8. The Remaining 1%

8.1 Using tar & gzip

Under UNIX there are some widely used applications to archive and compress files. tar is used to make archives---it's like PKZIP but it doesn't compress, it only archives. To make a new archive:

$ tar -cvf <archive_name.tar> <file> [file...]

To extract files from an archive:

$ tar -xpvf <archive_name.tar> [file...]

To list the contents of an archive:

$ tar -tf <archive_name.tar> | less

You can compress files using compress, which is obsolete and shouldn't be used any more, or gzip:

$ compress <file>
$ gzip <file>

that creates a compressed file with extension .Z (compress) or .gz (gzip). These programs can compress only one file at a time. To decompress, use:

$ compress -d <file.Z>
$ gzip -d <file.gz>

RMP.

The unarj, zip and unzip (PK??ZIP compatible) utilities are also available. Files with extension .tar.gz or .tgz (archived with tar, then compressed with gzip) are as common in the UNIX world as .ZIP files are under DOS. Here's how to list the contents of a .tar.gz archive:

$ gzip -dc <file.tar.gz> | tar tf - | less

or, equivalently,

$ tar -ztf <file.tar.gz> | less

8.2 Installing Applications

First of all: installing packages is root's work. Some Linux applications are distributed as .tar.gz or .tgz archives, specifically prepared so that they can be decompressed from / typing the following command:

# gzip -dc <file.tar.gz> | tar xvf -

or, equivalently,

$ tar -zxf <file.tar.gz>

The files will be decompressed in the right directory, which will be created on the fly. Users of the Slackware distribution have a user-friendly pkgtool program; another is rpm, which is available on all distributions thanks to Red Hat.

Most programs shouldn't be installed from /; typically, the archive will contain a directory called pkgname/ and a lot of files and/or subdirectories under pkgname/. A good rule is to install those packages from /usr/local. Besides, some programs are distributed as C or C++ source files, which you'll have to compile to create the binaries. In most cases, all you have to do is issue make. Obviously, you'll need the gcc or g++ compiler.

8.3 Tips You Can't Do Without

Command completion: pressing <TAB> when issuing a command will complete the command line for you. Example: you have to type gcc this_is_a_long_name.c; typing gcc thi<TAB> will suffice. (If you have other files that start with the same characters, supply enough characters to resolve any ambiguity.)

Backscrolling: pressing SHIFT + PAG UP (the grey key) allows you to backscroll a few pages, depending on how much video memory you have.

Resetting the screen: if you happen to more or cat a binary file, your screen may end up full of garbage. To fix things, blind type reset or this sequence of characters: echo CTRL-V ESC c RETURN.

Pasting text: in console, see below; in X, click and drag to select the text in an xterm window, then click the middle button (or the two buttons together if you have a two-button mouse) to paste. There is also xclipboard (alas, only for text); don't get confused by its very slow response.

Using the mouse: install gpm, a mouse driver for the console. Click and drag to select text, then right click to paste the selected text. It works across different VCs.

Messages from the kernel: have a look at /var/adm/messages or /var/log/messages as root to see what the kernel has to tell you, including bootup messages. The command dmesg is also handy.

8.4 Useful Programs and Commands

This list reflects my personal preferences and needs, of course. First of all, where to find them. Since you all know how to surf the Net and how to use archie and ftp, I'll just give you three of the most important addresses for Linux: ftp://sunsite.unc.edu, ftp://tsx-11.mit.edu, and ftp://nic.funet.fi. Please use your nearest mirror.

• at allows you to run programs at a specified time;
• awk is a simple yet powerful language to manipulate data files (and not only). For example, being data.dat your multi field data file,

  $ awk '$2 ~ "abc" {print $1, "\t", $4}' data.dat
  

  prints out fields 1 and 4 of every line in data.dat whose second field contains ``abc''.
• cron is useful to perform tasks periodically, at specified date and time;
• delete-undelete do what their name means;
• df gives you info about all mounted disk(s);
• dosemu allows you to run several (not all) DOS programs---including Windows 3.x, with a bit of hacking;
• file <filename> tells you what filename is (ASCII text, executable, archive, etc.);
• find (see also Section dir) is one of the most powerful and useful commands. It's used to find files that match several characteristics and perform actions on them. General use of find is:

  $ find <directory> <expression>
  

  where <expression> includes search criteria and actions. Examples:

  $ find . -type l -exec ls -l {} \;
  

  finds all the files that are symbolic links and shows what they point to.

  $ find / -name "*.old" -ok rm {} \;
  

  finds all the files matching the pattern and deletes them, asking for your permission first.

  $ find . -perm +111
  

  finds all the files whose permissions match 111 (executable).

  $ find . -user root
  

  finds all the files that belong to root. Lots of possibilities here---RMP.
• gnuplot is a brilliant program for scientific plotting;
• grep finds text patterns in files. For example,

  $ grep -l "geology" *.tex
  

  lists the files *.tex that contain the word ``geology''. The variant zgrep works on gzipped files. RMP;
• tcx compresses executable binaries keeping them executable;
• joe is an excellent editor. Invoking it by typing jstar you'll get the same key bindings as WordStar and its offspring, including DOS and Borland's Turbo languages editors;
• less is probably the best text browser, and if properly configured lets you browse gzipped, tarred, and zipped files as well;
• lpr <file> prints a file in background. To check the status of the printing queue, use lpq; to remove a file from the printing queue, use lprm;
• mc is a great file manager;
• pine is a nice e-mailing program;
• script <script_file> copies to script_file what appears on screen until you issue the command exit. Useful for debugging;
• sudo allows users to perform some of root's tasks (e.g. formatting and mounting disks; RMP);
• uname -a gives you info about your system;
• zcat and zless are useful for viewing gzipped text files without ungzipping them. Possible use:

  $ zless textfile.gz
  $ zcat textfile.gz | lpr
  

• The following commands often come in handy: bc, cal, chsh, cmp, cut, fmt, head, hexdump, nl, passwd, printf, sort, split, strings, tac, tail, tee, touch, uniq, w, wall, wc, whereis, write, xargs, znew. RMP.

8.5 Common Extensions and Related Programs

You may come across scores of file extensions. Excluding the more exotic ones (i.e. fonts, etc.), here's a list of who's what:

• 1 ... 8: man pages. Get man.
• arj: archive made with arj. unarj to unpack.
• dvi: output file produced by TeX (see below). xdvi to visualise it; dvips to turn it into a PostScript .ps file.
• gif: graphic file. Get seejpeg or xpaint.
• gz: archive made with gzip.
• info: info file (sort of alternative to man pages). Get info.
• jpg, jpeg: graphic file. Get seejpeg.
• lsm: Linux Software Map file. It's a plain ASCII file containing the description of a package.
• ps: PostScript file. To visualise or print it get gs and, optionally, ghostview.
• rpm: Red Hat package. You can install it on any system using the package manager rpm.
• tgz, tar.gz: archive made with tar and compressed with gzip.
• tex: text file to submit to TeX, a powerful typesetting program. Get the package tex, available in many distributions; but beware of NTeX, which has corrupted fonts and is included in some Slackware versions.
• texi: texinfo file, can produce both TeX and info files (cp. info). Get texinfo.
• xbm, xpm, xwd: graphic file. Get xpaint.
• Z: archive made with compress.
• zip: archive made with zip. Get zip and unzip.