1. Advanced File Processing
Chapter Five
Advanced File Processing

2. Selecting, Manipulating, and Formatting Information
Lesson A
Selecting, Manipulating, and Formatting Information

3. Objectives
Use the pipe operator to redirect the output of one command to another command
Use the grep command to search for a specified pattern in a file
Use the uniq command to remove duplicate lines from a file

4. Objectives Use the comm and diff commands to compare two files
Use the wc command to count words, characters and lines in a file
Use the manipulate and format commands: sed, tr, and pr

5. Advancing Your File Processing Skills
The select commands, which extract data

6. Advancing Your File Processing Skills
The manipulation and transformation commands alter and transform into useful and appealing formats data

7. Using the Select Commands
Select commands: grep, diff, uniq, comm, wc
Using Pipes – The pipe operator (|) redirects the output of one command to the input of another command
An example would be to redirect the output of the ls command to the more command
The pipe operator can connect several commands on the same command line

8. Using Pipes
Using pipe operators and connecting commands is useful when viewing directory information

9. Using the grep Command
Used to search for a specific pattern in a file, such as a word or phrase
grep’s options and wildcard support allow for powerful search operations
You can increase grep’s usefulness by combining with other commands, such as head or tail

10. Using the grep Command
grep can take input from other commands and also be directed to provide input for other commands

11. Using the uniq Command Removes duplicate lines from a file
It compares only consecutive lines, therefore uniq requires sorted input
Uniq has an option that allows you to generate output that contains a copy of each line that has a duplicate

12. Using the comm Command
Used to identify duplicate lines in sorted files
Unlike uniq, it does not remove duplicates, and it works with two files rather than one
It compares lines common to file1 and file2, and produces three column output
Column one contains lines found only in file1
Column two contains lines found only in file2
Column three contains lines found in both files

13. Using the diff Command
Attempts to determine the minimal changes needed to convert file1 to file2
The output displays the line(s) that differ
The associated codes in the output indicate that in order for the files to match, specific lines must be added or deleted

14. Using the wc Command
Used to count the number of lines, words, and bytes or characters in text files
You may specify all three options in one issuance of the command
If you don’t specify any options, you see counts of lines, words, and characters (in that order)

15. Using the wc Command The options for the wc command: –l for lines
–w for words
–c for characters

16. Using the Manipulate and Format Commands
These commands are: sed, tr, pr
Used to edit and transform the appearance of data before it is displayed or printed

17. Introducing sed
sed is a UNIX editor that allows you to make global changes to large files
Minimum requirements are an input file and a command that lets sed know what actions to apply to the file
sed commands have two general forms
Specify an editing command on the command line
Specify a script file containing sed commands

18. Introducing sed
The many options of sed allow you to create new files containing the specific data you specify

19. Translating Characters Using the tr command
tr copies data from the standard input to the standard output, substituting or deleting characters specified by options and patterns
The patterns are strings and the strings are sets of characters
A popular use of tr is converting lowercase characters to uppercase

20. Using the pr Command to Format Your Output
pr prints specified files on the standard output in paginated form
By default, pr formats the specified files into single-column pages of 66 lines
Each page has a five-line header, its latest modification date, current page, and five-line trailer consisting of blank lines

21. Using the pr Command to Format Your Output

22. Using the pr Command to Format Your Output

23. Lesson B
Using UNIX File-Processing Tools
to Create an Application

24. Objectives Design a new file-processing application
Design and create files to implement the application
Use awk to generate formatted output

25. Objectives
Use cut, sort, and join to organize and transform selected file information
Develop customized shell scripts to extract and combine file data
Test individual shell scripts and combine all scripts into a final shell program

26. Designing a New File-Processing Application
The most important phase in developing a new application is the design
The design defines the information an applications needs to produce
The design also defines how to organize this information into files, records, and fields, which are called logical structures

27. Designing Records
The first task is to define the fields in the records and produce a record layout
A record layout identifies each field by name and data type (numeric or nonnumeric)
Design the file record to store only those fields relevant to the record’s primary purpose

28. Linking Files with Keys
Multiple files are joined by a key – a common field that each of the linked files share
Another important task in the design phase is to plan a way to join the files
The flexibility to gather information from multiple files comprised of simple, short records is the essence of a relational database system. UNIX provides several commands providing this flexibility

30. Creating the Programmer and Project Files
With the basic design complete, you now implement your application design
UNIX file processing predominantly uses flat files. Working with these files is easy, because you can create and manipulate them with text editors like vi and Emacs

32. Formatting Output The awk command is used to prepare formatted output
For the purposes of developing a new file-processing application, we will focus primarily on the printf action of the awk command

33. Formatting Output
Awk provides a shortcut to other UNIX commands

34. Using a Shell Script to Implement the Application
Shell scripts should contain:
The commands to execute
Comments to identify and explain the script so that users or programmers other than the author can understand how it works
Use the pound (#) character to mark comments in a script file

35. Running a Shell Script
You can run a shell script in virtually any shell that you have on your system
The Bash shell accepts more variations in command structures that other shells
Run the script by typing sh followed by the name of the script, or make the script executable and type ./ prior to the script name

36. Putting it all together to Produce the Report
An effective way to develop applications is to combine many small scripts in a larger script file
Have the last script added to the larger script print a report indicating script functions and results

37. Putting it all together to Produce the Report

38. Putting it all together to Produce the Report

39. Chapter Summary
The UNIX file-processing commands can be organized into two categories: (1) select and (2) manipulation and transformation
The uniq command removes duplicate lines from a sorted file
The comm command compares lines common to file1 and file2, and produces output that shows the variances between the two
The diff command attempts to determine the minimal set of changes needed to convert file1 into file2

40. Chapter Summary
The tr command copies data read from the standard input to the standard output, substituting or deleting characters specified
The se command is a file editor designed to make global changes to large files
The pr command prints the standard output in pages
The design of a file-processing application reflects what the application needs to produce
Use record layout to identify each field by name and data type

41. Chapter Summary
Shell programs should contain commands to execute programs and comments to identify and explain the programs. The pound (#) character denotes comments
Write shell scripts in stages so that you can test each part before combining them into one script. Using small shell scripts and combining them in a final shell script file is an effective way to develop applications