coreutils.texi

Linux下文件工具。

@cindex mebibyte, definition of
mebibyte: @math{2^20 = 1,048,576}.
@item GB
@cindex gigabyte, definition of
gigabyte: @math{10^9 = 1,000,000,000}.
@item G
@itemx GiB
@cindex gibibyte, definition of
gibibyte: @math{2^30 = 1,073,741,824}.
@item TB
@cindex terabyte, definition of
terabyte:  @math{10^12 = 1,000,000,000,000}.
@item T
@itemx TiB
@cindex tebibyte, definition of
tebibyte: @math{2^40 = 1,099,511,627,776}.
@item PB
@cindex petabyte, definition of
petabyte: @math{10^15 = 1,000,000,000,000,000}.
@item P
@itemx PiB
@cindex pebibyte, definition of
pebibyte: @math{2^50 = 1,125,899,906,842,624}.
@item EB
@cindex exabyte, definition of
exabyte: @math{10^18 = 1,000,000,000,000,000,000}.
@item E
@itemx EiB
@cindex exbibyte, definition of
exbibyte: @math{2^60 = 1,152,921,504,606,846,976}.
@item ZB
@cindex zettabyte, definition of
zettabyte: @math{10^21 = 1,000,000,000,000,000,000,000}
@item Z
@itemx ZiB
@math{2^70 = 1,180,591,620,717,411,303,424}.
(@samp{Zi} is a GNU extension to IEC 60027-2.)
@item YB
@cindex yottabyte, definition of
yottabyte: @math{10^24 = 1,000,000,000,000,000,000,000,000}.
@item Y
@itemx YiB
@math{2^80 = 1,208,925,819,614,629,174,706,176}.
(@samp{Yi} is a GNU extension to IEC 60027-2.)
@end table

@opindex -k
@opindex -h
@opindex --block-size
@opindex --human-readable
@opindex --si

Block size defaults can be overridden by an explicit
@option{--block-size=@var{size}} option.  The @option{-k}
option is equivalent to @option{--block-size=1K}, which
is the default unless the @env{POSIXLY_CORRECT} environment variable is
set.  The @option{-h} or @option{--human-readable} option is equivalent to
@option{--block-size=human-readable}.  The @option{--si} option is
equivalent to @option{--block-size=si}.

@node Target directory
@section Target directory

@cindex target directory

Some @sc{gnu} programs (at least @command{cp}, @code{install}, @code{ln}, and
@command{mv}) allow you to specify the target directory via this option:

@table @samp

@itemx @w{@kbd{--target-directory}=@var{directory}}
@opindex --target-directory
@cindex target directory
@cindex destination directory
Specify the destination @var{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 @code{xargs}
program is designed to work well with this convention.

The commands in the @command{mv}-family are unusual in that they take
a variable number of arguments with a special case at the @emph{end}
(namely, the target directory).  This makes it nontrivial to perform some
operations, e.g., ``move all files from here to ../d/'', because
@code{mv * ../d/} might exhaust the argument space, and @code{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 @w{@kbd{--target-directory}} option allows the @command{cp},
@command{install}, @code{ln}, and @code{mv} programs to be used conveniently
with @code{xargs}.  For example, you can move the files from the
current directory to a sibling directory, @code{d} like this:
(However, this doesn't move files whose names begin with @samp{.}.)

@smallexample
ls |xargs mv --target-directory=../d
@end smallexample

If you use the @sc{gnu} @code{find} program, you can move @emph{all}
files with this command:
@example
find . -mindepth 1 -maxdepth 1 \
  | xargs mv --target-directory=../d
@end example

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
@sc{gnu} @code{find} and @sc{gnu} @code{xargs}:
@example
find . -mindepth 1 -maxdepth 1 -print0 \
  | xargs --null --no-run-if-empty \
      mv --target-directory=../d
@end example

@end table

@node Trailing slashes
@section Trailing slashes

@cindex trailing slashes

Some @sc{gnu} programs (at least @command{cp} and @code{mv}) allow you to
remove any trailing slashes from each @var{source} argument before
operating on it.  The @w{@kbd{--strip-trailing-slashes}} option enables
this behavior.

This is useful when a @var{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, @command{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 @emph{directory} and not
the symbolic link.  Although it may seem surprising that such behavior
be the default, it is required by @acronym{POSIX} and is consistent with
other parts of that standard.

@node Standards conformance
@section Standards conformance

@vindex POSIXLY_CORRECT
In a few cases, the @sc{gnu} utilities' default behavior is
incompatible with the @acronym{POSIX} standard.  To suppress these
incompatibilities, define the @env{POSIXLY_CORRECT} environment
variable.  Unless you are checking for @acronym{POSIX} conformance, you
probably do not need to define @env{POSIXLY_CORRECT}.

Newer versions of @acronym{POSIX} are occasionally incompatible with older
versions.  For example, older versions of @acronym{POSIX} required the
command @samp{sort +1} to sort based on the second and succeeding
fields in each input line, but starting with @acronym{POSIX} 1003.1-2001
the same command is required to sort the file named @file{+1}, and you
must instead use the command @samp{sort -k 2} to get the field-based
sort.

