Need help in bash scripting in Linux

ravi_nandula · 03-27-2012, 11:23 PM

Hi everyone,

I am new to linux and trying to learn scripting in linux.
My problem in scripting is.....I am not able to use if n else...can anyone pls help me....

Below is the one of the scripting which I wrote and getting errors.

To find greatest of 3 numbers.
-------------------------
#!/bin/bash
read n1
read n2
read n3
if [$n1 -gt $n2] && [$n1 -gt $n3]
echo "$n1 is greatest number"
else
if [$n2 -gt $n1] &&[$n2 -gt $n3]
echo "$n2 is greatest number"
else
echo "$n3 is greatest number"
fi
---------------------------------

kbp · 03-27-2012, 11:32 PM

The structure is "if+then, [elif+then|else], fi" .. also don't forget to leave space between your brackets and your variables

Code:

#!/bin/bash

read n1
read n2
read n3
if [ $n1 -gt $n2 ] && [ $n1 -gt $n3 ]
then
  echo "$n1 is greatest number"
elif [ $n2 -gt $n1 ] && [ $n2 -gt $n3 ] 
then
  echo "$n2 is greatest number"
else
  echo "$n3 is greatest number"
fi

chrism01 · 03-27-2012, 11:35 PM

You should really have said what errors you were getting.
Try adding 'set -xv' thus to debug

Code:

#!/bin/bash
set -xv

read n1
read n2
read n3
if [$n1 -gt $n2] && [$n1 -gt $n3]
echo "$n1 is greatest number"
else
if [$n2 -gt $n1] &&[$n2 -gt $n3]
echo "$n2 is greatest number"
else
echo "$n3 is greatest number"
fi

Basically, you need spaces around such thyings as '[', ']' etc.
Each if..then.. must end with 'fi', you also want to consider elif

my version

Code:

#!/bin/bash
read n1
read n2
read n3
if [[ $n1 -gt $n2 ]] && [[ $n1 -gt $n3 ]]
then
    echo "$n1 is greatest number"
elif [[ $n2 -gt $n1 ]] && [[ $n2 -gt $n3 ]]
then
    echo "$n2 is greatest number"
else
    echo "$n3 is greatest number"
fi

bookmark/read
http://rute.2038bug.com/index.html.gz
http://tldp.org/LDP/Bash-Beginners-G...tml/index.html
http://www.tldp.org/LDP/abs/html/

ravi_nandula · 03-27-2012, 11:38 PM

hi kbp,

ooh ok.
Thanks for helping.......Now I got it.

ravi_nandula · 03-27-2012, 11:44 PM

Hey,

I am having one more doubt.....regarding hidden files in linux.
If i go with "ls -a" I can see all the hidden files....my doubt is

1.who creates those hidden files
2.what data will be inside those hidden files.
----------------------------------

In my linux Redhat 6.2 server edition....if I go with "ls -a " I can see 2 hidden files with dark blue color....2 files are
1.single dot[.]
2.double dot[..]

So please explain me about the hidden files....

Thanks in advance.....

kbp · 03-27-2012, 11:56 PM

These represent the current directory (.) and the parent directory (..), if you try 'cd .' or cd ..' you'll see what I mean.

ravi_nandula · 03-27-2012, 11:58 PM

yah what you said is rite.

But when ever i create a DIR ...I can see 2 files created automatically......why those are created???

pan64 · 03-28-2012, 01:01 AM

. and .. are always created, those are by default "available", the system needs them to be able to walk in the directory tree.

ravi_nandula · 03-28-2012, 01:12 AM

hi pan,

Can I know what is directory tree???????

ravi_nandula · 03-28-2012, 01:49 AM

Hi everybody,

Trouble with scripting.......
Below is the script which I wrote but giving the error .i : COMMAND NOT FOUND IN LINE 5
------------------------------------------
i=5
while test $i != 0
do
echo "$i"
i=`expr $i - 1`
done
----------------------------------------
PLEASE HELP ME

pan64 · 03-28-2012, 03:00 AM

you have a root directory represented by a /. All of the subdirs inside are named as /dir1, /dir2, /dir_whatever.
All of these subdirs can have subdirs, like /dir1/subdir1 /dir5/subdir9 and so on. This structure can be represented as a tree - beginning from its root - so usually it is called directory tree. All of the available stuff in a linux can be found in a directory, somewhere in this directory tree.

This script is working (for me).

grail · 03-28-2012, 04:38 AM

I think you need to go back and look at your notes on testing strings and testing numbers in bash. May I also add, (()) is preferred over [[]] when doing arithmetic tests as standard
mathematical symbols may be used, ie. like <, >, etc

ravi_nandula · 03-28-2012, 04:42 AM

hey I need one more script
That will print the wishes like gud morning,eveng n night.....whenever system gets booted.......?
it should print automatically

TB0ne · 04-06-2012, 03:25 PM

Quote:

Originally Posted by ravi_nandula

hey I need one more script
That will print the wishes like gud morning,eveng n night.....whenever system gets booted.......?
it should print automatically

If you need a script, then WRITE IT YOURSELF. You've been pointed to bash scripting guides before, and can easily find lots more via Google. We'll be glad to HELP you, but you need to show some effort on your part. Post what you've written/done, and where you're stuck.

Otherwise, do your own work.