IT441

NETWORK SERVICES ADMINISTRATION

Prof. Alfred J Bird, Ph.D., NBCThttp://www.cs.umb.edu/~abird

abird@cs.umb.edu

http://it441-s14-bird.wikispaces.umb.edu/

Office – McCormick 3rd floor 607Office Hours – Tuesday and Thursday 4:00PM to

5:15PM

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>.

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

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}

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

File Test Practice Coding

Write a simple program to:Read in the name of a file from the keyboardCheck if the file exists.Check to see if it is a directoryCheck to see what permissions you have on this

filePrint out appropriate information to the screen

File Test Practice Coding

Write a simple program to:Read in the name of a file from the keyboardCheck if the file exists.Check to see if it is a directoryCheck to see what permissions you have on this

filePrint out appropriate information to the screen

See filetesting.pl in my home directory

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.

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.

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.

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

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.