'

Quote as with `c' except omit the surrounding double-quote characters; this is the same as the `-b' or `--escape' option.

`clocale'

Quote as with `c' except use quotation marks appropriate for the locale.

`locale'

Like `clocale', but quote `like this' instead of "like this" in the default C locale. This looks nicer on many displays.

You can specify the default value of the `--quoting-style' option with the environment variable QUOTING_STYLE. If that environment variable is not set, the default value is `literal', but this default may change to `shell' in a future version of this package.

`--show-control-chars'

Print nongraphic characters as-is in file names. This is the default unless the output is a terminal and the program is ls.

5.2 dir: Briefly list directory contents

dir (also installed as d) is equivalent to ls -C -b; that is, by default files are listed in columns, sorted vertically, and special characters are represented by backslash escape sequences.

See section ls.

5.3 vdir: Verbosely list directory contents

vdir (also installed as v) is equivalent to ls -l -b; that is, by default files are listed in long format and special characters are represented by backslash escape sequences.

5.4 dircolors: Color setup for ls

dircolors outputs a sequence of shell commands to set up the terminal for color output from ls (and dir, etc.). Typical usage:

eval `dircolors [option]... [file]`

If file is specified, dircolors reads it to determine which colors to use for which file types and extensions. Otherwise, a precompiled database is used. For details on the format of these files, run `dircolors --print-database'.

The output is a shell command to set the LS_COLORS environment variable. You can specify the shell syntax to use on the command line, or dircolors will guess it from the value of the SHELL environment variable.

The program accepts the following options. Also see 2. Common options.

`-b'

`--sh'

`--bourne-shell'

Output Bourne shell commands. This is the default if the SHELL environment variable is set and does not end with `csh' or `tcsh'.

`-c'

`--csh'

`--c-shell'

Output C shell commands. This is the default if SHELL ends with csh or tcsh.

`-p'

`--print-database'

Print the (compiled-in) default color configuration database. This output is itself a valid configuration file, and is fairly descriptive of the possibilities.

6. Basic operations

This chapter describes the commands for basic file manipulation: copying, moving (renaming), and deleting (removing).

6.1 cp: Copy files and directories		Copy files.
6.2 dd: Convert and copy a file		Convert and copy a file.
6.3 install: Copy files and set attributes		Copy files and set attributes.
6.4 mv: Move (rename) files		Move (rename) files.
6.5 rm: Remove files or directories		Remove files or directories.
6.6 shred: Remove files more securely		Remove files more securely.

6.1 cp: Copy files and directories

cp copies files (or, optionally, directories). The copy is completely independent of the original. You can either copy one file to another, or copy arbitrarily many files to a destination directory. Synopsis:

cp [option]... source dest cp [option]... source... directory

If the last argument names an existing directory, cp copies each source file into that directory (retaining the same name). Otherwise, if only two files are given, it copies the first onto the second. It is an error if the last argument is not a directory and more than two non-option arguments are given.

Generally, files are written just as they are read. For exceptions, see the `--sparse' option below.

By default, cp does not copy directories. However, the `-R', `-a', and `-r' options cause cp to copy recursively by descending into source directories and copying files to corresponding destination directories.

By default, cp follows symbolic links only when not copying recursively. This default can be overridden with the `--no-dereference' (`-d'), `--dereference' (`-L'), and `-H' options. If more than one of these options is specified, the last one silently overrides the others.

cp generally refuses to copy a file onto itself, with the following exception: if `--force --backup' is specified with source and dest identical, and referring to a regular file, cp will make a backup file, either regular or numbered, as specified in the usual ways (see section 2.1 Backup options). This is useful when you simply want to make a backup of an existing file before changing it.

The program accepts the following options. Also see 2. Common options.

`-a'

`--archive'

Preserve as much as possible of the structure and attributes of the original files in the copy (but do not attempt to preserve internal directory structure; i.e., `ls -U' may list the entries in a copied directory in a different order). Equivalent to `-dpR'.

`-b'

`--backup[=method]'

See section 2.1 Backup options. Make a backup of each file that would otherwise be overwritten or removed. As a special case, cp makes a backup of source when the force and backup options are given and source and dest are the same name for an existing, regular file. One useful application of this combination of options is this tiny Bourne shell script:

#!/bin/sh # Usage: backup FILE... # Create a GNU-style backup of each listed FILE. for i in "$@"; do cp --backup --force "$i" "$i" done

`-d'

`--no-dereference'

Copy symbolic links as symbolic links rather than copying the files that they point to, and preserve hard links between source files in the copies.

`-f'

`--force'

When copying without this option and an existing destination file cannot be opened for writing, the copy fails. However, with `--force'), when a destination file cannot be opened, cp then unlinks it and tries to open it again. Contrast this behavior with that enabled by `--link' and `--symbolic-link', whereby the destination file is never opened but rather is unlinked unconditionally. Also see the description of `--remove-destination'.

`-H'

If a command line argument specifies a symbolic link, then copy the file it points to rather than the symbolic link itself. However, copy (preserving its nature) a