Saturday, April 13, 2013

Nitheen Kumar

Shell Scripting Interview Questions 2

 
11: How will you find the 99th line of a file using only tail and head command?

tail +99 file1|head -1

12: Print the 10th line without using tail and head command.?

sed –n ‘10p’ file1

13:In my bash shell I want my prompt to be of format ‘$”Present working directory”:”hostname”> and load a file containing a list of user defined functions as soon as I login , how will you automate this?

In bash shell we can create “.profile” file which automatically gets invoked as soon as I login and write the following syntax into it. export PS1=’$ `pwd`:`hostname`>’ .File1 Here File1 is the file containing the user defined functions and “.” invokes this file in current shell.

14: Explain about “s” permission bit in a file?

“s” bit is called “set user id” (SUID) bit. “s” bit on a file causes the process to have the privileges of the owner of the file during the instance of the program. Eg: Executing “passwd” command to change current password causes the user to writes its new password to shadow file even though it has “root” as its owner.

15: I want to create a directory such that anyone in the group can create a file and access any person’s file in it but none should be able to delete a file other than the one created by himself.?

We can create the directory giving read and execute access to everyone in the group and setting its sticky bit “t” on as follows: mkdir direc1 chmod g+wx direc1 chmod +t direc1

16: How can you find out how long the system has been running?

Command “uptime”

17: How can any user find out all information about a specific user like his default shell, real life name, default directory,when and how long he has been using the sytem?

finger “loginName” …where loginName is the login name of the user whose information is expected. 

18: What is the difference between $$ and $!?

$$ gives the process id of the currently executing process whereas $! shows the process id of the process that recently went into background.

19: What are zombie processes?

These are the processes which have died but whose exit status is still not picked by the parent process. These processes even if not functional still have its process id entry in the process table.

20: How will you copy file from one machine to other?

We can use utilities like “ftp” ,”scp” or “rsync” to copy file from one machine to other. Eg: Using ftp:  ftp hostname >put file1 >bye Above copies file file1 from local system to destination system whose hostname is specified.

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