1. Guide To UNIX Using Linux Third Edition
Chapter Four:
UNIX/Linux File Processing
Guide To UNIX Using Linux Third Edition

2. Objectives Explain UNIX and Linux file processing
Use basic file manipulation commands to create, delete, copy, and move files and directories
Employ commands to combine, cut, paste, rearrange, and sort information in files
Guide to UNIX Using Linux, Third Edition

3. Objectives (continued)
Create a script file
Use the join command to link files using a common field
Use the awk command to create a professional-looking report
Guide to UNIX Using Linux, Third Edition

4. UNIX and Linux File Processing
Based on the approach that files should be treated as nothing more than character sequences
Because you can directly access each character, you can perform a range of editing tasks – this offers flexibility in terms of file manipulation
Guide to UNIX Using Linux, Third Edition

5. Reviewing UNIX/Linux File Types
Regular files, also known as ordinary files
Create information that you maintain and manipulate, and include ASCII and binary files
Directories
System files for maintaining file system structure
Guide to UNIX Using Linux, Third Edition

6. Reviewing UNIX/Linux File Types (continued)
Special files
Character special files relate to serial I/O devices
Block special files relate to devices such as disks
Guide to UNIX Using Linux, Third Edition

7. Understanding File Structures
Files can be structured in many ways depending on the kind of data they store
UNIX/Linux store data, such as letters and product records, as flat ASCII files
Three kinds of regular files are
Unstructured ASCII character
Unstructured ASCII records
Unstructured ASCII trees
Guide to UNIX Using Linux, Third Edition

8. Understanding File Structures (continued)
Guide to UNIX Using Linux, Third Edition

9. Processing Files
UNIX/Linux processes commands by receiving input from a standard input device (e.g. keyboard) and sending it to a standard output device (e.g. monitor)
System administrators and programmers refer to standard input as stdin, standard output as stdout
When UNIX/Linux detect errors, they send data to standard error (stderr, the monitor)
Guide to UNIX Using Linux, Third Edition

10. Using Input and Error Redirection
You can use redirection operators to retrieve input from something other than the standard input device and send output to something other than the standard output device
Examples of redirection
Redirect the ls command output to a file, instead of to the monitor (or screen)
Redirect a program that receives input from the keyboard to receive input from a file instead
Redirect error messages to files, instead of to the screen by default
Guide to UNIX Using Linux, Third Edition

11. Manipulating Files
When you manipulate files, you work with the files themselves, as well as their contents
Create files using output redirection
cat command - concatenate text via output redirection
without a command - > filename
touch command - creates empty files
Guide to UNIX Using Linux, Third Edition

12. Manipulating Files (continued)
Delete files when no longer needed
rm command - permanently removes a file or an empty directory
The -r option of the rm command will remove a directory and everything it contains
Copy files as a means of back-up or as a means to assist with new file creation
cp command - copies the file(s) specified by the source path to the location specified by the destination path
Guide to UNIX Using Linux, Third Edition

13. Manipulating Files (continued)
Move files from directory to directory
mv command - removes file from one directory and places it in another
Finding a file helps you locate it in the directory structure
find command - searches for the file that has the name you specify
Guide to UNIX Using Linux, Third Edition

14. Manipulating Files (continued)
Combining files using output redirection
cat command - concatenate text of two different files via output redirection
paste command - joins text of different files in side by side fashion
Guide to UNIX Using Linux, Third Edition

15. Manipulating Files (continued)
The paste command joins text of different files in side by side fashion
Guide to UNIX Using Linux, Third Edition

16. Manipulating Files (continued)
Extracting fields of a file using output redirection: the cut command removes specific columns or fields from a file
Guide to UNIX Using Linux, Third Edition

17. Manipulating Files (continued)
Sorting the contents of a file
sort command - sorts a file’s contents alphabetically or numerically
the sort command offers many options:
You can sort the contents of a file and redirect the output to another file
Utilizing a sort key provides the option of sorting on a field position within each line
Guide to UNIX Using Linux, Third Edition

18. Manipulating Files (continued)
Guide to UNIX Using Linux, Third Edition

19. Creating Script Files
UNIX/Linux users create shell script files to contain commands that can be run sequentially as a set – this helps with the issues of command automation and re-use of command actions
UNIX/Linux users use the vi editor to create script files, then make the script executable using the chmod command with the x argument
Guide to UNIX Using Linux, Third Edition

20. Creating Script Files (continued)
Guide to UNIX Using Linux, Third Edition

21. Using the join Command on Two Files
Sometimes you want to link the information in two files
The join command is often used in relational database processing
The join command associates information in two different files on the basis of a common field or key in those files
Guide to UNIX Using Linux, Third Edition

22. A Brief Introduction to the Awk Program
Awk, a pattern-scanning and processing language helps to produce professional-looking reports
Awk provides a powerful programming environment that can perform actions on files that are difficult to duplicate with a combination of other commands
Guide to UNIX Using Linux, Third Edition

23. A Brief Introduction to the Awk Program (continued)
Awk checks to see if the input records in specified files satisfy a pattern
If so, awk executes a specified action
If no pattern is provided, awk applies the action to every record
Guide to UNIX Using Linux, Third Edition

24. Chapter Summary
UNIX/Linux supports regular files, directories, and character and block special files
File structures depend on data being stored
UNIX/Linux receives input from the standard input device (keyboard, stdin) and sends output to the standard output device (monitor, stdout)
Guide to UNIX Using Linux, Third Edition

25. Chapter Summary (continued)
touch updates a file’s time and date stamps and creates empty files
rmdir removes empty directories
cut extracts specific columns or fields from a file
paste combines two or more files
sort sorts a file’s contents
Guide to UNIX Using Linux, Third Edition

26. Chapter Summary (continued)
To automate command processing, include commands in a script file
join extracts data from two files sharing a common field and uses this field to join the two files
Awk is a pattern-scanning and processing language useful for creating a formatted report with a professional look
Guide to UNIX Using Linux, Third Edition