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COMPRESSION UTILITIES

Windows compression utilities

  • Windows XP Compressed Folders: Windows XP includes an embedded compression utility. A compressed folder can be opened and navigated like any other folder in the system. You may "copy" the files or use the "Extract" option under the File menu. To create a compressed folder, select "File > New > Compressed Folder".

  • WinZIP: This is a Windows based shareware (try-before-you-pay) program. Using WinZip, a document written by Kellogg Information Systems, includes installation instructions and examples of how to create a ZIP archive and how to expand an existing ZIP archive. The advantage of WinZIP over the embedded feature in Windows XP is that WinZIP will recognize additional compression formats.

Compression in Unix

There are several commands available in Unix systems to compress files and expand compressed files. Please check the manual pages (man command) for each command for more information.

  • zip, unzip: These are the equivalents of the DOS unzip or WinZip utilities.

  • compress, uncompress: The "compress" command creates files with extension "Z" (the capital is important). UNIX will compress the file and delete the original. "uncompress" will do the opposite: restore the original file and delete the compressed version. "Compress" and "uncompress" work when writing and reading from a disk.

  • zcat: "zcat" reads a file created with "compress" and sends the content to standard output (the screen). This is a useful feature to access the data in a compressed file without expanding it. Statistical packages such as SAS can take advantage of this command using a Unix "pipe". For example, SAS users could include a FILENAME statement like the one below:

    filename mydata pipe 'gzcat ~netid/data.Z';
    Stata users can accomplish something similar by writing a shell script. Refer to the Stata FAQ "How do I read data from a pipe?".

  • gzip, gunzip, and gzcat: GNU zip utility. GNU is a project of the Free Software Foundation" (it stands for "GNU’s Not UNIX"). GNU’s web site is www.gnu.org. gzip compresses "gzcat" works like "zcat" for files with the "gz" extension.

  • pack, unpack: A less used group of commands, they compress files, adding the ".z" extension.

Note: Files with extension "tar" were created with the UNIX "tar" command (Tape ARchive). These are not compressed files, just files grouped in an archive, a collection of files. Most frequently you will see them "g-zipped" as well: "filename.tar.gz". WinZip can uncompress and "restore" these files, reproducing directory structure.

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