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Split cat, tac, and others, index od and hd
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‎README.md

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@@ -4,7 +4,7 @@ Linux information and cheatsheets.
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Includes Linux concepts and utilities that work on Linux, not necessarily in the LSB.
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##Index
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## Index
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Important files:
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@@ -40,31 +40,15 @@ Base topics:
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- [Special files](special-files.md): `proc`, `dev` and `sys` filesystems.
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- [Terminal](terminal.md): terminal emulators, ANSI escapes, control characters.
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Media video, games, etc.) file types, viewers, editors, capture, synthesizers:
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Basic stream and file manipulation:
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- [Audio](audio/): audio, music, sound.
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- [Book](book.md): PDF, DJVU.
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- [Compression](compression.md): Zip, tar, gzip, 7z.
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- [Dictionary](dictionary.md): dictionary formats.
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- [Game](game.md): games, emulation.
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- [File sharing](files-sharing.md): Soulseek, Dropbox.
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- [Image](image/): images, photos.
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- [Markup](markup/): Markdown, RST. Focus on command line interface and extensions.
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- [Video](video.md): videos, films, subtitles.
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- [cat](cat.md)
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- [head](head.md)
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- [tac](tac.md)
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- [tail](tail.md)
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- [truncate](truncate.md)
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Generic data formats:
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- [JSON](json.md)
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- [Unicode](unicode.md)
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- [XML](xml/)
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Markup compilers:
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- [Kramdown](kramdown/)
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- [Pandoc](pandoc/)
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- [RST](rst/)
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File and directory related utilities:
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File and directory:
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- [du](du.md)
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- [fdupes](fdupes.md)
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- [ls](ls.md)
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- [tree](tree.md)
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Programming tools:
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Diff:
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- [comm](comm.md)
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- [cmp](cmp.md)
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Binary data viewers:
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- [hd](hd.md)
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- [hexdump](hexdump.md)
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- [od](od.md)
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Programming:
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- [ack](ack.sh)
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- [Compile](compile/): compilation process, dynamic libraries.
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Process-related tools:
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Processes:
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- [chroot](chroot.sh)
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- [env](env.sh)
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- [ulimit](ulimit.md)
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- [wait](wait.sh)
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Other tools:
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Media video, games, etc.) file types, viewers, editors, capture, synthesizers:
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- [Audio](audio/): audio, music, sound.
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- [Book](book.md): PDF, DJVU.
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- [Compression](compression.md): Zip, tar, gzip, 7z.
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- [Dictionary](dictionary.md): dictionary formats.
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- [Game](game.md): games, emulation.
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- [File sharing](files-sharing.md): Soulseek, Dropbox.
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- [Image](image/): images, photos.
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- [Markup](markup/): Markdown, RST. Focus on command line interface and extensions.
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- [Video](video.md): videos, films, subtitles.
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Generic data formats:
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- [JSON](json.md)
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- [Unicode](unicode.md)
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- [XML](xml/)
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Markup compilers:
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- [Kramdown](kramdown/)
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- [Pandoc](pandoc/)
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- [RST](rst/)
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Misc:
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- [eval](eval.sh)
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- [C++ Cheat](https://github.com/cirosantilli/cpp-cheat): contains some compilation / language heavy subjects like the POSIX C API or generation of dynamic libraries.
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- [Networking Cheat](https://github.com/cirosantilli/networking-tutorial): networking tools and protocols: HTTP, SSH, curl Apache.
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##How to search for keywords
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## How to search for keywords
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If you know what you are searching for, use the following methods to search by keyword.
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‎cat.md

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##cat
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POSIX 7: <http://pubs.opengroup.org/onlinepubs/9699919799/utilities/cat.html>
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Concatenate files to stdout.
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```sh
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echo asdf > a
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echo qwer > b
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[ "$(cat a)" = 'asdf' ] || exit 1
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[ "$(cat b)" = 'qwer' ] || exit 1
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[ "$(cat a b)" = "$(printf 'asdf\nqwer'") ] || exit 1
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```
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Stdin:
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```sh
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[ "$(echo a | cat)" = 'a' ] || exit 1
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```

‎cmp.md

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# cmp
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GNU Diffutils package.
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Compares F and G byte by byte, until first difference is found.
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cmp "$F" "$G"
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If equal, print nothing.
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Else, print location of first difference.
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## s
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Silent
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Return status `0` if equal, `1` otherwise.
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Prints nothing.
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cmp -s "$F" "$G"
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if [ $? -eq 1 ]; then
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echo neq
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else
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echo eq
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fi

‎comm.md

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# comm
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Ordered list diff.
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POSIX 7. <http://pubs.opengroup.org/onlinepubs/9699919799/utilities/comm.html>
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Coreutils package.
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cd "`mktemp -d`"
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echo -e "a\nc" > a
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echo -e "b\nc" > b
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comm a b
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Output:
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a
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\tb
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\t\tc
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This produces 3 columns by indentation:
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- lines only in `a`
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- lines only in `b`
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- lines in both

