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 `;