Shell Scripting Interview Questions

in bash:

cat $filename | awk {print $25 }

a simple perl one liner to print only the 25th line

Code
perl -ne $. == 25 && print && exit

cat file_name | cut -c 10-20

head -20 | tail -10

cat file_name | awk {print $n} # where N is the column no. and tab is field seperator

cat SO_02052012_2.csv | awk -F; {print $n} # where N is is column no. and semicolon is field seperator

path=${1?pls provide the path to script}
cd $path
for i in *
do
mv $i ${i}.new
if [ $? -eq 0 ]
then
echo "file rename successful"
ls -l ${i}*
fi
done

for file in /dxusers/testing/test_delete/*
do
 if [ -f $file ]
 then
  mv $file $file.new
 fi
done

Positional parameters are reads either by displaying there value or can be assigned to another variables.

echo $1 $2 $9 ${10} ${20}
shift operators can be used to move around the positional parameters.

example: test.sh 1 2 3 4 5

a=$1

while [ -z "$a" ]
do

echo $a
shift

done

echo $1
echo $2

$# : Stands for counts of the number of the positional parameters passed to a script.

example test.sh 1 2 3 4 5 6 7 , there are 7 paramaters as passed so the count of the $# is 7

By using $# parameter, the program checks whether the right number of arguments have been entered.

$? returns the status of the last command executed . if the last command is successfull then it will 0 , otherwise it will retrun non-zero. ex: date ; echo $? or try this dte ; echo $?

UNIX commands (well the "well behaved" ones) give a return code between 0 and 127 (inclusive). General convention is that a return code of 0 (zero) indicates success and that a non-zero return code i...

grep "^$" filename

grep -c "^$" file name


here -c option count the no.of empty line..the anchors denotes the empty line from your file name

awk NR==

cut -d -f2

:1,$s/n/xyz/g

All the sed replacements are by default global. It's in the vi editor that you have to specifically give "g" for global replacement.

Current_time=`date +%H%M`
who -u | awk $Current_time - $4 <= 5 { print }

last -5|grep -i "logged in"|wc -l
last -5|grep -v "logged out"|wc -l

Code
mailx -s "<subject>" <email_id list> < <input_file>

The following is a more detailed example for using mailx in shell script. This should help.

Code
SUBJECT="Email Subject Line"
TO=xyz@company.com
CC=`tr '
' ', ' < mailCClist.txt`
#BCC="xyz2@comp.com"
 
echo "Send the E-mail message..."
/usr/bin/mailx -s "${SUBJECT}" ${TO} <<-END
 
~< ! uuencode $DCdir/$FileName "Result.txt"
 
~c ${CC}
~b ${BCC}
        Hi,
 
        Blah, Blah.. body of the email.
 
        Thanks
        Satya
        ~.
        END
 
echo "Mail Sent!!"
 

Code
uuencode attachment1 attachment1 | mailx -c x@yz.com,a@bc.com -s "subject" m@no.com 

You should be able to use something like the following example to get the CC option working with mailx. Preferably create a list of users needed to be put in the CC option (as mailCClist.txt in the ex...

in vi editor
vi connect.sh
#!/bin/bash

sqlplus -s sys as sysdba < startup
spool on;
spool ashu;
connect scott/tiger
select * from emp;
spool off;
exit;
EOF
cat ashu

sqlplus -s username/password@schema name
:wq

You can read the contents of file inside jar without extracting in shell script by using:

tar -tvf file.tar

jar tvf jarName.jar

Using KSH while loop#!/bin/ksh
#Get the count of total number of arguments passed while executing this script
int i = $#; #total number of arguments passed#
names=$@; #list of actual arguments passed#
while [ ${i} -gt 0 ]
do
echo '${names[i]}';
i=`expr i - 1`;
done
exit 0;

$ cat rev2
i=$#
echo "$@" > file_1

while [ $i -gt 0 ]
do
cut -f $i -d" " file_1 >> file_2
i=`echo $i-1|bc`
done

echo `cat file_2`;
rm -f file_1 file_2;

$ sh rev2 A B C D E
E D C B A

Code
echo $1
echo $2
echo $3

Try this:

echo "one two three" | xargs

the output is: one two three

a) vi /etc/default/login
comment the line of /dev/console

b)vi .rhosts
enter the hostname by which the only user can connect with your system....bt no one else.....
c) disable the ftp for the selected users in /etc/ftpusers file ...

Unix is having 3 ways of Security Mechanism:1. By granting or revoking File permissions. Owner or Admin can change permissions to be given to group or others by using chmod command in Unix.2. Login is...

in 2 ways it can be done:
1st way
$ echo $?  

2nd way:

$ pwd 2> error| cat error|wc -l
       0
$ cat h 2> error| cat error|wc -l
       1

pwd or cat or any command if outpt is 0 then successful else failed.