218 lines
4.9 KiB
Groff
218 lines
4.9 KiB
Groff
.\" Copyright (c) 2024 DTB <trinity@trinity.moe>
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.\" Copyright (c) 2024 Emma Tebibyte <emma@tebibyte.media>
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.\"
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.\" This work is licensed under CC BY-SA 4.0. To see a copy of this license,
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.\" visit <http://creativecommons.org/licenses/by-sa/4.0/>.
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.TH dj 1
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.SH NAME
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dj \(en disk jockey
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.SH SYNOPSIS
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dj
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.RB ( -AdHnq )
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.RB ( -a
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.RB [ byte ])
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.RB ( -c
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.RB [ count ])
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.RB ( -i
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.R [
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.B input file
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.R ])
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.RB ( -b
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.R [
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.B input block size
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.R ])
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.RB ( -s
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.R [
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.B input offset
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.R ])
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.RB ( -o
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.R [
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.B output file
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.R ])
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.RB ( -B
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.R [
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.B output block size
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.R ])
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.RB ( -S
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.R [
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.B output offset
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.R ])
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.SH OPTIONS
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.B -i
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.RS
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Takes a file path as an argument to open and use as an input.
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.RE
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.B -b
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.RS
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Takes a numeric argument as the size in bytes of the input buffer, with the
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default being 1024.
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.RE
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.B -s
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.RS
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Takes a numeric argument as the number of bytes to skip into the input
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before starting to read. If the standard input is used, bytes read to this point
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are discarded.
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.RE
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.B -o
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.RS
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Takes a file path as an argument to open and use as an output.
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.RE
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.B -B
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.RS
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Does the same as
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.B -b
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but for the output buffer.
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.RE
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.B -S
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.RS
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Skips a number of bytes through the output before starting to write from
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the input. If the output is a stream, null characters are printed.
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.RE
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.B -a
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.RS
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Accepts a single literal byte with which input buffer is padded in the event
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of an incomplete read from the input file.
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.RE
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.B -c
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.RS
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Specifies a number of reads to make. If set to zero (the default), reading will
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continue until a partial or empty read is encountered.
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.RE
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.B -A
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.RS
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Specifying this option pads the input buffer with null bytes in the event of an
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incomplete read. Equivalent to specifying
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.B -a
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with a null byte instead of a character.
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.RE
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.B -d
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.RS
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Prints invocation information before program execution as described in the
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DIAGNOSTICS section below. Each invocation increments the debug level of the
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program.
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.RE
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.B -H
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.RS
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Prints diagnostics messages in a human-readable manner as described in the
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DIAGNOSTICS section below.
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.RE
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.B -n
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.RS
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Retries failed reads once more before exiting.
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.RE
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.B -q
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.RS
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Suppresses error messages which print when a read or write is partial or
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empty. Each invocation decrements the debug level of the program.
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.RE
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.SH STANDARD INPUT
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The standard input shall be used as an input if no inputs are specified one or
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more of the input files is “-”.
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.SH DIAGNOSTICS
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On a partial or empty read, a diagnostic message is printed (unless the
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.B -q
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option is specified) and the program exits (unless the
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.B -n
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option is specified.
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By default statistics are printed for input and output to the standard error in
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the following format:
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.RS
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.R {records read} {ASCII unit separator} {partial records read}
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.R {ASCII record separator} {records written} {ASCII unit separator}
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.R {partial records written} {ASCII group separator} {bytes read}
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.R {ASCII record separator} {bytes written} {ASCII file separator}
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.RE
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This format for diagnostic output is designed to be machine-parseable for
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convenience. For a more human-readable format, the
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.B -H
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option may be specified. In this event, the following format is used instead:
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.RS
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.R {records read} '+' {partial records read} '>' {records written}
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.R '+' {partial records written} ';' {bytes read} '>' {bytes written}
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.R {ASCII line feed}
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.RE
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If the
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.B -d
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option is specified, debug output will be printed at the beginning of execution.
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This debug information contains information regarding how the program was
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invoked. The following example is the result of running the program with
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.B -d
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as the only argument:
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.RS
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.R argv0=dj
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.R in=<stdin> ibs=1024 skip=0 align=ff count=0
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.R out=<stdout> obs=1024 seek=0 debug= 3 noerror=0
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.RE
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In non-recoverable errors that don’t pertain to the read-write cycle, a
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diagnostic message is printed and the program exits with the appropriate
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sysexits.h(3) status.
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.SH BUGS
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If
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.B -n
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is specified along with a specified count, actual byte output may be lower than
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expected (the product of the count multiplied by the input block size). If the
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.B -a
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or
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.B -A
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options are used this could make data written nonsensical.
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Many lowercase options have capitalized variants and vice-versa which can be
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confusing. Capitalized options tend to affect output or are more intense
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versions of lowercase options.
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.SH CAVEATS
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Existing files are not truncated on ouput and are instead overwritten.
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.SH RATIONALE
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This program was based on the dd(1p) utility as specified in POSIX. While
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character conversion may have been the original intent of dd(1p), it is
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irrelevant to its modern use. Because of this, it eschews character conversion
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and adds typical option formatting, allowing seeks to be specified in bytes
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rather than in blocks, allowing arbitrary bytes as padding, and printing in a
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format that’s easy to parse for machines.
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.SH COPYRIGHT
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Copyright © 2023 DTB. License AGPLv3+: GNU AGPL version 3 or later
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<https://gnu.org/licenses/agpl.html>.
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.SH SEE ALSO
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dd(1p)
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