CUT(1POSIX)

📦 version 2017a, in debian bookworm, debian trixie, ubuntu jammy, ubuntu noble, ubuntu resolute, ubuntu stonking

💖 CUT(1POSIX) 💖

okay bestie, so this one is from the POSIX Programmer's Manual — it's literally the spec page for cut, the utility that ✨cuts stuff out of lines✨. Heads up though:

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.

🌸 NAME 🌸

cut — cut out selected fields of each line of a file

✨ SYNOPSIS ✨

cut -b list [-n] [file...]

cut -c list [file...]

cut -f list [-d delim] [-s] [file...]

🦋 DESCRIPTION 🦋

So cut shall slice out bytes (that's the -b option), characters (that's -c), or character-delimited fields (that's -f) from every single line in one or more files, smoosh them all together, and write the result to standard output. it's giving scissors but make it text processing 💅

🎀 OPTIONS 🎀

cut shall conform to the Base Definitions volume of POSIX.1‐2017, Section 12.2, Utility Syntax Guidelines. periodt.

The application shall ensure that the option-argument list (see the -b, -c, and -f options below) is a <comma>-separated list or <blank>-separated list of positive numbers and ranges. Ranges come in three forms, bestie:

  1. Two positive numbers separated by a <hyphen-minus> (low-high) — that's everything from the first number to the second number, inclusive.
  2. A positive number preceded by a <hyphen-minus> (-high) — that's everything from field number 1 up to that number.
  3. A positive number followed by a <hyphen-minus> (low-) — that's that number all the way to the last field, inclusive.

The elements in list can be repeated, can overlap, and can be specified in any order — no rules, we're feral — but the bytes, characters, or fields that get selected shall be written in the order of the input data. If an element shows up in the selection list more than once, it shall be written exactly once. no duplicates, we said what we said.

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>. (iconic default ngl)
  • -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.

🍓 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.

🌈 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.

🧚 INPUT FILES 🧚

The input files shall be text files, except that line lengths shall be unlimited. yes bestie, go absolutely wild with those line lengths.

💜 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.

💅 ASYNCHRONOUS EVENTS 💅

Default. nothing to see here, moving on ✨

⭐ 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>

🌸 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:

  1. 0 — All input files were output successfully.
  2. >0 — An error occurred.

💀 CONSEQUENCES OF ERRORS 💀

Default.

The following sections are informative.

🔥 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. iykyk ✨

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.) no cap, that's literally the guarantee.

🌈 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. (not me warning you twice 💀)

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

💜 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". wild, right? the order in the list literally does not matter bestie.

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. rip -o, you would've slayed 😭

🧚 FUTURE DIRECTIONS 🧚

None.

⭐ SEE ALSO ⭐

Section 2.5, Parameters and Variables, fold, grep, paste

The Base Definitions volume of POSIX.1‐2017, Chapter 8, Environment Variables, Section 12.2, Utility Syntax Guidelines

okay bestie, legal era incoming, but it's actually important so stay with me 🫶

Some of this text is reprinted and reproduced in electronic form, pulled straight from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, and the copyright on that is held by the Institute of Electrical and Electronics Engineers, Inc and The Open Group, (C) 2018. slay, iconic, legally binding 💅

And here's the vibe check that matters: if this version and the original IEEE and The Open Group Standard ever disagree? the original IEEE and The Open Group Standard is the referee document. like, it wins, no debate, periodt. You can get the original Standard online at http://www.opengroup.org/unix/online.html ✨

ngl, any typographical or formatting errors you spot in this page are most likely little gremlins that snuck in during the conversion of the source files into man page format 🙈 To report those errors, go to https://www.kernel.org/doc/man-pages/reporting_bugs.html.

and that's a wrap on the whole page bestie!! 🎀 this one came to you from IEEE/The Open Group, dated 2017, and it's the man page for CUT(1POSIX) 💖 go forth and slice those lines, you absolute icon 👑

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