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The UNIX file command allows you to determine whether an unknown file is in text format, suitable for direct viewing. |
EXERCISE: Type the command |
file /bin/sh |
to see what kind of file the shell is. |
EXPLANATION: The shell is a shared executable, indicating that the file contains binary instructions to be executed by the computer. |
The cat command |
The cat command concatenates files and sends them to the screen. You can specify one or more files as arguments. |
Cat makes no attempt to format the text in any way, and long output may scroll off the screen before you can read it. |
EXAMPLE: Send the contents of your .profile file to the screen by typing |
cat ~/.profile |
to the shell. The tilde character (~) is UNIX shorthand for your home directory. |
The more command |
The more command displays a text file, one screenful at a time. You can scroll forward a line at a time by pressing the return key, or a screenful at a time by pressing the spacebar. You can quit at any time by pressing the q key. |
EXAMPLE: Type |
more /etc/rc |
to the shell. Scroll down by pressing return, and by pressing the spacebar. Stop the more command from displaying the rest of the file by typing q. |
The head and tail commands |
The head command allows you to see the top part of a file. You may specify the number of lines you want, or default to ten lines. |
EXAMPLE: Type |
head -15 /etc/rc |
to see the first fifteen lines of the /etc/rc file. |
The tail command works like head, except that it shows the last lines of of file. |
EXAMPLE: Type |
tail /etc/rc |
to see the last ten lines of the file /etc/rc. Because we did not specify the number of lines as an option, the tail command defaulted to ten lines. |
Copying files and directories |
The UNIX command to copy a file or directory is cp. The basic cp command syntax is cp source destination. |
EXAMPLE: The command |
cp ~/.profile ~/pcopy |
makes a copy of your .profile file, and stores it in a file called "pcopy" in your home directory. |
EXERCISE: Describe the permissions necessary to successfully execute the command in the previous example. |
EXPLANATION: To copy the .profile file, one must have read permission on the file. To create the new file called pcopy, one must have write permission in the directory where the file will be created. |
Moving and renaming files |
The UNIX mv command moves files and directories. You can move a file to a different location in the filesystem, or change the name by moving the file within the current location. |
EXAMPLE: The command |
mv ~/pcopy ~/qcopy |
takes the pcopy file you created in the cp exercise, and renames it "qcopy". |
Removing files |
The rm command is used for removing files and directories. The syntax of the rm command is rm filename. You may include many filenames on the command line. |
EXAMPLE: Remove the the shrccopy file that you placed in your home directory in the section on moving files by typing |
rm ~/.shrccopy |
Creating a directory |
The UNIX mkdir command is used to make directories. The basic syntax is mkdir directoryname. If you do not specify the place where you want the directory created (by giving a path as part of the directory name), the shell assumes that you want the new directory placed within the current working directory. |
EXAMPLE: Create a directory called foo within your home directory by typing |
mkdir ~/foo |
EXERCISE: Create a directory called bar, within the directory called foo, within your home directory. |
EXPLANATION: Once the foo directory is created, you could just type |
mkdir ~/foo/bar |
Alternately, you could type |
cd ~/foo; mkdir bar |
In the second solution, two UNIX commands are given, separated by a semicolon. The first part of the command makes foo the current working directory. The second part of the command creates the bar directory in the current working directory. |
Removing a directory |
Subsets and Splits