perl functions and subroutines

8/13/2019 Perl Functions and Subroutines

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Title

Built-in Functions and

Subroutines

PERL


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Agenda

Functions

Built-in Functions

Built-in Functions by Category

Subroutines

Defining Subroutines

Returning Values

Using Arguments

Passing Arrays and Hashes by ReferenceHandling return Values


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Built-in Functions

Terms in an expression along with literals andvariables

Can be used either with or without parenthesesaround their arguments


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Built in Functions by Category

Text processing related built-in functions

chomp();#used for removing line terminators

Example:-

chomp($_);#removes new line character from current lineFor arrays, hashes and strings

chop();#used for chopping of one character from string end

Example:-

$name = Prashanth;

for($i=1;$i


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Continued

length();#Gets length of string

Example:-

length($string);

split ();

Example:-

while () {

chomp; # avoid \n on last field

@array = split /:/ , $_; # split current line delimited by :

#& push them in array @array

}

Push, pop, shift, unshift();

Example:-

Push(@array1, @array2) is better than @array1 = (@array1, @array2)


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Built-in Functions Partial List

Functions for SCALARs or stringschomp, chop, chr, crypt, hex, index, lc, lcfirst, length, oct, ord, reverse, rindex,

sprintf, substr, tr///, uc, ucfirst,

Regular expressions and pattern matching

m//, pos, quotemeta, s///, split, study, qr//

Numeric functionsabs, atan2, cos, exp, hex, int, log, oct, rand, sin, sqrt, srand

Functions for real @ARRAYs

pop, push, shift, splice, unshift

Functions for list data

grep, join, reverse, sort

Functions for real %HASHes

delete, each, exists, keys, values


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Built-in Functions (cont.)

Input and output functions

binmode, close, closedir, dbmclose, dbmopen, die, eof, fileno, flock, format, getc,print, printf, read, readdir, rewinddir, seek, seekdir, select, syscall, sysread,sysseek, syswrite, tell, telldir, truncate, warn, write

Functions for filehandles, files, or directories

-X, chdir, chmod, chown, chroot, fcntl, glob, ioctl,

link, lstat, mkdir, open, opendir, readlink, rename,

rmdir, stat, symlink, umask, unlink, utime

Keywords related to the control flow of your perl program

caller, continue, die, do, dump, eval, exit, goto, last, next, redo, return, sub

Keywords related to perl modules

do, import, no, package, require, use

Functions for processes and process groups

alarm, exec, fork, getpgrp, getppid, getpriority, kill, pipe, qx/STRING/, setpgrp,setpriority, sleep, system, times, wait, waitpid


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Use the chop() function in a program. Printboth the returned character and the stringthat was passed as a parameter.

Write a program that shows what the shift()and unshift() functions do.

Modify the program to show what the push()and pop() functions do.


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Subroutines

User written functions

Are called like functions

Makes code clean

Code reuse

Called in program as

&sub_name Old methodsub_name(); New method


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Defining Subroutines

Use the keyword subfollowed by name

followed by a code block

Exampleprint I am not in subroutine\n;

print Enter Your Name\n;

$name = ;

chomp($name);

print Calling subroutine\n;

&print_my_name($name);

print Finally I am out of subroutine\n;

sub print_my_name

{

print I am @_ and I am in subroutine now\n;

}


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Returning Values

Example:

use strict;

sub HowdyEveryone {

return "Hello everyone.\nWhere do you want to go with Perl

today?\n";}

print &HowdyEveryone;


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Using Arguments

Perl sets a special array variable, @_Declare a list of variables and assign @_

Example:

use strict;

sub HowdyEveryone {

my($greeting, @names) = @_;

my $returnString;

foreach my $name (@names) {

$returnString .= "$greeting, $name!\n";

}

return $returnString ."Where do you want to go with Perl today?\n";

}

print &HowdyEveryone ("Hello!", "Prashanth", "Santosh", "Smitha", "Alia", "Anupama");


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Exercise-Subroutine

Write a subroutine to get the sum,multiplication and division of 2 numbers.

Call the subroutine with capturing the returnvalues in scalar variables and also returnvalues.

After this is done, just modify the program toget inputs from the command line.

(Hint: ARGV is the array which stores all the command line inputs)


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ImaginationAction Joy

perl functions and subroutines

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