The DP4 tar Utility

A version of the Unix tar (tape archive) program is available from Itim Technology Solutions. tar saves and restores a collection of files into a single .tar file, which can then be transferred easily to another machine via the FTP utility. This is much more convenient that transferring many files individually.

Tar Utility Syntax

The syntax of the tar utility is:

where key is one of:

-c Create a new archive file and add the named files to it

-x Extract the named files from the archive file. If no filenames are specified, every file is extracted

-t List the names of files in the archive

Additional arguments may be supplied:

-f filename Take filename as the name of the archive file.

-v Verbose. For -c or -x print each filename as it is processed. For -t provide a full directory listing

-w Print each filename to be processed and wait for user input; the action will be skipped unless it is confirmed by pressing the letter 'y' (yes)

-m Do not restore the file modification times; the modification time of each file is the time at which it is extracted from the tape or disk

-D Perform automatic conversion to, and from, MS-DOS format. This option can be specified multiple times. Specifying it a second time turns automatic conversion off for subsequent files, specifying it a third time tuens automatic conversion back on again, and so on.

-Z Perform automatic compression or uncompression: see below

-F <filename> Process the list of files named in <filename> . This argument may be repeated as often as required

Creating an Archive File

Arguments to the tar utility can be combined in any reasonable way, for example:

and

are equivalent. Both of these command lines create a new archive file, containing the files listed in listfile. While the archive is being created, the names of files are displayed as they are processed. The archive file is a raw disk file and can be used to transfer files to Unix machines.

Some points worth noting are:

• If you include more arguments after listfile, they are taken as the names of files to process
• Wildcards can be used and are expanded according to the usual MS-DOS/Windows conventions
• Any filename prefixed with '@' is treated as the name of a file containing a list of further arguments, in similar way to the -F option. The previous example could also be entered as: tar -cvf file.tar @listfile

Source and Target File Renaming

An argument of the form:

causes automatic renaming. With the -c option, the MS-DOS file 'sourcename' is stored in the archive under the name ' targetname . For example, the command: tar -cvf file.tar /opt/dp4/dbs/system.dat=c:\dp4\db\system.dat

could be used to prepare a disk on an MS-DOS machine for transfer to a Unix system. The command:

could be used to recover the file back onto an MS-DOS machine.

File Conversion Options

If the -D option is supplied:

• Files copied to archives have CR/LF converted to LF
• Files copied from archive have LF converted to CR/LF

If the -Z option is supplied:

• Files copied to tape are automatically compressed and the suffix .Z added to their name (if it is not already present)
• Files copied from tape will be uncompressed if they appear to be compressed and any suffix .Z removed from their name. The algorithm used is compatible with the Unix compress, uncompress and zcat utilities.

Work Files

In operation, tar may create temporary files with the names tar.tmp and tar.$$$ .

Tar Utility Restrictions

Be aware of the restrictions that the DP4 tar utility imposes when investigating its compatibilities with your Unix tarcommand:

• The -r (append to end of tape) and -u (update tape) options are not supported
• Genuine magnetic tape is not supported
• Wildcard file names are expanded according to the MS-DOS convention; directory names are not followed recursively as occurs in the Unix version
• Linked files are ignored
• Permissions are ignored when restoring on MS-DOS/Windows
• Files are stored with permission rw-rw-rw- or rwxrwxrwx and user and group id both set to 100. You can use -X to toggle x permission on and off.
• In the UK the environment variable TZ must be set to GMT0BST in the winter or GMT1BST in the summer; otherwise the modification times on the tape correspond to the wrong time zone. In other countries set the TZ variable according to the number of hours you are in front of or behind Univeral Time (Greenwich Mean Time)
• When extracting a tar file prepared on a Unix/Linux machine no attempt is made to deal with Unix filenames which are not valid filenames on MS-DOS Windows (e.g. con).
• The -D and -Z options cannot be combined.

• The -D option will destroy any non-text file.