% go_tutorialthis will create a directory called tutorial in your home directory.
When you log into the system you are place in your home directory. In the following examples we will assume that the home directory is /home/huron2/admin/scot
% pwd /home/huron2/admin/scot %If you are using the using a shell that allows you to set the prompt you can change the prompt to be the current location in the directory structure.
% cd /usr/bin % pwd /usr/bin %
When we changed to the /usr/bin directory we specified its full pathname, since it starts from the root. If we were located in the /usr directory and we wanted to change to /usr/bin we could use cd bin instead of specify the path from the top of the filesystem, this is known as the relative pathname since it is relative to your current directory.
There are special characters that are used as directory abbreviations. If we were in the /home/huron2/admin/scot directory and we wanted to go to the parent directory or /home/huron2/admin we would use the comand cd .. to change to the parent directory.
If you know the username of another user you can change to their directory without specifying the full pathname. The T-shell will recognize the ~username to mean the home directory for that particular user. The ~ by itself refers to your home directory.
Table4.2: T-Shell Directory Abbreviations ----------------------------------------------------------------------------- . Current directory .. Next directory "up" in the hierarchy. Also called parent directory ~ Your home directory ~username The usernames's home directory -----------------------------------------------------------------------------If you want to return to your home directory from any location in the directory hierarchy type in cd with no options.
% cd % pwd /home/huron2/admin/scot %Change to the tutorial directory, if you are following interactively.
% cd tutorial %
% ls Makefile friends friends.pl hello.cc postscript %
Files starting with a . (dot) are hidden files. This means that ls won't normally display them. To display these files we must use the -a (all) option. Generally files are hidden because they are system files, there is no reason to display them under most circumstances. Most system dot files reside in your home directory.
When we do an ls it is difficult to tell which files are directories and which are plain files. The -F (full) option to ls will append a slash (/) to files that are directories, a asterisk(*) to executable files, and an at sign(@) to hard links .
% ls -F Makefile friends friends.pl* hello.cc postscript/ %This tells us that we have one executable and one directories in the current directory.
One of the most common ways to list the files in a directory is with the -l (long) option.
% ls -l total 10 -rw-r--r-- 1 scot admin 242 Mar 7 17:00 Makefile -rw-r--r-- 1 scot admin 416 Mar 23 12:20 friends -rwxr--r-- 1 scot admin 868 Mar 15 14:24 friends.pl -rw-r--r-- 1 scot admin 70 Mar 7 17:00 hello.cc drwxr-xr-x 2 scot admin 1024 Mar 24 15:43 postscript %The -l option gives information on the file permissions, number of hard links , file owner, file group, file size, time last modified and the file name.
An argument to ls is the file or directory you want to list, if no argument is given ls lists the current directory. However, if you use ls with the directory name as the argument you will get a listing of the files and directories located in that directory. If you wanted to see the permission of the directory use the -d (directory) option.
% ls -l postscript total 656 -rw-r--r-- 1 scot admin 326291 Mar 18 13:02 mosaic.ps % ls -ld postscript/ drwxr-xr-x 2 scot admin 1024 Mar 24 16:17 postscript/ %
The chmod command uses the plus(+) sign to add permissions and a minus(-) sign to remove permissions. Therefore the final syntax is the user class(u, g, or o) followed by the action to take(+ or -), followed by the permission to change(r,w, or x).
% ls -l friends -rw-r--r-- 1 scot admin 416 Mar 23 12:20 friends % chmod g+w friends % ls -l friends -rw-rw-r-- 1 scot admin 416 Mar 23 12:20 friends %To change the permissions of all classes of users we could do the following.
% chmod ugo+x friends % ls -l friends -rwxrwxr-x 1 scot admin 416 Mar 23 12:20 friends %Instead of specifying the three groups we can use the a(all) option, for all users.
% chmod a-x friends % ls -l friends -rw-rw-r-- 1 scot admin 416 Mar 23 12:20 friends %
When you first create a file it is given a set of permissions, that are determined by the umask (user mask) which is a built-in shell command.
% umask 22 %The umask command without any arguments will display the current values. Actually the umask is 022 but leading zeros are ignored. The number is called a mask because each digit is subtracted from a system default value. The default value is usually rw-rw-rw- or 666 in octal notation. Because the umask is subtracted from the default value you cannot turn on permissions that are already turned off in the default value. Use the chmod command to turn on permissions.
Table4.4: Determining the umask ----------------------------------------------------------------- Octal Value Corresponding permissions ----------------------------------------------------------------- 666 (current default permissions) rw-rw-rw- -600 (permissions you want) rw------- ---- 066 (umask) ----------------------------------------------------------------The T-shell uses a default umask of 022 which will create files with rw-r--r-- permissions. The only arguments to umask is to set the umask.
% umask 066 % touch new % ls -l new -rw------- 1 scot admin 0 Mar 29 09:51 new %
The touch command will create a new file if no arguments are given or update the modification time of a file that has already been created. With a umask of 066 only the creator of the file will be able to read or write to the file, therefore you might want to change the umask back to 022.
% umask 022The chmod command supports the -R (recursive) option to change the permissions in a directory and all its sub-directories.
% cp friends friends.copy % ls f* friends friends.copy friends.pl %The -r (recursive) allows you to copy whole directories, including subdirectories.
% cp -r postscript post % ls -d p* post postscript %
% mv friends.copy friends.old % ls f* friends friends.old friends.pl %The mv command can also be used to rename or move entire directories.
% mv post posters % ls -d p* posters postscript %
The mkdir (make directory) command is used to create one or more new directories.
% mkdir temp % ls -ld temp drwx--x--x 2 scot admin 24 Apr 4 13:23 temp %
% rm friends.old % ls f* friends friends.pl %If you use the -i (interactive) option, rm checks with you before removing each file that you specify. Sometimes files are write protected. If you try to remove these files the rm command prompts you on whether to remove a write protected file. The -f (force) option forces the removal of files even if they are write protected.
The -r (recursive) option in used to remove entire directories and all sub-directories below thedirectory.
% rm -r posters %Another command to remove directories is the rmdir (remove directory) command. Unlike the rm -r command the rmdir command requires that the directory be empty.
There are two types of links hard links and symbolic links or soft links. Hard links cannot point to directories or to files in a different file system, whereas symbolic links can. If you use the ln command with no options you will get a hard link. The -s (symbolic) option is used to get a symbolic link. The format of the ln command is:
ln [options] existing_file link_name
Lets create a symbolic link to the temp directory.
% ln -s temp temp2 % ls -ld t* drwxr-xr-x 2 scot admin 24 Mar 25 12:07 temp lrwxr-xr-x 1 scot admin 4 Mar 25 13:11 temp2 -> temp %A symbolic link to a directory is not a directory, so to remove it you don't need the -r(recursive) option.
% rm temp2 % ls -ld t* drwxr-xr-x 2 scot admin 24 Mar 25 12:07 temp %A common symbolic link for programmers is to have a link named core that points to /dev/null. Core files are generated when a program "core dumps" or produces debugging output. These core files take a tremendous amount of storage, and are used infrequently. The /dev/null is the Unix equivalent of a trash can. In effect, what you are doing is telling the system to toss this file away whenever it is created.
% ln -s /dev/null core % ls -l c* lrwxr-xr-x 1 scot admin 9 Mar 25 13:34 core -> /dev/null %Caveat: with symbolic links you can remove the "real" file and the symbolic link will still exist.
Lets get specific information about the mosaic.ps file, that is located in our postscript directory
% file postscript/mosaic.ps mosaic.ps: postscript file -version 2.0 %Now we know that the file is an postscript file.