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| ls | list directory contents |
| cd | change working directory |
| pwd | print working directory |
| mkdir | create directory |
| rmdir | remove directory |
| cp | copy files |
| mv | move files |
| rm | delete files |
| more | view file contents |
| chmod | change file access permissions |
| man | view manual pages |
| ls Testdir1 | list the contents of the sub-directory Testdir1 |
| ls . | list the contents of the current directory |
| ls | list the contents of the current directory |
| ls .. | list contents of the parent of the current directory |
| ls ~ | list contents of home directory |
| ls /etc | list contents of the directory /etc (absolute pathname specified) |
| ls ~houdini | list contents of user houdini's home directory. |
ls can list the contents of multiple directories, if used in
the more general form:
ls <dir_name1> <dir_name2> <dir_name3> ...
In this form, ls prints the name of each directory, followed by the contents of the directory.
-a
Normally, ls does not list files or directories whose names
start with a . (dot). The -a option causes all files and directories to
be listed.
-l
The -l option lists the contents of a directory in the long
format. Given below is an example of the output produced by ls with
the
-l option.
% ls -l /class/cis221 drwxrwxr-x 6 weide cis22X-di 1024 Jan 23 1997 96au drwxrwxr-x 3 long cisfact 1024 Mar 4 14:05 97sp drwxrwxr-x 5 weide cisfact 1024 Jan 24 1997 97wi -rwxr-x--x 1 pillai cisgrad 129004 Nov 19 1996 Life.demo -rw-rw-r-- 1 pillai cisgrad 76 Nov 19 1996 Life1.dataThe output is organized into columns. The columns are (in the order in which they appear) - the file access permissions, number of links to the file, owner of the file, group for the file, file size, time of last modification and the name of the file.
The first field or column contains the file access permissions. The first character of this field is usually a "-" or a "d". A "d" means that the item is a directory; "-" means the item is a regular file. The interpretation of the remaining characters in this column depends, to some extent, on whether the item is a file or directory. The next nine characters indicate the access permissions. Of these, the first 3 denote the permissions for the owner of the file, the next 3 denote the permissions for the group members and the last 3 denote the permissions for everyone else.
"r" denotes read permission, "w" denotes write permission and "x" denotes execute permission. Read permission allows users to view the contents of a file and to copy it. Write permission allows users to modify the file. Execute permission allows users to run the file if it is executable.
In the sample output above, the owner of the file Life.demo has "r", "w" and "x" permissions, group members have "r" and "x" permissions but no "w" permission and others have only "x" permission. For the file Life1.data, the owner and group members have "r" and "w" permissions, while others have only "r" permission.
In the case of directories, permissions are interpreted in a slightly different way. Read permission allows users to list the contents of the directory. Write permission allows users to create files and sub-directories within the directory and execute permission allows users to search the directory. You will be able to access a file or directory using a pathname only if you have search permission on all intermediate directories in the path.
Access permissions can be changed by the owner using the chmod command.
cd <directory_name>
| cd Testdir1 | change to the sub-directory Testdir1 |
| cd .. | change to the parent of the current directory |
| cd ~ | change to the user's home directory |
| cd | change to the user's home directory |
| cd /etc | change to the directory /etc (absolute pathname specified) |
| cd ~houdini | change to the user houdini's home directory. |
Example: mkdir Testdir1 creates a new directory called Testdir1 as a subdirectory in the current working directory.
The directory being deleted must be empty.
Example: rmdir Testdir1 deletes the subdirectory Testdir1.
cp <src_file> <dest_file>
where <src_file> is the file to be copied and <dest_file> is the name of the copy being produced. Both <src_file> and <dest_file> can be pathnames. If <dest_file> exists, its contents are overwritten by the contents of <src_file>. If <dest_file> does not exist, it is created. <src_file> is not changed.
Example: cp /etc/motd motd_mycopy, creates a copy of the file /etc/motd in the current directory. The copy has the filename motd_mycopy.
Another common form of the cp command is:
cp <src_file> <dest_dir>
where <src_file> is as before and <dest_dir> is the directory into which it will be copied. If a file by the same name exists in <dest_dir>, its contents are overwritten. Otherwise, a new file with the same name as the source is created.
Example: cp /etc/motd ., creates a copy of the file /etc/motd in the current directory. The copy has the same name as the original i.e. motd.
cp can also be used to copy multiple files into a directory. For instance:
cp <src_file1> <src_file2> <src_file3> <dest_dir>
In this case, each of the source files is copied into the destination directory. This form of the command can be used to copy all files in one directory into another directory. For example:
Example: cp ~houdini/* ~, copies each file in user houdini's home directory into the current user's home directory. The copied files retain their names.
Another example: cp lab1.cpp lab2.cpp .., copies the files lab1.cpp and lab2.cpp in the current directory to the parent of the current directory.
The common forms of usage are:
mv <src_file> <dest_file>
mv <src_file> <dest_dir>
mv <src_file1> <src_file2> <src_file3> <dest_dir>
mv is frequently used to rename files. For example: mv motd motd_new renames the file motd in the current directory to motd_new.
Actually, the source does not have to be a file; mv can also move directories. Thus the following are correct forms of usage:
mv <src_dir> <dest_dir>
mv <src_dir1> <src_file2> <src_dir3> <dest_dir>
Example: mv Testdir1 .., moves the directory Testdir1 from the current directory to the parent of the current directory.
Example: rm lab1.cpp deletes the file lab1.cpp.
It's worth noting that more does not allow the user to go backwards in the file. For this reason, many users prefer the command less instead. It behaves similarly to more, but allows the user to scroll back up through data that have already been seen. The added functionality of less is classic evidence for the belief that "less is more" :-)
chmod <who>=<mode> <file>
where <who> denotes which class of permissions is being set, <mode> is the new set of permissions, and <file> is the name of the file or directory for which the permissions are being set.
<who> can be any combination of "u", "g" or "o" representing user (owner), group and other, respectively.
<mode> can be any combination of "r", "w" and "x" representing read, write and execute permissions, respectively.
For example: chmod g=rx lab1.cpp, sets the access permissions
for the group members for file lab1.cpp to read and execute, but
not write.
| chmod u=rwx lab1.cpp | for file lab1.cpp, set owner's access permissions to read, write and execute |
| chmod ug=rw lab1.cpp | owner and group members are given read and write permissions |
| chmod o=rx lab1.cpp | read and execute permissions for others |
The following two commands are equivalent:
chmod ugo=rw lab1.cpp
chmod a=rw lab1.cpp
In other words, if the desired access modes (permissions) for user, group and other are the same, you can use "a" (for all) instead of "ugo".
Permissions can be added using the chmod command as shown below:
chmod <who>+<mode> <file>
Existing permissions can be removed using the form of the chmod
command shown below:
chmod <who>-<mode> <file>
| chmod ug+x lab1.cpp | for file lab1.cpp, add execute permission to the set of permissions for the owner and group |
| chmod o-w lab1.cpp | remove write from the set of permissions for others |
Example: man mkdir lists the manual page for the command mkdir.
This form of the command is useful when the user already knows the command that is needed but wants to get more detailed information on the usage of the command.
man uses more to display the manual page.
Example: man -k directories will result in man printing out a list of commands that deal with directory manipulations.
With the -k option, man lists all commands that are related to the specified keyword and a one line description of each command.
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