Chapter Five Advanced File Processing

2 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

3 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

4 But first… We need to get a common file we can all work on Type the following commands: wget –U “” …and hit enter wget –U “” …and hit enter

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 less 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 ls /etc | sort –r | less

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 grep IBM /etc/termcap | head

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 About 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 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

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 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

22 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

23 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

24 Chapter Summary The tr command copies data read from the standard input to the standard output, substituting or deleting characters specified The sed command is a file editor designed to make global changes to large files The pr command prints the standard output in pages

25 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