Page 50
do. But what if you want to do something and can't remember which program does what? In this case, you can turn to the apropos command.
For example, if you can't remember which command searches for files, you can enter
# apropos search apropos (1) - search the whatis database for strings badblocks (8) - search a device for bad blocks bsearch (3) - binary search of a sorted array. conflict (8) - search for alias/password conflicts find (1) - search for files in a directory hierarchy hcreate, hdestroy, hsearch (3) - hash table management lfind, lsearch (3) - linear search of an array. lkbib (1) - search bibliographic databases lookbib (1) - search bibliographic databases lsearch (n) - See if a list contains a particular element manpath (1) - determine user's search path for man pages strpbrk (3) - search a string for any of a set of characters strspn, strcspn (3) - search a string for a set of characters tsearch, tfind, tdelete, twalk (3) - manage a binary tree whatis (1) - search the whatis database for complete words. zgrep (1) - search possibly compressed files for a regular expression zipgrep (1) - search possibly zip files for a regular expression
You'll see a list of programs from the whatis database on your screen. The apropos command uses this database to search for the keyword you entered. If you keep your manual pages and whatis database up-to-date, you'll be able to use apropos to help you find the program you need.
| JUST A MINUTE |
You can also use the man command's -K option to do the same thing as apropos, but the search will be slow, and you'll be presented each manual page in the search result. For example, to search for any programs dealing with PostScript, you can try# man -K PostScriptThis can result in the following output (before you quit with q): |
Page 51
Now that you know about directory navigation, searching for files, or how to find more information about programs, I'll introduce you to other basic Linux commands you can use. This section shows you how to list the contents of directories, make a catalog of your hard drive, and read the contents of files. You'll learn the basic forms of these commands to help get you started.
The ls (list directory) command will quickly become one of your most often used programs. In its simplest form, ls lists nearly all of the files in the current directory. But this command, which has such a short name, probably has more command-line options (more than 75 at last count) than any other program!
In the simple form, ls lists your files:
# ls News axhome nsmail search author.msg documents reading vultures.msg auto mail research
You can also list the files as a single line, with comma separations, with the -m option:
# ls -m News, author.msg, auto, axhome, documents, mail, nsmail, reading, Â research, search, vultures.msg
If you don't like this type of listing, you can have your files sorted horizontally, instead of vertically (the default), with the -x option:
# ls -x News axhome nsmail search author.msg documents reading vultures.msg auto mail research
But are all these just files, or are there several directories? One way to find out is to use the -F option:
# ls -F News/ axhome/ nsmail/ search* author.msg documents/ reading/ vultures.msg auto/ mail/ research/
As you can see, the -F option causes the ls command to show the directories, each with a / character appended to the filename. The asterisk (*) shows that the file search is an executable program. But are these all the files in this directory? If you want to see everything, you can use the -a option with -F, as follows:
# ls -aF ./ .dt/ .neditdb auto/ ../ .dtprofile* .netscape/ axhome/
Page 52
.Xauthority .festival_history .newsrc documents/ .Xdefaults .forward .oldnewsrc mail/ .addressbook .fvwm2rc95* .pinerc nsmail/ .addressbook.lu .index/ .procmail/ reading/ .bash_history .mailcap .procmailrc research/ .bash_logout .mailrc .tin/ search* .bash_profile .mime.types .xinitrc* vultures.msg .bashrc .ncftp/ News/ .desksetdefaults .nedit author.msg
Using the -F option is one way to see the files and directories in your listings, but if you have a color monitor, or use X11 in color, you can tell ls to show files, directories, or executable files in different colors. To do this, use the --color option. In X11, using the rxvt terminal, directories will be blue, programs will be green, and regular files will be black. You can also customize which colors are used for different types of files.
Look in the /etc/ directory for the file named DIR_COLORS. Copy this file, renaming it to .dir_colors, and save it in your home directory. You can then edit this file to customize or add file types recognized for colorizing. See the DIR_COLORS file for details.
Long Directory Listing
Would you like even more information about your files? You can view the long format listing by using the ls -l option, for example:
# ls -l drwxr-xr-x 2 bball bball 1024 Nov 12 08:20 News -rw-rw-r-- 1 bball bball 4766 Nov 12 07:41 author.msg drwxrwxr-x 2 bball bball 1024 Nov 5 10:04 auto drwxrwxr-x 3 bball bball 1024 Nov 12 13:54 axhome drwxrwxr-x 2 bball bball 1024 Nov 12 14:33 documents drwx------ 2 bball bball 1024 Nov 12 14:02 mail drwx------ 2 bball bball 1024 Sep 15 01:57 nsmail drwxrwxr-x 2 bball bball 1024 Oct 29 20:28 reading drwxrwxr-x 5 bball bball 1024 Nov 5 10:03 research -rwxrwxr-x 1 bball bball 200 Oct 24 13:24 search -rw-rw-r-- 1 bball bball 801 Nov 11 22:46 vultures.msg
As you can see, there are eight different columns. The first column is the file's permissions flags, which are covered in Hour 21, "Handling Files." These flags generally show the file's type, and who can read, write (or modify or delete), or run the file. The next column shows the number of links, which are discussed in Hour 5, "Manipulation and Searching Commands." Next is the owner name, followed by group name. Owners and groups are discussed in Hour 21. The file size is listed next, followed by a timestamp of the file or directory was created or last modified. The last column, obviously, is each file's name.