Hidden Files

Hidden Files

An invisible file is one whose first character is the dot or period character (.). UNIX programs (including the shell) use most of these files to store configuration information.

Some common examples of hidden files include the files −

• .profile − the Bourne shell ( sh) initialization script
• .kshrc − the Korn shell ( ksh) initialization script
• .cshrc − the C shell ( csh) initialization script
• .rhosts − the remote shell configuration file

To list invisible files, specify the -a option to ls −

$ ls -a

.         .profile       docs     lib     test_results
..        .rhosts        hosts    pub     users
.emacs    bin            hw1      res.01  work
.exrc     ch07           hw2      res.02
.kshrc    ch07.bak       hw3      res.03
$

• Single dot . − This represents current directory.
• Double dot .. − This represents parent directory.

Creating Files

You can use vi editor to create ordinary files on any Unix system. You simply need to give following command −

$ vi filename

Above command would open a file with the given filename. You would need to press key i to come into edit mode. Once you are in edit mode you can start writing your content in the file as below −

This is unix file....I created it for the first time.....
I'm going to save this content in this file.

Once you are done, do the following steps −

• Press key esc to come out of edit mode.
• Press two keys Shift + ZZ together to come out of the file completely.

Now you would have a file created with filemame in the current directory.

$ vi filename
$

Editing Files

You can edit an existing file using vi editor. We would cover this in detail in a separate tutorial. But in short, you can open existing file as follows −

$ vi filename

Once file is opened, you can come in edit mode by pressing key i and then you can edit file as you like. If you want to move here and there inside a file then first you need to come out of edit mode by pressing key esc and then you can use following keys to move inside a file −

• l key to move to the right side.
• h key to move to the left side.
• k key to move up side in the file.
• j key to move down side in the file.

So using above keys you can position your cursor where ever you want to edit. Once you are positioned then you can use i key to come in edit mode. Edit the file, once you are done press esc and finally two keys Shift + ZZ together to come out of the file completely.

Display Content of a File

You can use cat command to see the content of a file. Following is the simple example to see the content of above created file −

$ cat filename
This is unix file....I created it for the first time.....
I'm going to save this content in this file.
$

You can display line numbers by using -b option along with cat command as follows −

$ cat -b filename
1   This is unix file....I created it for the first time.....
2   I'm going to save this content in this file.
$

Counting Words in a File

You can use the wc command to get a count of the total number of lines, words, and characters contained in a file. Following is the simple example to see the information about above created file −

$ wc filename
2  19 103 filename
$

Here is the detail of all the four columns −

• First Column: represents total number of lines in the file.
• Second Column: represents total number of words in the file.
• Third Column: represents total number of bytes in the file. This is actual size of the file.
• Fourth Column: represents file name.

You can give multiple files at a time to get the information about those file. Here is simple syntax −

$ wc filename1 filename2 filename3

Copying Files:

To make a copy of a file use the cp command. The basic syntax of the command is −

$ cp source_file destination_file

Following is the example to create a copy of existing file filename.

$ cp filename copyfile
$

Now you would find one more file copyfile in your current directory. This file would be exactly same as original file filename.

Renaming Files

To change the name of a file use the mv command. Its basic syntax is −

$ mv old_file new_file

Following is the example which would rename existing file filename tonewfile:

$ mv filename newfile
$

The mv command would move existing file completely into new file. So in this case you would fine only newfile in your current directory.

Deleting Files

To delete an existing file use the rm command. Its basic syntax is −

$ rm filename

Caution: It may be dangerous to delete a file because it may contain useful information. So be careful while using this command. It is recommended to use-i option along with rm command.

Following is the example which would completely remove existing filefilename:

$ rm filename
$

You can remove multiple files at a tile as follows −

$ rm filename1 filename2 filename3
$