File - Archive

The Archive task is able to compress and extract files with the formats Zip, Tar and GZip.

The different formats provides different functionality and compatibility across different operating systems. The Tar and GZip formats can be used to read or write archives between Windows and Linux/Unix. The Zip format is the most versatile and the most common in Windows workstations. It allows you to encrypt your archive with a password and select a compression level.

VisualCron's Tar implementation is fully compatible (reading and creating) with the "USTAR" (Unix Standard TAR) archive format. The implementation is capable of reading, but not writing files with a "posix Tar" or "GNU Tar" format, as long as archive entries do not use the header extensions from either of these formats. If unsupported header extensions are encountered when reading a Tar archive, an exception will be thrown.

The USTAR format has a few limitations, two of which should be emphasized. It should be noted that these are limitations of the USTAR format and not of VisualCron's implementation.

First, the underlying representation (i.e., in the Tar format itself) of the name of an item in a Tar archive is represented by two fields, Name and Prefix (which corresponds roughly to the pathname). These fields are combined and exposed through the FullName property. The combined length of the file and path names cannot exceed 256 characters.

The second limitation is that the maximum size of file that can be archived is 8 GB. This does not mean that the maximum size of a Tar archive is 8 GB; a Tar archive can contain as many 8 GB items as is allowed by the file system of the operating system.

Although Tar and GZip are more commonly used on Unix or Linux platforms, incorporating Xceed's implementations of these file formats into your applications will ensure maximum compatibility with file types.

Tar and GZip are usually used together. Tar is an archive; it gathers a collection of files or folders into a single file, while preserving file system information (such as permissions, dates and the folder structure). However, Tar does not compress the files in any way. The GZip format on the other hand is typically used to compress single files (although it is possible for a GZip archive to contain multiple files, see Multi-file operations for details).

Using these two formats together, Tar to create an archive and then compressing it with GZip, can potentially attain greater compression ratios than using a compressing archiver such as ZIP. The ZIP format compresses the individual files and then archives them into a single .zip file. With a GZip Tar file, files are first archived into a .tar file and then the complete archive is compressed. The advantage is that the compression engine searches for similar patterns across the entire archive, rather than just within each individual file, thereby increasing the chances of finding the patterns for this kind of compression. Another advantage in using GZip is that it is currently not encumbered by patents. As a result, there are no additional licensing fees to worry about. When used together, the resulting files typically have a .tar.gz or .tgz extension.

When the Archive task is selected in the task window you are presented with a set of sub tabs within the Archive tab.

Archive settings sub tab

Controls the main settings including what archiving format you would like to use and the archiving action; if you want to compress to an archive or extract an archive.

Archive action

An archive can either be compressed (assembled into one file), or extracted (unpacked to a folder structure). Compress and Extract has some special settings, which can be set in the tabs right to the Archive settings.

Archive type

VisualCron supports the archive types Zip, Tar and Tar+GZip.

Credential

An archiving activity involving another computer may require a network credential. Network credentials are globally managed in VisualCron and can be accessed from different parts in the application. Typically, click on the Manage credentials button to add a new credential.

Archive path

The archive path is the full path where your archive should be stored to or extracted from. You can choose any name for your archive but the following names are recommended:

Use password

Password protection and encryption is only selectable for the Zip format. When checking this box you first enter a password and then examine the settings in the Compress tab. The zip format supports a light encryption algorithm which uses a string password to encrypt it's data. This type of encryption can resist attacks by amateurs if the password is well chosen and long enough (at least 16 characters, maximum of 80) but it will probably not resist attacks by determined users or experts. Therefore you should use long passwords, and whenever possible, do not solely rely on this encryption system to protect sensitive data.

Compress sub tab

In this tab you select the special settings for an archive compression including compression level, method and strength.

Compression level

This option is available when the archive type Zip is selected. Set the compression level; higher compression level is slower but makes the file smaller.

Encryption method

This option is available when the archive type Zip is selected and password is used. There are two types of encryption methods available:

Compatible - The traditional ZIP encryption. This is a weak encryption method.

WinZipAES - The WinZip AES encryption method. This is a strong encryption method.

Encryption strength

This option is available when the archive type Zip is selected, password is used and WinZipAES encryption method is selected. Select an integer value representing the encryption strength of this file in bits, 256 is the highest bit setting and security of encryption strength.

Overwrite to archive if existing

When this option is selected, the archive will be overwritten (if existing).

Append to archive

If the archive exists it will be appended with new items.

Content sub tab

This sub tab contains a list of items/objects to be compressed. Click on Add to add a a new item.

When the Archive -> Content -> Add button is pressed, the Add/Edit archive item window is opened.

Source folder

Specify the full path to the folder you want to archive from.

File mask

The file mask provides a way to filter files that you want to include in the copying. The following wildcard characters are permitted in the File mask entry:

Characters other than the wildcard characters represent themselves. For example, the file mask string "*t" searches for all files names in the current path ending with the character "t". The search pattern string "s*" searches for all names starting with the character "s".

When the file extension is exactly three characters long, the File mask matching procedure differs from when the extension is more than three characters long. Using a File mask of exactly three characters returns files with file extensions of three or more characters. A File mask of one, two or more than three characters returns only files having file extensions of exactly the File mask length.

The following examples show the behavior of different lengths for the File mask parameter:

Of course, one specific file name may be entered as file mask.

Include sub folders

When this setting is checked and one or more files are matched, the corresponding source sub folder will be created in the archive.

Overwrite if existing

When this setting is checked, all matching files in the archive will be replaced if existing.

Append to archive

When this setting is checked only files that do not exist in the archive will be added.

The Extract sub tab This tab contains the extract path and some extra settings related to the extraction.

Note: When you are accessing a network drive (a folder on a remote computer) as source or destination folder you must specify the path in UNC format and not the letter of the logical drive. For example Y:\remotefolder\ must be specified as \\remoteservername\remotefolder\.