perl FAQ(zz)

陈银山

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 andvalues.
4. How would you replace a char in stringand how do you store the number of replacements?
　　Ans : By using Translation operator(tr///). Number of replacements can be obtained by assigning wholeexpression to scalar variable.
5. How do you open a file forwriting?
　　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 followingserve: -w, strict, - T ?
　　Ans : List out the warnings if any in perlprogram.
8. Explain the difference between use andrequire?
　　Ans : "use" the controler will go to thatfile during run time and come back to original program at the sametime if we consider the "require" the         wholefile will get copied at the place where it is required.
9. Explain the difference between my andlocal?
　　Ans : The variables declared with "my" canlive only within the block it was defined.
The variables declared with "local" can live within the block andhave its visibility in the functions called within thatblock.
10. Which is the shebang inperl?
　　Ans : #! /usr/bin/perl
11. Name the two phases of execution ofPERL program?
　　Ans : Compiler phase and Runphase.
12. Which is the default variable inPERL?
　　Ans : $_
13. How to check the syntax of the scriptwithout executing the program?
　　Ans : #! /usr/bin/perl -c
14. How to get the versionPERL?
　　Ans : #! /usr/bin/perl -v
15. Which is the command used to changethe base of a number to another base?
　　Ans : sprintf
16. Which is the command used to removethe new line character?
　　Ans : chomp();
17. How we can get ASCII value ofcharacter?
　　Ans : Ord();
18. What is QW in list and why it isused?
　　Ans : QW is quote word which mainly usedto avoid complexity in lists.
19. Give an example to show how the mapwill be used for list?
　　Ans : print ( map lc ,A,B,C);
20. How array differs from list
　　Ans : Array is obtained by assigning listto variable.
21. $#arrayname signifies
　　Ans : Last index of an array.
22. How we can get the size of anarray?
　　Ans : By assigning an array to any scalarvariables.
23. What are the functions of followingcommands:
a. push    b. pop    c. shift    d. unshift
　　Ans : a. push = updates the values at theend 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 anarray.
24. Give an example to show how splicingwill be done?
　　Ans : @num = (1,2,3,4,5);
@val = (6,7);
splice (@num ,4,0,@val);
25. How we can access the individualvalues of hash?
　　Ans : Using {}
26. How to find the number of keys andvalues in hash?
　　Ans : Using key words Keys andValues.
27. Which is the function used to deletethe value of specified key?
　　Ans : undef
28. Which is the function to delete bothkey and related value?
　　Ans : delete
29. What & specifies inPERL?
　　Ans : Bitwise and
30. Which is the binding operater inPERL?
　　Ans “ =~”
31. What are the functions of followingkeywords
a. last    b.next    c.redo
　　Ans : a. last : used to exit from thestatement block.
b. next : used to skip the rest of the statements block and startthe next iteration.
c. redo : causes perl to restart the current statementblock.
32. List the regular expressions inPERL?
　　Ans : m// , s/// ,tr///
33. How to pass an arguments tosubroutines?
　　Ans : Through variable @_.
34. Which is the default variable thatwill be having argument value that is passed tosubroutine?
　　Ans : @_
35. What happens if a PATTERN is of nullstring?
　　Ans : Last successfully executed regularexpression is used.
36. $value=~tr/SEARCHLIST/REPLACEMENTLIST/in this expression what will be the variable $valuehaving?
　　Ans : SEARCHLIST
37. $value=~tr/SEARCHLIST/REPLACEMENTLIST/how to find out the number of replacements in thisexpression?
　　Ans : By assigning this expression toanother variable like
$count=($value=~tr/SEARCHLIST/REPLACEMENTLIST/)
38. How to complement the the search listin Translation operator?
　　Ans : Using c modofier
39. How we can match the metacharacters inpattern matching?
　　Ans : m/\metacharacter/
40. $var=~/\d/ What does itmatch?
　　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 beused to match white space?
　　Ans : \s
43. What is the difference between \u and\U?
　　Ans : \u changes next character touppercase.
\U changes following characters to uppercase.
44. What is the difference betweenfollowing expressions
$var=~/w[^aoi]nder/ &$var=~/^w[aoi]nder/
　　Ans : first one will look for W followedby 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 arethe values of following variables
$txt ,    $1,    $2,    $3
　　Ans : $1 = Testing, $2=T,$3=ing
46. What are Quantifiers?
　　Ans : Quantifiers says how many timessomething may match.
47. Which of the following matches zero ormore times
a. *     b. +   c. ?   d.{}
　　Ans : a
47. How we can find out number ofarguments sent from command line?
　　Ans : Assigning @ARGV to any scalarvariables.
48. What are the difference in writingscript in C and PERL?
　　Ans : There we don't have a muchdifference between PERL and shell script.
As of my knowledge both are good in there own way of workenvironment.
As consern to speed & performance the PERL is ahead of shell.
---Perl is very good at text processing like we have regularexpressions.
---Shell scripts are mainly inteded for sys-admin tasks.
49. How we can use a Linux commands inPERL?
　　Ans : By writing linux command in ``operater.
50. Write a script to set an environmentvariables?
　　Ans : $var = `setenv $VAR path`;
51. How we can use foreach loop foraccessing the content of file?
　　Ans : foreach (< HANDLER>) {
command1;
command2;
....... }
52. Write a script to list all unknowndirectories of another directory?
　　Ans : chdir(dir name);
$var = `find . -type d -name “*” | tee list `;