perl FAQ(zz)

1. Why do you write a program in Perl?

Ans : Easy to use and fast execution since perl script undergoes only two phases like compile phase and run phase.

2. What is the difference between chop & chomp functions in perl?

Ans : Chop removes last character.
Chomp removes new line character.

3. What is a hash?

Ans : It is array having attributes and
values.

4. How would you replace a char in string
and how do you store the number of replacements?

Ans : By using Translation operator
(tr///). Number of replacements can be obtained by assigning whole
expression to scalar variable.

5. How do you open a file for
writing?

Ans : open HANDLER, “<
filename” or die $!;

6. What is the difference between for
& foreach?

Ans : Only syntax differs.

7. What purpose does each of the following
serve: -w, strict, - T ?

Ans : List out the warnings if any in perl
program.

8. Explain the difference between use and
require?

Ans : "use" the controler will go to that
file during run time and come back to original program at the same
time if we consider the "require" the
         whole
file will get copied at the place where it is required.

9. Explain the difference between my and
local?

Ans : The variables declared with "my" can
live only within the block it was defined.
The variables declared with "local" can live within the block and
have its visibility in the functions called within that
block.

10. Which is the shebang in
perl?

Ans : #! /usr/bin/perl

11. Name the two phases of execution of
PERL program?

Ans : Compiler phase and Run
phase.

12. Which is the default variable in
PERL?

Ans : $_

13. How to check the syntax of the script
without executing the program?

Ans : #! /usr/bin/perl -c

14. How to get the version
PERL?

Ans : #! /usr/bin/perl -v

15. Which is the command used to change
the base of a number to another base?

Ans : sprintf

16. Which is the command used to remove
the new line character?

Ans : chomp();

17. How we can get ASCII value of
character?

Ans : Ord();

18. What is QW in list and why it is
used?

Ans : QW is quote word which mainly used
to avoid complexity in lists.

19. Give an example to show how the map
will be used for list?

Ans : print ( map lc ,A,B,C);

20. How array differs from list

Ans : Array is obtained by assigning list
to variable.

21. $#arrayname signifies

Ans : Last index of an array.

22. How we can get the size of an
array?

Ans : By assigning an array to any scalar
variables.

23. What are the functions of following
commands:
a. push
    
b. pop
    
c. shift
    
d. unshift

Ans : a. push = updates the values at the
end of an array.
b. pop = takes out the last element of an array.
c. shift =takes out the first element of an array.
d. unshift = updates the values at the beginning of an
array.

24. Give an example to show how splicing
will be done?

Ans : @num = (1,2,3,4,5);
@val = (6,7);
splice (@num ,4,0,@val);

25. How we can access the individual
values of hash?

Ans : Using {}

26. How to find the number of keys and
values in hash?

Ans : Using key words Keys and
Values.

27. Which is the function used to delete
the value of specified key?

Ans : undef

28. Which is the function to delete both
key and related value?

Ans : delete

29. What & specifies in
PERL?

Ans : Bitwise and

30. Which is the binding operater in
PERL?

Ans “ =~”

31. What are the functions of following
keywords
a. last    b.
next    c.
redo

Ans : a. last : used to exit from the
statement block.
b. next : used to skip the rest of the statements block and start
the next iteration.
c. redo : causes perl to restart the current statement
block.

32. List the regular expressions in
PERL?

Ans : m// , s/// ,tr///

33. How to pass an arguments to
subroutines?

Ans : Through variable @_.

34. Which is the default variable that
will be having argument value that is passed to
subroutine?

Ans : @_

35. What happens if a PATTERN is of null
string?

Ans : Last successfully executed regular
expression is used.

36. $value=~tr/SEARCHLIST/REPLACEMENTLIST/
in this expression what will be the variable $value
having?

Ans : SEARCHLIST

37. $value=~tr/SEARCHLIST/REPLACEMENTLIST/
how to find out the number of replacements in this
expression?

Ans : By assigning this expression to
another variable like
$count=($value=~tr/SEARCHLIST/REPLACEMENTLIST/)

38. How to complement the the search list
in Translation operator?

Ans : Using c modofier

39. How we can match the metacharacters in
pattern matching?

Ans : m/\metacharacter/

40. $var=~/\d/ What does it
match?

Ans : Matches any digit.

41. $var=~/\W/ it is equivalent to
a. [a-z]     b.
[a-zA-Z]     c.
[^0-9a-zA-Z]    
d. [0-9]

Ans : C

42. Which is the character that will be
used to match white space?

Ans : \s

43. What is the difference between \u and
\U?

Ans : \u changes next character to
uppercase.
\U changes following characters to uppercase.

44. What is the difference between
following expressions
$var=~/w[^aoi]nder/ &
$var=~/^w[aoi]nder/

Ans : first one will look for W followed
by something that is none of 'a' , 'o' , or 'i'
second one will matches at the begining of the line.

45. $txt=~/((T/N)est(ing|er))/) What are
the values of following variables
$txt ,
    $1
,
    $2
,
    $3

Ans : $1 = Testing, $2=T,
$3=ing

46. What are Quantifiers?

Ans : Quantifiers says how many times
something may match.

47. Which of the following matches zero or
more times
a. *     b. +
   c. ?
   d.
{}

Ans : a

47. How we can find out number of
arguments sent from command line?

Ans : Assigning @ARGV to any scalar
variables.

48. What are the difference in writing
script in C and PERL?

Ans : There we don't have a much
difference between PERL and shell script.
As of my knowledge both are good in there own way of work
environment.
As consern to speed & performance the PERL is a
head of shell.
---Perl is very good at text processing like we have regular
expressions.
---Shell scripts are mainly inteded for sys-admin tasks.

49. How we can use a Linux commands in
PERL?

Ans : By writing linux command in ``
operater.

50. Write a script to set an environment
variables?

Ans : $var = `setenv $VAR path
`;

51. How we can use foreach loop for
accessing the content of file?

Ans : foreach (< HANDLER
>) {
command1;
command2;
....... }

52. Write a script to list all unknown
directories of another directory?

Ans : chdir(dir name);
$var = `find . -type d -name “*” | tee list `;