@vindex _POSIX2_VERSION
The @sc{gnu} utilities normally conform to the version of @acronym{POSIX}
that is standard for your system.  To cause them to conform to a
different version of @acronym{POSIX}, define the @env{_POSIX2_VERSION}
environment variable to a value of the form @var{yyyymm} specifying
the year and month the standard was adopted.  Two values are currently
supported for @env{_POSIX2_VERSION}: @samp{199209} stands for
@acronym{POSIX} 1003.2-1992, and @samp{200112} stands for @acronym{POSIX}
1003.1-2001.  For example, if you are running older software that
assumes an older version of @acronym{POSIX} and uses @samp{sort +1}, you
can work around the compatibility problems by setting
@samp{_POSIX2_VERSION=199209} in your environment.

@node Output of entire files
@chapter Output of entire files

@cindex output of entire files
@cindex entire files, output of

These commands read and write entire files, possibly transforming them
in some way.

@menu
* cat invocation::              Concatenate and write files.
* tac invocation::              Concatenate and write files in reverse.
* nl invocation::               Number lines and write files.
* od invocation::               Write files in octal or other formats.
@end menu

@node cat invocation
@section @command{cat}: Concatenate and write files

@pindex cat
@cindex concatenate and write files
@cindex copying files

@command{cat} copies each @var{file} (@samp{-} means standard input), or
standard input if none are given, to standard output.  Synopsis:

@example
cat [@var{option}] [@var{file}]@dots{}
@end example

The program accepts the following options.  Also see @ref{Common options}.

@table @samp

@item -A
@itemx --show-all
@opindex -A
@opindex --show-all
Equivalent to @option{-vET}.

@item -B
@itemx --binary
@opindex -B
@opindex --binary
@cindex binary and text I/O in cat
On MS-DOS and MS-Windows only, read and write the files in binary mode.
By default, @command{cat} on MS-DOS/MS-Windows uses binary mode only when
standard output is redirected to a file or a pipe; this option overrides
that.  Binary file I/O is used so that the files retain their format
(Unix text as opposed to DOS text and binary), because @command{cat} is
frequently used as a file-copying program.  Some options (see below)
cause @command{cat} to read and write files in text mode because in those
cases the original file contents aren't important (e.g., when lines are
numbered by @command{cat}, or when line endings should be marked).  This is
so these options work as DOS/Windows users would expect; for example,
DOS-style text files have their lines end with the CR-LF pair of
characters, which won't be processed as an empty line by @option{-b} unless
the file is read in text mode.

@item -b
@itemx --number-nonblank
@opindex -b
@opindex --number-nonblank
Number all nonblank output lines, starting with 1.  On MS-DOS and
MS-Windows, this option causes @command{cat} to read and write files in
text mode.

@item -e
@opindex -e
Equivalent to @option{-vE}.

@item -E
@itemx --show-ends
@opindex -E
@opindex --show-ends
Display a @samp{$} after the end of each line.  On MS-DOS and
MS-Windows, this option causes @command{cat} to read and write files in
text mode.

@item -n
@itemx --number
@opindex -n
@opindex --number
Number all output lines, starting with 1.  On MS-DOS and MS-Windows,
this option causes @command{cat} to read and write files in text mode.

@item -s
@itemx --squeeze-blank
@opindex -s
@opindex --squeeze-blank
@cindex squeezing blank lines
Replace multiple adjacent blank lines with a single blank line.  On
MS-DOS and MS-Windows, this option causes @command{cat} to read and write
files in text mode.

@item -t
@opindex -t
Equivalent to @option{-vT}.

@item -T
@itemx --show-tabs
@opindex -T
@opindex --show-tabs
Display TAB characters as @samp{^I}.

@item -u
@opindex -u
Ignored; for Unix compatibility.

@item -v
@itemx --show-nonprinting
@opindex -v
@opindex --show-nonprinting
Display control characters except for LFD and TAB using
@samp{^} notation and precede characters that have the high bit set with
@samp{M-}.  On MS-DOS and MS-Windows, this option causes @command{cat} to
read files and standard input in DOS binary mode, so the CR
characters at the end of each line are also visible.

@end table


@node tac invocation
@section @command{tac}: Concatenate and write files in reverse

@pindex tac
@cindex reversing files

@command{tac} copies each @var{file} (@samp{-} means standard input), or
standard input if none are given, to standard output, reversing the
records (lines by default) in each separately.  Synopsis:

@example
tac [@var{option}]@dots{} [@var{file}]@dots{}
@end example

@dfn{Records} are separated by instances of a string (newline by
default).  By default, this separator string is attached to the end of
the record that it follows in the file.

The program accepts the following options.  Also see @ref{Common options}.

@table @samp

@item -b
@itemx --before
@opindex -b
@opindex --before
The separator is attached to the beginning of the record that it
precedes in the file.

@item -r
@itemx --regex
@opindex -r
@opindex --regex
Treat the separator string as a regular expression.  Users of @command{tac}
on MS-DOS/MS-Windows should note that, since @command{tac} reads files in
binary mode, each line of a text file might end with a CR/LF pair
instead of the Unix-style LF.

@item -s @var{separator}
@itemx --separator=@var{separator}
@opindex -s
@opindex --separator
Use @var{separator} as the record separator, instead of newline.

@end table


@node nl invocation
@section @command{nl}: Number lines and write files

@pindex nl
@cindex numbering lines
@cindex line numbering

@command{nl} writes each @var{file} (@samp{-} means standard input), or
standard input if none are given, to standard output, with line numbers
added to some or all of the lines.  Synopsis:

@example
nl [@var{option}]@dots{} [@var{file}]@dots{}
@end example

@cindex logical pages, numbering on
@command{nl} decomposes its input into (logical) pages; by default, the
line number is reset to 1 at the top of each logical page.  @command{nl}
treats all of the input files as a single document; it does not reset