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Extensions over GNU

Though the main goal of the project is compatibility, uutils supports a few features that are not supported by GNU coreutils. We take care not to introduce features that are incompatible with the GNU coreutils. Below is a list of uutils extensions.

General

GNU coreutils provides two ways to define short options taking an argument:

$ ls -w 80
$ ls -w80

We support a third way:

$ ls -w=80

env

GNU env allows the empty string to be used as an environment variable name. This is unsupported by uutils, and it will show a warning on any such assignment.

env has an additional -f/--file flag that can parse .env files and set variables accordingly. This feature is adopted from dotenv style packages.

cp

cp can display a progress bar when the -g/--progress flag is set.

mv

mv can display a progress bar when the -g/--progress flag is set.

hashsum

This utility does not exist in GNU coreutils. hashsum is a utility that supports computing the checksums with several algorithms. The flags and options are identical to the *sum family of utils (sha1sum, sha256sum, b2sum, etc.).

b3sum

This utility does not exist in GNU coreutils. The behavior is modeled after both the b2sum utility of GNU and the b3sum utility by the BLAKE3 team and supports the --no-names option that does not appear in the GNU util.

more

We provide a simple implementation of more, which is not part of GNU coreutils. We do not aim for full compatibility with the more utility from util-linux. Features from more modern pagers (like less and bat) are therefore welcomed.

cut

cut can separate fields by whitespace (Space and Tab) with -w flag. This feature is adopted from FreeBSD.

fmt

fmt has additional flags for prefixes: -P/--skip-prefix, -x/--exact-prefix, and -X/--exact-skip-prefix. With -m/--preserve-headers, an attempt is made to detect and preserve mail headers in the input. -q/--quick breaks lines more quickly. And -T/--tab-width defines the number of spaces representing a tab when determining the line length.

printf

printf uses arbitrary precision decimal numbers to parse and format floating point numbers. GNU coreutils uses long double, whose actual size may be double precision 64-bit float (e.g 32-bit arm), extended precision 80-bit float (x86(-64)), or quadruple precision 128-bit float (e.g. arm64).

Practically, this means that printing a number with a large precision will stay exact:

printf "%.48f\n" 0.1
0.100000000000000000000000000000000000000000000000 << uutils on all platforms
0.100000000000000000001355252715606880542509316001 << GNU coreutils on x86(-64)
0.100000000000000000000000000000000004814824860968 << GNU coreutils on arm64
0.100000000000000005551115123125782702118158340454 << GNU coreutils on armv7 (32-bit)

Hexadecimal floats

For hexadecimal float format (%a), POSIX only states that one hexadecimal number should be present left of the decimal point (0xh.hhhhp±d [1]), but does not say how many bits should be included (between 1 and 4). On x86(-64), the first digit always includes 4 bits, so its value is always between 0x8 and 0xf, while on other architectures, only 1 bit is included, so the value is always 0x1.

However, the first digit will of course be 0x0 if the number is zero. Also, rounding numbers may cause the first digit to be 0x1 on x86(-64) (e.g. 0xf.fffffffp-5 rounds to 0x1.00p-1), or 0x2 on other architectures.

We chose to replicate x86-64 behavior on all platforms.

Additionally, the default precision of the hexadecimal float format (%a without any specifier) is expected to be "sufficient for exact representation of the value" [1]. This is not possible in uutils as we store arbitrary precision numbers that may be periodic in hexadecimal form (0.1 = 0xc.ccc...p-7), so we revert to the number of digits that would be required to exactly print an extended precision 80-bit float, emulating GNU coreutils behavior on x86(-64). An 80-bit float has 64 bits in its integer and fractional part, so 16 hexadecimal digits are printed in total (1 digit before the decimal point, 15 after).

Practically, this means that the default hexadecimal floating point output is identical to x86(-64) GNU coreutils:

printf "%a\n" 0.1
0xc.ccccccccccccccdp-7 << uutils on all platforms
0xc.ccccccccccccccdp-7 << GNU coreutils on x86-64
0x1.999999999999999999999999999ap-4 << GNU coreutils on arm64
0x1.999999999999ap-4   << GNU coreutils on armv7 (32-bit)

We can print an arbitrary number of digits if a larger precision is requested, and the leading digit will still be in the 0x8-0xf range:

printf "%.32a\n" 0.1
0xc.cccccccccccccccccccccccccccccccdp-7 << uutils on all platforms
0xc.ccccccccccccccd00000000000000000p-7 << GNU coreutils on x86-64
0x1.999999999999999999999999999a0000p-4 << GNU coreutils on arm64
0x1.999999999999a0000000000000000000p-4 << GNU coreutils on armv7 (32-bit)

Note: The architecture-specific behavior on non-x86(-64) platforms may change in the future.

seq

Unlike GNU coreutils, seq always uses arbitrary precision decimal numbers, no matter the parameters (integers, decimal numbers, positive or negative increments, format specified, etc.), so its output will be more correct than GNU coreutils for some inputs (e.g. small fractional increments where GNU coreutils uses long double).

The only limitation is that the position of the decimal point is stored in a i64, so values smaller than 10**(-263) will underflow to 0, and some values larger than 10(2**63) may overflow to infinity.

See also comments under printf for formatting precision and differences.

seq provides -t/--terminator to set the terminator character.

sort

When sorting with -g/--general-numeric-sort, arbitrary precision decimal numbers are parsed and compared, unlike GNU coreutils that uses platform-specific long double floating point numbers.

Extremely large or small values can still overflow or underflow to infinity or zero, see note in seq.

ls

GNU ls provides two ways to use a long listing format: -l and --format=long. We support a third way: --long.

GNU ls --sort=VALUE only supports special non-default sort orders. We support --sort=name, which makes it possible to override an earlier value.

du

du allows birth and creation as values for the --time argument to show the creation time. It also provides a -v/--verbose flag.

id

id has three additional flags:

  • -P displays the id as a password file entry
  • -p makes the output human-readable
  • -A displays the process audit user ID

uptime

Similar to the proc-ps implementation and unlike GNU/Coreutils, uptime provides -s/--since to show since when the system is up.

base32/base64/basenc

Just like on macOS, base32/base64/basenc provides -D to decode data.

shred

The number of random passes is deterministic in both GNU and uutils. However, uutils shred computes the number of random passes in a simplified way, specifically max(3, x / 10), which is very close but not identical to the number of random passes that GNU would do. This also satisfies an expectation that reasonable users might have, namely that the number of random passes increases monotonically with the number of passes overall; GNU shred violates this assumption.

unexpand

GNU unexpand provides --first-only to convert only leading sequences of blanks. We support a second way: -f like busybox.

Using -U/--no-utf8, you can interpret input files as 8-bit ASCII rather than UTF-8.

expand

expand also offers the -U/--no-utf8 option to interpret input files as 8-bit ASCII instead of UTF-8.