Compression

Author: cirosantilli

7zip.md

@@ -0,0 +1,13 @@
+# 7zip
+
+Microsoft proprietary program.
+
+Can do lots of formats:
+
+- 7z format
+- RAR with `p7zip-rar` installed
+- zip
+
+But *use only for 7z*, which it was made for.
+
+With 7zip, you can open `.exe` files to extract their inner data.

README.md

@@ -118,7 +118,6 @@ Media video, games, etc.) file types, viewers, editors, capture, synthesizers:
 
 - [Audio](audio/): audio, music, sound.
 - [Book](book.md): PDF, DJVU.
-- [Compression](compression.md): Zip, tar, gzip, 7z.
 - [Dictionary](dictionary.md): dictionary formats.
 - [Game](game.md): games, emulation.
 - [Image](image/): images, photos.
@@ -133,6 +132,15 @@ File sharing:
 - [NFS](nfs.md) (WIP)
 - [LDAP](ldap.md) (WIP)
 
+[Compression](compression.md):
+
+- [7zip](7zip.md)
+- [File Roller](file-roller.md)
+- [RAR](rar.md)
+- [gzip](gzip.md)
+- [tar](tar.md)
+- [zip](zip.md)
+
 User operations:
 
 - [id](id.md)

compression.md

@@ -1,8 +1,6 @@
 # Compression
 
-File compression formats and utilities.
-
-The performance parameters are:
+The main performance parameters to consider when choosing the compression method are:
 
 - compression ratio
 - compression time
@@ -11,263 +9,7 @@ The performance parameters are:
 - ability to break into chunks
 - keep file metadata such as permissions, hidden (windows), etc.
 
-## ZIP
-
-Most widely supported format.
-
-Not so high compression rate.
-
-Easy to view and extract single files.
-
-Compresses dir file by file it seems.
-
-ZIP file or directory:
-
-    zip -r "$F".zip "$F"
-
-`-r`: add dir recursively. Otherwise, adds only the top dir and not its contents.
-
-Using it on a directory will keep the top directory in the ZIP. To avoid that and keep only the files in the directory, do:
-
-    cd dir
-    zip -r ../dir.zip .
-
-If you don't have hidden files on the top level:
-
-    zip -r dir.zip dir/*
-
-Note that:
-
-    zip -r dir.zip dir/.*
-
-will not work by default for hidden files, since `.*` will also expand to `.` and `..` with default `bash` options.
-
-`-e`: encrypt:
-
-    zip -er "$F".zip "$F"
-
-You can still see filenames, but not extract them!
-
-List all files in zip file
-
-    unzip -l "$F".zip
-
-Extract files from zip:
-
-    unzip "$F".zip
-
-If has password, asks for it.
-
-To a dir:
-
-    unzip "$F".zip -d out
-
-    for F in *; do echo "$F"; echo "$F".zip; zip "$F".zip "$F"; done
-
-ZIP every file in cur dir to file.zip
-
-## tb2
-
-## tgz
-
-## tar
-
-Name origin: `Tape ARchive`.
-
-The tar *format* is specified by POSIX 7 together with the `pax` utility: <http://pubs.opengroup.org/onlinepubs/9699919799/utilities/pax.html#tag_20_92>
-
-The `tar` is a GNU implementation, and is not specified by POSIX.
-
-tar only turns a dir into file, but does no compression.
-
-It is a popular option to transform directories in to files in Nix systems, as the format natively stores and preserves ext filesystem metadata such as:
-
-- ownership
-- permissions
-- symlinks
-- timestamps
-
-Since tar offers no compression, it is often coupled with `gz` and `bz2`: those are files compressors.
-
-tar end compressions are used so commonly together that shorthand extensions exist for them:
-
-- `tgz` == `tar.gz`
-- `txz` == `tar.xz`
-- `tb2` == `tbz` == `tar.bz2`
-
-General GNU interface:
-
-- single char options don't start with hyphen
-- every single letter option has a corresponding double hyphen multi char version
-
-Create tar:
-
-    tar vcf "$F".tar "$F"
-    tar vczf "$F".tgz "$F"
-    tar vcjf "$F".tbz "$F"
-    tar vcJf "$F".txz "$F"
-
-- `c`: create
-- `f`: set output file to next argument. If not given, outputs to stdout.
-- `z`: `gzip`
-- `j`: `bzip2`
-- `v`: verbose
-
-If the output file exists, it is overwritten.
-
-Create from tar with multiple files:
-
-    tar vcf a.tar f1 f2
-
-`r`: append file to existing tar, or create new tar:
-
-    tar rcf a.tar f
-
-Extract:
-
-    tar vxf "$F".tar
-    tar vxzf "$F".tgz
-    tar vxjf "$F".tbz
-
-## zlib
-
-## gzip
-
-## gunzip
-
-## gz
-
-Extension: `gz`.
-
-Library name: zlib, GNU.
-
-Popular wrapper: `gzip`, and `gunzip` to unzip.
-
-Vs zip:
-
--   Completely different file types.
-
--   Both use the DEFLATE algorithm: <https://en.wikipedia.org/wiki/DEFLATE>, and therefore have very similar compression ratios and speeds.
-
--   The zlib library does not focus on directories: only single files. For this reason it is commonly used together with `tar` which only packs directories into a file. For convenience however, the command line executable can deal with `.tgz` files.
-
--   gzip seems to have very one dominant implementation: GNU zlib, so that gzip can refer to either the utility or format used by that utility.
-
-    zip has many implementations: WinRAR, WinZip on closed source on Windows, Info-ZIP and libzip open source, Info-ZIP being the default one present on Ubuntu 12.04. Therefore the term zip usually only refers to the file format.
-
-If a file is only `.gz` but not `.tgz` you cannot use tar to extract it.
-
-Create `a.txt.gz` and `rm` `a.txt`:
-
-    gzip a.txt
-
-Extract `a.gz` and erase it if successful:
-
-    gunzip a.gz
-
-`.gz` all files under given directory recursively individually. Remove each original:
-
-    gzip -r .
-
-### gz file format
-
-IETF standardized format: <https://www.ietf.org/rfc/rfc1952.txt>
-
-### Hardlinks
-
-### Keep original
-
-Does not work if the file has any hard links, probably because that would not reduce memory usage as it breaks the hardlink. AKA: tries to be too smart and annoys us to hell!
-
-Workaround: keep the original on the operations: <http://unix.stackexchange.com/questions/46786/how-to-tell-gzip-to-keep-original-file>
-
-Workarounds: `-c` outputs to stdout:
-
-    gzip -c a > a.gz
-
-Read input from stdin:
-
-    gzip < a > a.gz
-
-And finally, `gzip` 1.6 (2013) has the `-k, --keep` option:
-
-    gzip -k a
-    gzip -kr .
-
-## RAR
-
-Proprietary `Roshal ARchive`, after it's creator Eugene Roshal.
-
-Can do split archive.
-
-Split archive extensions match the following Perl regexes:
-
-- `.part\d+\.rar`
-- `.r\d+`
-
-Extract contents of `a.rar` to `./`
-
-    unrar x a.rar
-
-Before / after:
-
-    a.rar
-    /dir1/
-    /dir1/f1
-    /dir1/f2
-
-    ===============
-
-    a.rar
-    dir1/f1
-    dir1/f2
-
-Out to `./out/` directory, creates this directory if necessary:
-
-    unrar x a.rar out
-
-Extract multipart RAR:
-
-    unrar x a.r00
-    unrar x a.part1.rar
-
-Recursively find all files in `a.rar`, and outputs them to current dir with old basename possible name conflicts:
-
-    unrar e a.rar
-
-Sample output:
-
-    a.rar
-    /dir1/
-    /dir1/f1
-    /dir1/f2
-
-    ===============
-
-    a.rar
-    f1
-    f2
-
-### Create RAR
-
-`a` for add:
-
-    rar a dir.rar dir
-
-## 7zip
-
-Microsoft proprietary program.
-
-Can do lots of formats:
-
-- 7z format
-- RAR with `p7zip-rar` installed
-- zip
-
-But *use only for 7z*, which it was made for.
-
-With 7zip, you can open `.exe` files to extract their inner data.
-
-## File roller
+If you don't have very strict constraints, default to:
 