‎hd.md

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# hd
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`od` alternative with better defaults, but not POSIX 7.
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Uses saner hexadecimal defaults and shows ASCII side by side.
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Saner than hexdump.
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Very close to hexdump, but also shows ASCII visualization on the side of hexa visualization.
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Example:
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echo -en {a..z} "\n \x01" | hd
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Output:
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00000000 61 20 62 20 63 20 64 20 65 20 66 20 67 20 68 20 |a b c d e f g h |
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00000010 69 20 6a 20 6b 20 6c 20 6d 20 6e 20 6f 20 70 20 |i j k l m n o p |
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00000020 71 20 72 20 73 20 74 20 75 20 76 20 77 20 78 20 |q r s t u v w x |
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00000030 79 20 7a 20 0a 20 01 |y z . .|
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00000037
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Non ASCII and whitespace chars or control chars such as newline or `\x01` are represented as dots on the ASCII side notation.
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Offsets are in hexadecimal: 00, 10, 20.

‎head.md

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# head
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POSIX 7: <http://pubs.opengroup.org/onlinepubs/9699919799/utilities/head.html>
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Keep only 10 first lines:
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seq 20 | head
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Keep only 2 first lines:
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[ "$(printf '1\n2\n3\n4\n' | head -n2)" = "$(printf '1\n2\n')" ] || exit 1
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2 first bytes:
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[ "$(echo -en 'abc' | head -c 2)" = 'ab' ] || exit 1
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## GNU extensions
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Remove last two bytes:
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[ "$(echo -en 'abc' | head -c -2)" = 'a' ] || exit 1

‎hexdump.md

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# hexdump
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`od` alternative with better defaults, but not POSIX 7.
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Uses saner hexadecimal defaults.
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`hd` has even saner defaults.
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View bytes in hexadecimal.
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echo -n abc | hexdump -C
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Options:
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- `-C` : see bytes in hexadecimal
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- `-n32` : only 32 bytes
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- `-s32` : start at byte 32
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- `-v`: show duplicate lines
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- `-e '1/1 " %02X"'`: format string

‎od.md

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#od
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# od
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`od` and similar tools used to view binary data.
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View binary data.
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POSIX 7: <http://pubs.opengroup.org/onlinepubs/9699919799/utilities/od.html>
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Saner non-POSIX 7 alternatives: `hd`, `hexdump`.
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Very useful for viewing binary data which contains values which cannot be interpreted as some character set (ASCII, UTF-8) that can be printed to terminal screen.
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You have some fun exploring things such as:
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- executables such as elf files
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- executables such as elf files
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- partition tables:
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- partition tables:
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sudo hd -n 512 /dev/sda
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POSIX 7
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Octal dump.
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View byte values byte by byte in octal and other bases.
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Maximum number of bytes to read.
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#hd
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Very similar to od.
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Uses saner hexadecimal defaults and shows ASCII side by side.
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Not POSIX 7.
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Saner than hexdump.
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Very close to hexdump, but also shows ASCII visualization on the side of hexa visualization.
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Example:
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echo -en {a..z} "\n \x01" | hd
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Output:
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00000000 61 20 62 20 63 20 64 20 65 20 66 20 67 20 68 20 |a b c d e f g h |
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00000010 69 20 6a 20 6b 20 6c 20 6d 20 6e 20 6f 20 70 20 |i j k l m n o p |
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00000020 71 20 72 20 73 20 74 20 75 20 76 20 77 20 78 20 |q r s t u v w x |
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00000030 79 20 7a 20 0a 20 01 |y z . .|
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00000037
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Non ASCII and whitespace chars or control chars such as newline or `\x01` are represented as dots on the ASCII side notation.
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Offsets are in hexadecimal: 00, 10, 20.
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#hexdump
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Very similar to od, but not POSIX 7.
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Uses saner hexadecimal defaults.
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`hd` has even saner defaults.
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View bytes in hexadecimal.
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echo -n abc | hexdump -C
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Options:
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- `-C` : see bytes in hexadecimal
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- `-n32` : only 32 bytes
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- `-s32` : start at byte 32
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- `-v`: show duplicate lines
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- `-e '1/1 " %02X"'`: format string

‎sed.sh

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# TODO make all asserts pass
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# POSIX 7
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# POSIX 7 <http://pubs.opengroup.org/onlinepubs/9699919799/utilities/sed.html>
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# Stream EDitor
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‎tac.md

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# tac
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`cat` reversed line-wise.
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Coreutils.
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[ "$(printf "a\nb\n" | tac)" = "$(printf "b\na")" ] || exit 1
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Things get messy if the input does not end in newline:
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[ "$(printf "a\nb" | tac)" = "$(printf "ba")" ] || exit 1

‎tail.md

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# tail
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POSIX 7:
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Opposite of head.
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Show last 10 lines:
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seq 20 | tail
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Keep only 2 last lines:
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[ "$(printf "1\n2\n3\n4\n" | tail -n2)" = "$(printf "3\n4\n")" ] || exit 1
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## GNU Coreutils extensions
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Keep only lines from the Nth onwards:
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[ "$(printf "1\n2\n3\n4\n" | tail -n +2)" = "$(printf "2\n3\n4\n")" ] || exit 1
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[ "$(printf "1\n2\n3\n4\n" | tail -n +3)" = "$(printf "3\n4\n")" ] || exit 1

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