156 lines
4.8 KiB
Groff
156 lines
4.8 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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.\"
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.TH DJ 1 2024-06-29 "Harakit X.X.X"
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.SH NAME
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dj \(en disk jockey
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.\"
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.SH SYNOPSIS
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dj
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.RB [ -Hn ]
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.RB [ -a\ byte ]
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.RB [ -c\ count ]
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.RB [ -i\ file ]
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.RB [ -b\ block_size ]
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.RB [ -s\ offset ]
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.RB [ -o\ file ]
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.RB [ -B\ block_size ]
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.RB [ -S\ offset ]
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.\"
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.SH DESCRIPTION
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Perform precise read and write operations on files. This utility is useful for
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reading and writing binary data to and from disks.
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This manual page uses the terms \(lqskip\(rq and \(lqseek\(rq to refer to moving
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to a specified byte by index in the input and output of the program
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respectively. This language is inherited from the
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.BR dd (1p)
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utility and used here to decrease ambiguity.
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When seeking or skipping to a byte, writing or reading starts at the byte
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immediately subsequent to the specified byte. Seeks and skips aren\(cqt counted
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in the output statistics because they're guaranteed to succeed (or the utility
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will exit unsuccessfully).
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.\"
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.SH OPTIONS
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.IP \fB-i\fP\ \fIfile\fP
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Takes a file path as an argument and opens it for use as an input.
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.IP \fB-b\fP\ \fIblock_size\fP
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Takes a numeric argument as the size in bytes of the input buffer, the default
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being 1024.
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.IP \fB-s\fP
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Takes a numeric argument as the index of the byte at which reading will
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commence; \(lqskips\(rq that number of bytes. If the standard input is used,
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bytes read to this point are discarded.
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.IP \fB-o\fP
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Takes a file path as an argument and opens it for use as an output.
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.IP \fB-B\fP\ \fIblock_size\fP
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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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.IP \fB-S\fP
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Takes a numeric argument as the index of the byte at which writing will
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commence; \(lqseeks\(rq that number of bytes. If the standard output is used,
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null characters are printed.
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.IP \fB-a\fP
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Accepts a single literal byte with which the input buffer is padded in the event
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of an incomplete read from the input file. If the option argument is empty, the
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null byte is used.
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.IP \fB-c\fP
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Specifies a number of reads to make. The default is 0, in which case the
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input is read until a partial or empty read is made.
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.IP \fB-H\fP
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Prints diagnostic messages in a human-readable manner as described in the
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DIAGNOSTICS section.
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.IP \fB-n\fP
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Retries failed reads once before exiting.
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.\"
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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 or if
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input file is \(lq-\(rq.
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.\"
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.SH STANDARD OUTPUT
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The standard output shall be used as an output if no inputs are specified or if
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the output file is \(lq-\(rq.
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.\"
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.SH DIAGNOSTICS
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On a partial or empty read, a diagnostic message is printed. Then, the program
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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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{records read} {ASCII unit separator} {partial records read}
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{ASCII record separator} {records written} {ASCII unit separator}
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{partial records written} {ASCII group separator} {bytes read}
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{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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{records read} '+' {partial records read} '>' {records written}
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'+' {partial records written} ';' {bytes read} '>' {bytes written}
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{ASCII line feed}
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.RE
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In non-recoverable errors that don\(cqt 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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.BR sysexits.h (3)
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status.
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.\"
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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 the
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.B -c
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option and a count, actual byte output is the product of the count and the input
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block size and therefore may be lower than expected. If the
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.B -a
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option is specified, this could make written data nonsensical.
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.\"
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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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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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.\"
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.SH RATIONALE
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This program was based on the
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.BR dd (1p)
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utility as specified in POSIX. While character conversion may have been the
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original intent of
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.BR dd (1p),
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it is irrelevant to its modern use. Because of this, this program eschews
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character conversion and adds typical option formatting, allowing seeks to be
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specified in bytes rather than in blocks, allowing arbitrary bytes as padding,
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and printing in a format that\(cqs easy for machines to parse.
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.\"
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.SH COPYRIGHT
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Copyright \(co 2023 DTB. License AGPLv3+: GNU AGPL version 3 or later
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<https://gnu.org/licenses/agpl.html>.
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.\"
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.SH SEE ALSO
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.BR dd (1p)
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