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A page for each applet in the kit, plus .so stubs for aliases such as egrep and unxz. Each was written from the pinned busybox-w32 source with the kit's patches and configuration, then checked against the source and by experiment. The NOTES sections cover Windows behavior. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
176 lines
4.1 KiB
Groff
176 lines
4.1 KiB
Groff
.TH FACTOR 1 2026-10-19 "w64devkit" "w64devkit Manual"
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.SH NAME
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factor \- print the prime factors of integers
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.SH SYNOPSIS
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.B factor
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.RI [ number ...]
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.SH DESCRIPTION
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.B factor
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writes the prime factorization of each
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.IR number ,
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or, with no operands, of each number on standard input.
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Standard input is read to the end of the file.
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Each line holds any number of numbers, separated by white space, and
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blank lines are ignored.
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With operands, standard input is not read.
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.PP
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Each
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.I number
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is a decimal integer from 0 to
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.BR 18446744073709551615 ,
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which is 2^64 \- 1.
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It may start with a plus sign, and an operand may have white space
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before that.
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A leading zero does not make a number octal:
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.B 010
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is ten.
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Anything else is invalid: a minus sign, a
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.B 0x
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prefix, an exponent or a fraction, other text after the digits (even
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white space, in an operand), an empty operand, or a value above the
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maximum.
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.PP
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The results are written to standard output in input order, one line per
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number.
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Each line has the number, a colon, and the prime factors in ascending
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order, each after a space.
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A prime that divides the number several times is repeated.
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A prime is its own only factor, and 0 and 1 have none, so their lines
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end after the colon.
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The number is written in plain decimal, without a plus sign or leading
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zeros.
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.PP
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On an invalid number,
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.B factor
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writes a usage message on standard error and exits with status 1.
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The results for the numbers before it are still written, and the
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numbers after it are not examined.
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The message does not say which number is at fault.
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.SH OPTIONS
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.B factor
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has no options.
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Apart from a first argument of
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.BR \-\-help ,
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an argument that begins with a dash is an invalid number, and
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.B \-\-
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is not special.
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.TP
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.B \-\-help
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Print the busybox version and a usage message on standard output, and
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exit with status 0.
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It is recognized only as the first argument, and any further arguments
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are then ignored.
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In any other position it is an invalid number.
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.SH ENVIRONMENT
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.TP
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.B BB_GLOBBING
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Unless it is
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.BR 0 ,
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wildcards in the operands are expanded when
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.B factor
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starts, as needed when run from
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.BR cmd.exe .
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A busybox process started with it unset sets it to
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.B 0
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for its children, so commands run from the kit's shell receive their
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operands as the shell expanded them.
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.PP
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Every applet also reads
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.B BB_CRITICAL_ERROR_DIALOGS
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and
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.B BB_UMASK
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at startup, and
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.BR BB_SKIP_ANSI_EMULATION ,
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.BR BB_TERMINAL_MODE ,
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.BR CONEMUPID ,
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.BR LANG ,
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.BR LC_ALL ,
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and
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.B LC_CTYPE
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when writing to a console.
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None of these changes what
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.B factor
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writes.
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They are described in
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.BR busybox (1).
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.SH EXIT STATUS
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.TP
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.B 0
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Success, including an empty input, or a first argument of
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.BR \-\-help .
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.TP
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.B 1
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An invalid number, with a usage message on standard error.
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.TP
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.B 141
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Standard output is a pipe whose reader has exited, found when a write
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fails.
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No message is printed.
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.SH EXAMPLES
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Factor a number:
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.PP
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.RS 4
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.EX
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$ factor 360
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360: 2 2 2 3 3 5
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.EE
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.RE
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.PP
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Factor the numbers on a line of standard input:
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.PP
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.RS 4
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.EX
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$ echo 91 1001 | factor
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91: 7 13
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1001: 7 11 13
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.EE
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.RE
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.PP
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List the primes up to 30, the numbers whose line has a single factor:
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.PP
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.RS 4
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.EX
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$ seq 2 30 | factor | awk \(aqNF == 2 { print $2 }\(aq
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.EE
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.RE
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.PP
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Print the largest prime factor of a number:
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.PP
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.RS 4
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.EX
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$ factor 600851475143 | awk \(aq{ print $NF }\(aq
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6857
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.EE
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.RE
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.SH NOTES
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Differences from GNU factor:
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.IP \(bu 2
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Numbers are limited to 64 bits.
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.IP \(bu 2
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There are no options other than
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.BR \-\-help ,
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so no
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.BR \-h ,
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.BR \-\-exponents ,
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or
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.BR \-\-version .
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.IP \(bu 2
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An invalid number ends the program, where GNU factor reports it and
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goes on to the next.
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.PP
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Factoring is by trial division.
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The slowest numbers, such as a prime near 2^64 or the product of two
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different primes near 2^32, take seconds.
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.PP
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Output lines end with LF, not CRLF.
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On standard input, a CR before the LF is removed, and a CR elsewhere is
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white space.
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.PP
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Write errors other than a closed pipe are ignored, and so is any error
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when the output buffer is flushed at exit: a short result written to a
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pipe whose reader has exited is lost, with status 0.
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.SH SEE ALSO
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.BR awk (1),
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.BR busybox (1),
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.BR seq (1)
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