Originální popis anglicky:
cut - cut out selected fields of each line of a file
Návod, kniha: POSIX Programmer's Manual
cut -b list [-n] [file
...]
cut -c
list [file
...]
cut -f
list [-d
delim][-s][file
...]
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.
The
cut utility shall conform to the Base Definitions volume of
IEEE Std 1003.1-2001, 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 (
low-
high), which represents all fields from the first number to
the second number. The second is a positive number preceded by a hyphen (-
high), which represents all fields from field number 1 to that number.
The third is a positive number followed by a hyphen (
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-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.
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.
The standard input shall be used only if no
file operands are specified,
or if a
file operand is
'-' . See the INPUT FILES section.
The input files shall be text files, except that line lengths shall be
unlimited.
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
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_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 .
Default.
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>
The standard error shall be used only for diagnostic messages.
None.
None.
The following exit values shall be returned:
- 0
- All input files were output successfully.
- >0
- An error occurred.
Default.
The following sections are informative.
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.)
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 IEEE Std 1003.1-2001 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
Some historical implementations do not count <backspace>s 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>s or <tab>s
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
IEEE Std 1003.1-2001, 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
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.
None.
grep ,
paste ,
Parameters and Variables
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
.