-Very good GUI app to view inside multiple archive formats and extract them.
+- `zip` if you want OS portability
+- `tar.gz` if you want to maintain Linux filesystem metadata intact: permissions, symlinks, etc.

file-roller.md

@@ -0,0 +1,3 @@
+# File Roller
+
+Very good GUI app to view inside multiple archive formats and extract them.

gzip.md

@@ -0,0 +1,43 @@
+# gzip
+
+# zlib
+
+# gunzip
+
+# gz
+
+Extension: `gz`.
+
+Library name: zlib, GNU.
+
+Popular wrapper: `gzip`, and `gunzip` to unzip.
+
+Vs zip:
+
+-   Completely different file types.
+
+-   Both use the DEFLATE algorithm: <https://en.wikipedia.org/wiki/DEFLATE>, and therefore have very similar compression ratios and speeds.
+
+-   The zlib library does not focus on directories: only single files. For this reason it is commonly used together with `tar` which only packs directories into a file. For convenience however, the command line executable can deal with `.tgz` files.
+
+-   gzip seems to have very one dominant implementation: GNU zlib, so that gzip can refer to either the utility or format used by that utility.
+
+    zip has many implementations: WinRAR, WinZip on closed source on Windows, Info-ZIP and libzip open source, Info-ZIP being the default one present on Ubuntu 12.04. Therefore the term zip usually only refers to the file format.
+
+If a file is only `.gz` but not `.tgz` you cannot use tar to extract it.
+
+Create `a.txt.gz` and `rm` `a.txt`:
+
+    gzip a.txt
+
+Extract `a.gz` and erase it if successful:
+
+    gunzip a.gz
+
+`.gz` all files under given directory recursively individually. Remove each original:
+
+    gzip -r .
+
+### gz file format
+
+IETF standardized format: <https://www.ietf.org/rfc/rfc1952.txt>