Decompressing and Decoding Files

Eventually you will come across files that have been compressed or encoded in some way. Compression, just as you might think, makes a file smaller so that it may be transmitted more quickly (there's less to transmit). Encoding changes the form of a file, usually so it can be transmitted as email.

Below are instructions on how to undo some of the more popular compression and encoding schemes. All of the commands below assume you're in your Unity account.

Files compressed with Stuffit (end with .sit) and CompactPro (end with .cpt) must be dealt with on a Macintosh or Intel-compatible machine; there are no tools to handle these on Unity.

You should be aware of three things:

1. Compressed and encoded files are usually identified by their extensions, the character code following the file name. Depending on how they were compressed, some files won't decompress or decode if the extension is removed. Here are some common extensions for compressed and encoded files:

   Compressed files

   • filename.Z (a compressed file)
   • filename.gz (a GNU compressed file)
   • filename.z (a GNU compressed file -- note lowercase 'z')
   • filename.zip (a zipped archive)
   • filename.tar (a tarred file)
   • filename.tar.Z (a file both tarred and compressed)
   • filename.tar.gz (a file both tarred and GNU compressed)
   • filename.tgz (abbreviated form of tarred and GNU compressed)
   • filename.bz (a file compressed with bzip)
   • filename.bz2 (a file compressed with bzip2)

   Encoded files

   • filename.uu (a uuencoded file)
   • filename.hqx (a binhexed file)


2. The names of compressed and encoded files may change when the files are decompressed or decoded. For example, the file "test.uu" could be called "first_test.txt" after it's decoded. Likewise, file.Z would become file. You may need to look carefully at your directory listing to find the new file.
3. Decompressing or decoding a file creates a new file or files, but it doesn't necessarily remove the original compressed or encoded file. You usually have to remove the original when you're finished with it.

Decompressing files with .Z endings

To decompress a file with the extension .Z (uppercase), enter the command

compress -d filename.Z

The decompressed file will appear in your directory listing, and the original .Z file will be removed.

Warning: If you run out of available disk space during the decompression, you'll lose both the decompressed file and the compressed file. The gunzip command below can "safely" decompress a .Z file.

Decompressing files with .gz or .z endings

For a file with the extension .gz or .z (lowercase 'z' only), decompress the file by using the command

gunzip filename.gz

The decompressed file will appear in your directory listing, and the original .gz or .z file will be removed.

Decompressing files with .bz or .bz2 endings

For a file with the extension .bz or .bz2, you must first gain access to the bzip and/or bzip2 commands by typing:

add zutils

Then, if the file ends in .bz, you uncompress it by using the command:

bzip -d filename.bz

or, if the file ends in .bz2, you uncompress it by using the command:

bzip2 -d filename.bz2

The decompressed file will appear in your directory listing, and the .bz or .bz2 will be removed.

Decompressing files with .zip endings

To unzip the file, use the command

unzip filename.zip

These .zip files tend to produce more than one file when uncompressed.

Decompressing files with .tar endings

A file with the .tar extension contains a number of other files and even directories compressed (tar-ed) together. TAR stands for "tape archive" and is used primarily with tape drives.

To decompress a .tar file, type

tar -xvf filename.tar

The decompressed file will appear in your directory listing, but the original .tar file will not be removed.

Because a .tar file may contain a large number of files and directories, it's usually a good idea to place it in its own directory before you decompress it. This keeps all the component files in one place and avoids confusion with other files.

To see what's inside a .tar file without decompressing it, enter

tar -tf filename.tar

Decompressing files with more than one extension

You may come across a file such as

filename.tar.Z

First you must use the decompression utility appropriate for the last extension. Then use the decompression utility for the first extension. For example, to decompress the file "filename.tar.Z", you must first use the command

compress -d filename.tar.Z

and then the command

tar -xvf filename.tar

Decoding

Decoding files with .uu endings

Binary files (graphics and programs) can't be sent through Unix email systems as binaries and must first be converted to text-based forms. This conversion, called "uuencoding," is not compression; in fact, uuencoded files actually get larger.

To decode a .uu file, enter

uudecode filename.uu

Note that because uuencoding is so common, many people don't even bother to include the ".uu" file extension. If you look at a file using the more command, and you see characters such as

begin 644 einstein.jpg M_]C_X``02D9)1@`!`0```0`!``#_VP!#``@&!@TG!0@'!P!)"0@*#!0-#`L+ M#!D2$P\4'1H?'AT:'!P@)"XG("(L(QP!*#!I+#`Q-#0T'R!Y/3@R/"XS-#+E

the file is a uuencoded binary file, and you should use the uudecode command to convert it to its binary form.

Converting files with .hqx endings to MacBinary format

Moving Macintosh files around the Internet requires that they be converted to a form called binhex that Unix machines can understand and transmit. As with uuencoded files, binhexed files actually get larger, but you'll be able to send them through email.

MacBinary is a special format used to store and transmit Macintosh files that are composed of many pieces. The resource fork of the Macbinary file holds the icon and file type information, and the data fork stores almost everything else. To gain access to the mcvert program that both unbinhexes a binhexed file and converts it to a MacBinary file, enter

add macutils

followed by the command

mcvert -x filename.hqx

Note: There is an Intel-based binhex format that performs the same function on Intel-compatible computers. Currently there are no programs in Unity that convert binhexed files to Intel-based binary format.

Content last updated May, 20004, by daniel
Page last modified October 19, 2005 by cawalker