UNIX for Dummies Questions & Answers

Hi all
today i gone through worst interview of my life that for hour questions were so basic but i never though about them now i am figuring out answers my self but i would appreciate if you ppl help me ... i am listing some of the questions i remember ..

1 )

Code:

$ cat a.sh
#! /usr/bin/ksh
echo "hello world"

$ bash a.sh

now which shell will execute this echo statement ?

2 ) how to call one shell script from other script without creating new process ? interviewer told me i want to use $aaa from a.sh script to b.sh without exporting it ?

ANSWER

Code:

$ cat a.sh
a=hello
export b=world
. b.sh

$ cat b.sh
echo "$a"
echo "$b"

$ ./a.sh
hello
world

$ cat a.sh # modified 
a=hello
export b=world
b.sh

$ ./a.sh

world
$

3 ) how to know current shell you are working in ?
echo $SHELL ...but he was looking for something else ..i dont know what exactly.

Code:

ps $$

sorry for not searching the forum before posting questions here is the thread : https://www.unix.com/unix-dummies-que...ent-shell.html

4 ) how to display all ENV varaibles without using env command ? from shell and then from perl ( perl i will figure out ..)

Code:

#! /usr/bin/perl
use Env ;
foreach $key (sort keys(%ENV)) {
      print "$key = $ENV{$key}\n";
   }

i knew this one i was not sure ..

5 ) in perl say i have statement

Code:

 chomp ( $a = `grep "abcd" a.txt` ) ;

will it assign STDOUT / STDERR / BOTH ? if not BOTH then how to get other one ?

ANSWER : it read both

Code:

$ cat a.pl
#! /usr/bin/perl

print STDOUT "THIS IS PRINTED ON STDOUT\n" ;
print STDERR "THIS IS PRINTED ON STDERR\n" ;
$
$ cat b.pl
#! /usr/bin/perl

chomp ( $a =`perl a.pl`) ;
print "$a\n" ;

$ perl a.pl > a.txt
THIS IS PRINTED ON STDERR

$ perl a.pl > a.txt 2>&1

$ perl b.pl
THIS IS PRINTED ON STDERR
THIS IS PRINTED ON STDOUT
$

6 ) in perl what can be maximum length of variable ? like my $a = "aaa...." how far can i go ?
@ corona688 - you are right ... looks like there is no limit

Code:

my $i = 0 ;
my $Char = a ;

while ( $i < 3000000 )
{
    $Var .= ${Char} ;
    $i++ ;
}

$count = length ($Var) ;
print "variable : [$Var]\n" ;
print "can print upto $count\n" ;

above script worked ...without any probs ..3 million is more than enough

7 ) in perl how can i execute a module ? and how can i use variable used in modul a in module b ?

ANSWER :

suppose i have module "A" and variable "aaa" inside it i want to access "$aaa" in B module then i would use something like
$bbb = $A::aaa ;

read it on perlmod man page ....

i can remember this much only right now ... if i find out i will put answers in this thread only ...

@ MOD : this is not homework. if this is against rules of forum you can delete this thread.

Korn shell - ksh


The rest of your questions I will leave to people with better knowledge...sounds like it was a tough interview.

Just work it out logically. What does bash do when you run 'bash filename'? How will it treat lines beginning with #? 'source filename'. I don't think perl has a real limit.

Dont understand.. Is he thinking of exec ?

Well in ksh I would type :

Code:

# set

1. bash
2. use the dot command to invoke the script
3. ps -f
4. In ksh I would use "typeset -x". Also there is "printenv".

I'm not real good at perl, but I think....
5. stdout; 2>&1
6 and 7: I'll pass

When you say:
bash file
bash will open the file and start reading commands. No kernel exec happens and to any shell "#! /usr/bin/ksh" is just a comment.