IT441 Network Services Administration

1. IT441Network Services Administration Prof. Alfred J Bird, Ph.D., NBCT http://www.cs.umb.edu/~abird abird@cs.umb.edu http://it441-s14-bird.wikispaces.umb.edu/ Office – McCormick 3rd floor 607 Office Hours – Tuesday and Thursday 4:00PM to 5:15PM

2. Pipes in Perl • What is a pipe? • Why do we use pipes? • In Perl we implement pipes using the OPEN statement • open (FH, -|, ‘perl sort2.pl gettysburg.txt’); • What will this statement do? • It will start a perl program sort2.pl using the file gettysburg.txt and send the output from sort2.pl into our program under the filehandle <FH>.

3. Pipes in Perl • -| brings the output of the other program into our program via the filehandle • |- takes the output of our program and sends it to the other program using the file handle and a print statement

4. File Tests • Before we do anything we often would like to know the status of the file or directory we are working with. • We can do this with the following type of test • if (flag “somefile.dat”) {action} or • if (flag $somefile) {action}

5. File Test Flags • -e true if the file exists • -f true if a plain file – not a directory • -d true if file is a directory • -z true if file has zero size • -s true if file has nonzero size -- returns size • -r true if file is readable by you • -w true if file is writeable by you • -x true if file is executable by you • -o true if file is owned by you This is table 8-1 on page 201 in the textbook

6. File Test Practice Coding • Write a simple program to: Read in the name of a file from the keyboard Check if the file exists. Check to see if it is a directory Check to see what permissions you have on this file Print out appropriate information to the screen

7. File Test Practice Coding • Write a simple program to: Read in the name of a file from the keyboard Check if the file exists. Check to see if it is a directory Check to see what permissions you have on this file Print out appropriate information to the screen • See filetesting.pl in my home directory

8. String Processing • Remember strings are the basic data type in Perl • We have already learned one way to process a string. • We can use a regex (a regular expression) • Remember how the characters in a string are counted • The first (left most) character is 0 • The last (right most) character is -1 • There is another way to process strings in Perl • Perl has many built-in functions to process strings.

9. String Functions • Some string functions implemented in Perl • length(string) • Use this function to determine the length of the string. • index(string, substring) • Use this function to determine the 0-based location of the substring in the string. If substring is not found it returns a -1. • rindex(string, substring) • Similar to index() but starts from the right-most end. • substr(string, starting-index, length) • This function returns a substring of length number of characters starting from starting-index.

10. A Sting Function Coding Exercise • Copy string.txt from my home directory. • Write a small program that will: • Calculate the number of characters in the string using the string function length(). • Find the location of a substring entered from the keyboard. • Strip out a substring of a given length starting at a given position where the length and position are entered from the keyboard. • Print out the results to the screen.

11. A Sting Function Coding Exercise • Copy string.txt from my home directory. • Write a small program that will: • Calculate the number of characters in the string using the string function length(). • Find the location of a substring entered from the keyboard. • Strip out a substring of a given length starting at a given position where the length and position are entered from the keyboard. • Print out the results to the screen. See strfunctest.pl in my home directory for a solution

12. For next time • Read pages 196 to 205 in the textbook. • Study and try to understand the program filetest.pl on pages 201-202. See if you can enter it and make it work. • Read pages 207-213 in the textbook.