Faq In Unix

How would you get the character positions 10-20 from a text file? ANS cat filename.txt | cut -c 10-20

How would you print just the 25th line in a file (smallest possible script please)? ANS sed -n '25p' filename.txt How To Connect To Data Base in Solaris

echo "Enter User Name "read nameecho "Enter passwd "stty -echoread passstty echo sqlplus -s $name@oracle/$pass< How would you print just the 25th line in a file (... head -25 file| tail -1 goes wrong because if some one deletes some lines even then it gives last line as 25th line. so the right option is tail +25 file| head -1 tail -n +25Â | head -1 OR head -n 25 | tail -1

How would you replace the n character in a file with some xyz? sed 's/n/xyz/g' filename > new_filename RE: How would you replace the n character in a file wi... vi file name then go to command mode %s/n/xyz/g How would you replace the n character in a file wi... tail -1 sample.txt | sed 's/.$/xyz/'Check this

What does $? return? Will return the status of the command which is executed lastly. 0 => Success 2 => Error $? will return exit status of command .0 if command gets successfully executed ,non-zero if command failed.

What does $# stand for?

$# returns the number of parameters that are passed to a shell script $? returns the exit code of the last executed command (0 : Successful, 1 or other: Failed)

What is $*?

Will display all the commandline arguments that are passed to the script Its mainly used for showing up all params. i.e - if you execute script in following way to which we are trying to pass 4 params ./test.sh 1 "hello world" 2 "test" and if we print inside script echo $* it will print null1 hello world 2 testnull $1: the 1st parameter $2: the 2nd parameter ... $* All parameters in the command line $* displays values of all positional parameters set

If you have a string "one two three", Which shell command would you use to extract the strings? echo "one two three" | cut -d" " -f 1,2,3 or echo "one two three" | awk '{print $1 $2 $3}'

echo $string | cut -d" " -f1 echo $string | cut -d" " -f2 echo $string | cut -d" " -f3

echo "one two three" | cut -d" " -f 1,2,3 or echo "one two three" | awk '{print $1 $2 $3}' sed and awk echo "one two three" | while read ONE TWO THREE print $ONE one print $TWO two print $THREE three

What is the difference between a shell variable that is exported and the one that is not exported? try this simple script it will clear your concept :script a.sh :---------export A=3 B=5 sh b.sh -------script b.sh :----------echo "exported variable $A is :- $A"

echo "Variable $B -- $B " --------A persists in b.sh whereas B doesn't.

exported variable is visible to the child processes while the normal variables are not. The Shell variable which is exported would available to all the programs outside the Shell also. And the shell variable which is not exported, would available for that shell or for the shell program only, in which the variable is declared.

How will you list only the empty lines in a file (using grep)? grep "^$" filename.txt OR grep -c "^$" filename.txt OR grep "^[

]*$" filename.txt

In character set (between [ and ] one space and tab is given) this command will gives all the blank line including those having space and tabs (if pressed)only

OR We can do this efficiently through awk script awk '{ if (NF == 0) { print "Here comes the empty line" print $0 } }' filename NF=number of fields in the current line $0=current line

How do you schedule a command to run at 4:00 every morning? by using cron job OR Schedule the Job using crontab..From the command prompt perform a "man" on crontab and then type in crontab -e to create a new "job" OR do first crontab -e and then add a line like below 0 4 * * * name of the command OR

Step 1. Set environemen variable EDITOR=vi if not set Step 2. Give command

crontab -e

Step 3. Add following entry at the end 0 4 * * *

OR This is done by 'at' command in HPUX and Sun solaris or 'cron' command can be used too. Mukesh Chauhan –Bangalore 1. There are two ways to schedule a script to run exactly at 4:00 AM every morning a: CRONTAB b. AT (at command executes only once) Crontab format * * * * * <minute> <month> command <0-59> <0-23> <1-31> <1-12> <0-7> command OR

1st step $ cat > cmdfile //<Minute> 0 4 * * Ctrl d 2nd Step crontab cmdfile

How do u open a read only file in Unix? vi filename e.g vi abc.txt but you cannot write to it easy way if file is small cat filename and contents is display on screen OR view is a better option. It will not allow writing to a file normally, unless done forcefully like "wq!" or "x!"...

"vi -R filename"

OR In a shell script, you can open a file in read only mode by using O_RDONLY Syntax - open(,O_RDONLY)

more is the best option. OR If you mean open a file in Unix which has read-only permission ... then you open it the same way you open any other file. The system will simply prevent you from writing to it. If you mean open a file in Unix such that you can not write to the file, even though you otherwise would be allowed because you do have write permission ... ... then it depends on what mechanism you use to open the file. Others have already answered for opening with the "vi" editor. Other programs, such as "emacs", or other text editors, would have other ways.

What are the different kinds of loops available in shell script? for, if, while, case Broadly categorised in 3 for while until

How do you read arguments in a shell program - $1, $2 ? #!/bin/sh for i in $* do echo $i done On executig the above script with any number of command-line arguments it will display all the parametsrs. OR $1 would be the first command line argument, $2 the second, and so on $0 is the name of the script or function OR

Shell script accepts parameters in following format... $1 : first $2 : second....so on upto $9 : 9th param whereas $0 : gives script/function name If your script has more than 9 params then accept in following way... ${12} : 12th param ${18} : 18th param OR

by using : exec<$1 or exec<$2

When you login to a c shell, which script would be run first? (before the terminal is ready for the user) For C shell , first /etc/.login script is run & after that ~/.login is run & then ~/.cshrc is run. OR .profile file will execute first when a user logs in.

OR For C shell , first /etc/.login script is run & after that ~/.login is run & then ~/.cshrc is run.