вырезать выбранные поля каждой строки файла (cut out selected fields of each line of a file)
Пролог (Prolog)
This manual page is part of the POSIX Programmer's Manual. The
Linux implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
Имя (Name)
cut — cut out selected fields of each line of a file
Синопсис (Synopsis)
cut -b list [-n] [file...]
cut -c list [file...]
cut -f list [-d delim] [-s] [file...]
Описание (Description)
The cut utility shall cut out bytes (-b option), characters (-c
option), or character-delimited fields (-f option) from each line
in one or more files, concatenate them, and write them to
standard output.
Параметры (Options)
The cut utility shall conform to the Base Definitions volume of
POSIX.1‐2017, Section 12.2, Utility Syntax Guidelines.
The application shall ensure that the option-argument list (see
options -b, -c, and -f below) is a <comma>-separated list or
<blank>-separated list of positive numbers and ranges. Ranges can
be in three forms. The first is two positive numbers separated by
a <hyphen-minus> (low-high), which represents all fields from the
first number to the second number. The second is a positive
number preceded by a <hyphen-minus> (-high), which represents all
fields from field number 1 to that number. The third is a
positive number followed by a <hyphen-minus> (low-), which
represents that number to the last field, inclusive. The elements
in list can be repeated, can overlap, and can be specified in any
order, but the bytes, characters, or fields selected shall be
written in the order of the input data. If an element appears in
the selection list more than once, it shall be written exactly
once.
The following options shall be supported:
-b list Cut based on a list of bytes. Each selected byte shall
be output unless the -n option is also specified. It
shall not be an error to select bytes not present in
the input line.
-c list Cut based on a list of characters. Each selected
character shall be output. It shall not be an error to
select characters not present in the input line.
-d delim Set the field delimiter to the character delim. The
default is the <tab>.
-f list Cut based on a list of fields, assumed to be separated
in the file by a delimiter character (see -d). Each
selected field shall be output. Output fields shall be
separated by a single occurrence of the field delimiter
character. Lines with no field delimiters shall be
passed through intact, unless -s is specified. It shall
not be an error to select fields not present in the
input line.
-n Do not split characters. When specified with the -b
option, each element in list of the form low-high
(<hyphen-minus>-separated numbers) shall be modified as
follows:
* If the byte selected by low is not the first byte
of a character, low shall be decremented to select
the first byte of the character originally selected
by low. If the byte selected by high is not the
last byte of a character, high shall be decremented
to select the last byte of the character prior to
the character originally selected by high, or zero
if there is no prior character. If the resulting
range element has high equal to zero or low greater
than high, the list element shall be dropped from
list for that input line without causing an error.
Each element in list of the form low- shall be treated
as above with high set to the number of bytes in the
current line, not including the terminating <newline>.
Each element in list of the form -high shall be treated
as above with low set to 1. Each element in list of the
form num (a single number) shall be treated as above
with low set to num and high set to num.
-s Suppress lines with no delimiter characters, when used
with the -f option. Unless specified, lines with no
delimiters shall be passed through untouched.
Операнды (Operands)
The following operand shall be supported:
file A pathname of an input file. If no file operands are
specified, or if a file operand is '-', the standard
input shall be used.
Стандартный ввод (Stdin)
The standard input shall be used only if no file operands are
specified, or if a file operand is '-'. See the INPUT FILES
section.
Входные файлы (Input files)
The input files shall be text files, except that line lengths
shall be unlimited.
Переменные окружения (Environment variables)
The following environment variables shall affect the execution of
cut:
LANG Provide a default value for the internationalization
variables that are unset or null. (See the Base
Definitions volume of POSIX.1‐2017, 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_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 input files).
LC_MESSAGES
Determine the locale that should be used to affect the
format and contents of diagnostic messages written to
standard error.
NLSPATH Determine the location of message catalogs for the
processing of LC_MESSAGES.
Асинхронные события (Asynchronous events)
Default.
Стандартный вывод (Stdout)
The cut utility output shall be a concatenation of the selected
bytes, characters, or fields (one of the following):
"%s\n", <concatenation of bytes>
"%s\n", <concatenation of characters>
"%s\n", <concatenation of fields and field delimiters>
Стандартный вывод сообщений (Stderr)
The standard error shall be used only for diagnostic messages.
