This chapter is from the book
This chapter is from the book
This chapter is from the book
Working with Files
Managing files in your home directory involves using one or more easily remembered commands.
Creating a File with touch
To create an empty file called filename within your current directory, use the following command:
matthew@seymour:~$ touchfilename
To edit this file, you must use a text editor. Several are discussed in Chapter 12, “Automating Tasks and Shell Scripting.” However, it is sometimes useful to create an empty file as this creates an access record because of the time and date information that is connected to the file. You can also use touch to update this information, called a timestamp, without otherwise accessing or modifying a file.
You can create a file in a different location by changing what is after touch. To create a new file in /home/matthew/randomdirectory, if I am already in my home directory, I can use the following:
matthew@seymour:~$ touch randomdirectory/newfile
Or from anywhere using an absolute path, I use this:
matthew@seymour:~$ touch /home/matthew/randomdirectory/newfile
Or from anywhere using a path shortcut, I use the following command:
matthew@seymour:~$ touch ~/randomdirectory/newfile
Creating a Directory with mkdir
To create an empty directory called newdirectory within your current directory, use this command:
matthew@seymour:~$ mkdir newdirectory
You can create a directory in a different location by changing what is after mkdir. To create a new directory in /home/matthew/music, if I am already in my /home directory, I can use the following:
matthew@seymour:~$ mkdir music/newdirectory
Or from anywhere using an absolute path, I can use this:
matthew@seymour:~$ mkdir /home/matthew/music/newdirectory
Or from anywhere using a path shortcut, I can use the following command:
matthew@seymour:~$ mkdir ~/music/newdirectory
The -p option is valuable. It enables you to create a directory and its parent directories at the same time, if they do not already exist. This can be a real time saver. If the parent directories exist, the command works normally. For example, suppose I want to make a new directory with two layers of subdirectories. In this example, music and newdirectory already exist, but subdir1 and subdir2 are to be created:
matthew@seymour:~$ mkdir -p ~/music/newdirectory/subdir1/subdir2
Deleting a Directory with rmdir
To delete an empty directory named directoryname, use the following command:
matthew@seymour:~$ rmdir directoryname
You can remove a directory in a different location by changing what is after rmdir. To remove a directory in /home/matthew/music, if I am already in my /home directory, I can use the following:
matthew@seymour:~$ rmdir music/directoryname
Or from anywhere using an absolute path, I can use this:
matthew@seymour:~$ rmdir /home/matthew/music/directoryname
Or from anywhere using a path shortcut, I can use the following command:
matthew@seymour:~$ rmdir ~/music/directoryname
The directory must be empty to be removed using rmdir. However, there is a way to remove a directory with its contents using rm.
Deleting a File or Directory with rm
To delete a file named filename, use this command:
matthew@seymour:~$ rm filename
You can remove a directory in a different location by changing what is after rm. To remove a directory in /home/matthew/randomdirectory, if I am already in my /home directory, I can use the following:
matthew@seymour:~$ rm randomdirectory/filename
Or from anywhere using an absolute path, I can use this:
matthew@seymour:~$ rm /home/matthew/randomdirectory/filename
Or from anywhere using a path shortcut, I can use the following command:
matthew@seymour:~$ rm ~/randomdirectory/filename
If you try to use rm to remove an empty directory, you will receive an error message: rm: cannot remove `random/': Is a directory. In this case, you must use rmdir. However, you can remove a directory and its contents using rm.
To delete a directory and all its contents, use the -R recursive switch. This switch works with many commands, not only rm:
matthew@seymour:~$ rm -R /home/matthew/randomdirectory/
Everything in randomdirectory as well as in the directory itself will be deleted.
Moving or Renaming a File with mv
In Linux land, moving and renaming a file are the same thing. It doesn’t matter whether you are moving the directory to another or from one filename to another filename in the same directory, there is only one command to remember. To move a file named filename from ~/documents to ~/archive, use this command:
matthew@seymour:~$ mv documents/filename archive
Notice that the filename is not included in the destination. The destination here must be an existing directory. If it is not, the file is renamed to the term used. Some examples will make this clear.
To rename a file that is in my current directory, I could use the following:
matthew@seymour:~$ mv oldfilename newfilename
To rename a file as I move it from ~/documents to ~/archive, I could use this:
matthew@seymour:~$ mv documents/oldfilename archive/newfilename
Or from anywhere using an absolute path, I could use the following command:
matthew@seymour:~$ mv /home/matthew/documents/oldfilename/home/matthew/archive/newfilename
Or from anywhere using a path shortcut, I could use this:
matthew@seymour:~$ rm ~/documents/oldfilename ~/archive/newfilename
Copying a File with cp
Copying works similarly to moving, but retains the original in the original location. To copy a file named filename from ~/documents to ~/archive, use this command:
matthew@seymour:~$ cp documents/filename archive
Notice that the filename is not included in the destination. The destination here must be an existing directory. If it is not, the file is renamed to the term used. Some examples will make this clear.
To copy a file that is in my current directory I could use the following, and it will work exactly the same as mv, except that both files will exist afterward:
matthew@seymour:~$ cp oldfilename newfilename
To rename a file as I copy it from ~/documents to ~/archive, I could use this:
matthew@seymour:~$ cp documents/oldfilename archive/newfilename
Or from anywhere using an absolute path, I could use the following command:
matthew@seymour:~$ cp /home/matthew/documents/oldfilename/home/matthew/archive/newfilename
Or from anywhere using a path shortcut, I can use this:
matthew@seymour:~$ cp ~/documents/oldfilename ~/archive/newfilename
Displaying the Contents of a File with cat
To view the contents of a text file named filename on your screen, use this command:
matthew@seymour:~$ cat filename
Notice that the text is displayed on your screen but that you cannot edit or work with the text in any way. This command is convenient when you want to know the contents of a file but don’t need to make any changes. Text editors for the terminal are covered in Chapter 10, “Command-Line Master Class.” This command works best with short files because the contents of longer files will scroll off of the screen too quickly to be read.
Displaying the Contents of a File with less
When you need to view the contents of a longer text file from the command line, you can use less. This produces a paged output, meaning that output stops each time your screen is full. You can then use your up- and down-arrow keys and page-up and page-down keys to scroll through the contents of the file. Then, use q to quit and return to the command line:
matthew@seymour:~$ less filename
There was a program that did give paged output in the early days of UNIX called more. It was the first paged output program but did not include the ability to scroll up and down. less was written to add that capability and was named as a bit of hacker humor because “ less is more.” You can also use more, but today it is merely an alias for less.
Using Wildcards and Regular Expressions
Each of these commands can be used with pattern-matching strings known as wildcards or regular expressions. For example, to delete all files in the current directory beginning with the letters abc, you can use an expression beginning with the first three letters of the desired filenames. An asterisk (*) is then appended to match all these files. Use a command line with the rm command like this:
matthew@seymour:~$ rm abc*
Linux shells recognize many types of file naming wildcards, but this is different from the capabilities of Linux commands supporting the use of more complex expressions. You learn more about using wildcards in Chapter 10, “Command-Line Master Class,” and in Chapter 12, “Automating Tasks and Shell Scripting.”