Shell Scripting Interview Question & Answers
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Q: What is a shell?
Shell is a interface between user and the kernel. Even though there can be only one kernel ; a system can have many shell running simultaneously . Whenever a user enters a command through keyboard the shell communicates with the kernel to execute it and then display the output to the user.
Q: What are the different types of commonly used shells on a typical linux system?
csh,ksh,bash,Bourne . The most commonly used and advanced shell used today is “Bash” .
Q : What is the equivalent of a file shortcut that we have on window on a Linux system?
Shortcuts are created using “links” on Linux. There are two types of links that can be used namely “soft link” and “hard link”
Q: What is the difference between soft and hard links?
Soft links are link to the file name and can reside on different filesytem as well; however hard links are link to the inode of the file and has to be on the same filesytem as that of the file. Deleting the orginal file makes the soft link inactive (broken link) but does not affect the hard link (Hard link will still access a copy of the file)
Q: How will you pass and access arguments to a script in Linux?
Arguments can be passed as:
scriptName “Arg1” “Arg2”….”Argn” and can be accessed inside the script as $1 , $2 .. $n
Q: What is the significance of $#?
$# shows the count of the arguments passed to the script.
Q: What is the difference between $* and $@?
$@ treats each quoted arguments as separate arguments but $* will consider the entire set of positional parameters as a single string.
Q: How will you find the 99th line of a file using only tail and head command?
tail +99 file1|head -1
Q:In my bash shell I want my prompt to be of format ‘$”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
Q: 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.
Q: How can you find out how long the system has been running?
Q: 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.
Q: 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.
Q: 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.
Q: 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:
Above copies file file1 from local system to destination system whose hostname is specified.