Perl (Tutorial II)

1. Perl(Tutorial II) NLP Course 06 Examples

2. EXAMPLE 1 #!/usr/bin/perl #Opens and reads the file "sentences" (input file) line by line. #For the i-th sentence of input file, finds the i-th word and prints it to the screen open (IN,"sentences") || die ("can not open the input file!\n"); #open the input file $rdln=<IN>; #"load-read" the 1st sentence of input file $s_counter=0; #sentence counter while ($rdln ne "") #while the end of input file is not reached { @list=split(/\s+/,$rdln); print ($list[$s_counter],"\n"); $rdln=<IN>; #"load-read" the next sentence of input file $s_counter++; } close (IN); #close the input file

3. EXAMPLE 1 Input: a file containing the following sentences: first sentence a second sentence another simple third sentence Output: first second third

4. EXAMPLE 2 #!/usr/bin/perl #Open and reads the file "sentences" (input file) line by line. #Writes to the output file, "num_words" the following information: #" The i-th line of input file consists of X words." open (IN,"sentences") || die ("can not open the input file!\n"); #open the input file open (OUT,">num_words") || die ("can not open the output file!\n"); #open the output file $rdln=<IN>; #"load-read" the 1st sentence of input file $s_counter=0; #sentence counter while ($rdln ne "") #while the end of input file is not reached { @list=split(/\s+/,$rdln); $num=scalar(@list); print OUT ("The ",$s_counter+1," line of input file consists of ",$num," words.\n"); $rdln=<IN>; #"load-read" the next sentence of input file $s_counter++; } close (IN); #close the input file close (OUT); #close the output file

5. EXAMPLE 2 Input: a file containing the following sentences: first sentence a second sentence another simple third sentence Output: The 1 line of input file consists of 2 words. The 2 line of input file consists of 3 words. The 3 line of input file consists of 4 words.

6. EXAMPLE 3 #!/usr/bin/perl #How "my" affects the scope of a variable. $a=5; print ("Initial value of a: ",$a,"\n"); sub add { #subroutine definition #$a=$a+1; my $a=$a+1; print ("Value of a inside the subroutine: ",$a,"\n"); } &add; #subroutine call print ("Final value of a: ",$a,"\n"); #Output: #--------- #Without the use of "my" ($a=$a+1;): #initially a=5, and is increneted by 1 (a=6)! #BUT #Using "my" (my $a=$a+1;): #a remains always constant!! #a equals to 6 ONLY inside the subroutine.

7. EXAMPLE 4 #!/usr/bin/perl #Definition of a subroutine with return value, #that it takes two arguments. sub add { #subroutine definition my $a = $_[0]; #1st arg. my $b = $_[1]; #2nd arg. #in order to take the 2 arguments, we can also write: #my ($a,$b) = @_; #the list of arguments my $c; $c=$a+$b; return $c; } $res = &add(5,10); #subroutine call with 2 arguments print ("Result: ",$res,"\n"); #Output: #--------- #Result: 15

8. EXAMPLE 5 #!/usr/bin/perl sub concat { my ($a,$b,$c) = @_; #the list of arguments my $d; $d=$a.$b.$c; return $d; } $course = &concat("Natural","Language","Processing"); print ("Our course name is: ",$course,"\n"); #Output: #--------- #Our course name is: NaturalLanguageProcessing

9. EXAMPLE 6 #!/usr/bin/perl #Executes the Unix command "date". #The result is written to a file named "out_date". #This file is opened, the time is extracted and printed to the screen system ("date > out_date"); open (IN,"out_date") || die ("can not open the input file!\n"); #open the input file $rdln=<IN>; #"load-read" the 1st sentence of input file @list=split(/\s+/,$rdln); print ("The time is: ",$list[3],"\n"); close (IN); #close the input file

10. EXAMPLE 6 “out_date” file contains: Mon Mar 20 18:34:41 EST 2006 Output: The time is: 18:34:41

11. EXAMPLE 7 #!/usr/bin/perl #Executes the Unix command "date". #The result is written to a file named "out_date". #This file is opened and the month is extracted. # IF the month is March or April or May, a "spring " message is printed to the screen, ELSE #"Sorry, the Spring is not here..." system ("date > out_date"); open (IN,"out_date") || die ("can not open the input file!\n"); #open the input file $rdln=<IN>; #"load-read" the 1st sentence of input file if ($rdln =~ /(Mar|Apr|May)/) { print ("Here is Spring!!!\n"); } else { print ("Sorry, the Spring is not here...\n"); } close (IN); #close the input file