Выходные файлы (Output files)
None.
Расширенное описание (Extended description)
None.
Статус выхода (Exit)
The following exit values shall be returned:
0 All input files were output successfully.
>0 An error occurred.
Последствия ошибок (Consequences of errors)
Default.
The following sections are informative.
Использование в приложениях (Application usage)
The cut and fold utilities can be used to create text files out
of files with arbitrary line lengths. The cut utility should be
used when the number of lines (or records) needs to remain
constant. The fold utility should be used when the contents of
long lines need to be kept contiguous.
Earlier versions of the cut utility worked in an environment
where bytes and characters were considered equivalent (modulo
<backspace> and <tab> processing in some implementations). In the
extended world of multi-byte characters, the new -b option has
been added. The -n option (used with -b) allows it to be used to
act on bytes rounded to character boundaries. The algorithm
specified for -n guarantees that:
cut -b 1-500 -n file > file1
cut -b 501- -n file > file2
ends up with all the characters in file appearing exactly once in
file1 or file2. (There is, however, a <newline> in both file1
and file2 for each <newline> in file.)
Примеры (Examples)
Examples of the option qualifier list:
1,4,7 Select the first, fourth, and seventh bytes, characters,
or fields and field delimiters.
1-3,8 Equivalent to 1,2,3,8.
-5,10 Equivalent to 1,2,3,4,5,10.
3- Equivalent to third to last, inclusive.
The low-high forms are not always equivalent when used with -b
and -n and multi-byte characters; see the description of -n.
The following command:
cut -d : -f 1,6 /etc/passwd
reads the System V password file (user database) and produces
lines of the form:
<user ID>:<home directory>
Most utilities in this volume of POSIX.1‐2017 work on text files.
The cut utility can be used to turn files with arbitrary line
lengths into a set of text files containing the same data. The
paste utility can be used to create (or recreate) files with
arbitrary line lengths. For example, if file contains long lines:
cut -b 1-500 -n file > file1
cut -b 501- -n file > file2
creates file1 (a text file) with lines no longer than 500 bytes
(plus the <newline>) and file2 that contains the remainder of the
data from file. (Note that file2 is not a text file if there are
lines in file that are longer than 500 + {LINE_MAX} bytes.) The
original file can be recreated from file1 and file2 using the
command:
paste -d "\0" file1 file2 > file
Обоснование (Rationale)
Some historical implementations do not count <backspace>
characters in determining character counts with the -c option.
This may be useful for using cut for processing nroff output. It
was deliberately decided not to have the -c option treat either
<backspace> or <tab> characters in any special fashion. The fold
utility does treat these characters specially.
Unlike other utilities, some historical implementations of cut
exit after not finding an input file, rather than continuing to
process the remaining file operands. This behavior is prohibited
by this volume of POSIX.1‐2017, where only the exit status is
affected by this problem.
The behavior of cut when provided with either mutually-exclusive
options or options that do not work logically together has been
deliberately left unspecified in favor of global wording in
Section 1.4, Utility Description Defaults.
The OPTIONS section was changed in response to IEEE PASC
Interpretation 1003.2 #149. The change represents historical
practice on all known systems. The original standard was
ambiguous on the nature of the output.
The list option-arguments are historically used to select the
portions of the line to be written, but do not affect the order
of the data. For example:
echo abcdefghi | cut -c6,2,4-7,1
yields "abdefg".
A proposal to enhance cut with the following option:
-o Preserve the selected field order. When this option is
specified, each byte, character, or field (or ranges of
such) shall be written in the order specified by the list
option-argument, even if this requires multiple outputs of
the same bytes, characters, or fields.
was rejected because this type of enhancement is outside the
scope of the IEEE P1003.2b draft standard.
Будущие направления (Future directions)
None.
Смотри также (See also)
Section 2.5, Parameters and Variables, fold(1p), grep(1p),
paste(1p)
The Base Definitions volume of POSIX.1‐2017, Chapter 8,
Environment Variables, Section 12.2, Utility Syntax Guidelines
