[SOLVED] Help With shell script

pubudumj · 04-02-2012, 11:44 AM

#!/bin/bash

tar -cvf /dev/st0 /www /home 2>/dev/null

[ $? -eq 0 ] && status="Success!" || status="Failed!!!"

mail -s 'Backup status' vivek@nixcraft.co.in<<END_OF_EMAIL

The backup job finished.

End date: $(date)
Hostname : $(hostname)
Status : $status

END_OF_EMAIL

Could someone please explain me this script line by line?

Sydney · 04-02-2012, 11:57 AM

I can try no warranty

Quote:

Originally Posted by pubudumj

#!/bin/bash

tar -cvf /dev/st0 /www /home 2>/dev/null # tar up the file to /home

[ $? -eq 0 ] && status="Success!" || status="Failed!!!" # if tar is not an error code of 1 set status to Success else Failed

mail -s 'Backup status' vivek@nixcraft.co.in<<END_OF_EMAIL # Send me an email

The backup job finished.

End date: $(date) # run the date command
Hostname : $(hostname) # run the hostname command
Status : $status # print status from line above

END_OF_EMAIL

Could someone please explain me this script line by line?

Email should look like this:

Code:

The backup job finished.

Mon Apr 2 11:58:20 CDT 2012
MYHOST.MYDOMAIN
Success!

pubudumj · 04-02-2012, 12:04 PM

Thanks mate for your kind reply...

Actually i want to know about this line,..

[ $? -eq 0 ] && status="Success!" || status="Failed!!!"

Sydney · 04-02-2012, 12:14 PM

Quote:

Originally Posted by pubudumj

Thanks mate for your kind reply...

Actually i want to know about this line,..

[ $? -eq 0 ] && status="Success!" || status="Failed!!!"

if you go to the terminal and run a command that gives you an error message and then

Code:

echo $?

it will return a 1. If the last command was successful is till return a 0. -eq is an evaluation for equals then you have the results if true the first thing || (or) is false the second

pubudumj · 04-02-2012, 12:27 PM

Quote:

Originally Posted by Sydney

if you go to the terminal and run a command that gives you an error message and then

Code:

echo $?

it will return a 1. If the last command was successful is till return a 0. -eq is an evaluation for equals then you have the results if true the first thing || (or) is false the second

Thanks sydney...Thank you very much..Very clear description.I understood them all

Thanks again

Sydney · 04-02-2012, 12:29 PM

Quote:

Originally Posted by pubudumj

Thanks sydney...Thank you very much..Very clear description.I understood them all

Thanks again

LOL is till should be it will, sorry, but I am happy you found it clear.

pubudumj · 04-02-2012, 12:32 PM

Quote:

Originally Posted by Sydney

LOL is till should be it will, sorry, but I am happy you found it clear.

Hey sydney im new to Linux..And im going to do RHCSA in this month..I think you are a person that have a good linux knowledge. Can i found you on Fb or twitter? Or your mail address?

Sydney · 04-02-2012, 12:35 PM

I have accepted your friends request. I have been studying for that test for a while and work with Red Hat every day. If you are new to Linux I would suggest either their classes or a ton of time on systems. I would be happy to help you, but this forum is probably your best bet on ways to find out stuff that is puzzling.

pubudumj · 04-02-2012, 12:37 PM

yeah Sydney,,anyway thanks for all the help..will meet again.Thanks again friend.Have a nice day

abarclay · 04-02-2012, 02:21 PM

Just a couple of comments.

The line below doesn't backup the file to /home, it actually backs up both /www and /home to the tape drive. The stuff in /dev usually represent devices on the system. "st" means "Scsi Tape". The 0 means the first scsi tape.

Code:

tar -cvf /dev/st0 /www /home 2>/dev/null

The following line is, quite frankly, a mess. Why someone would write something convoluted like this, I'll never know.

Code:

[ $? -eq 0 ] && status="Success!" || status="Failed!!!"

Here it is, rewritten to be more clear.

Code:

returnCode=$?
if [ $returnCode -eq 0 ]
then
     status="Success!"
else
     status="Failed!"
fi

Code:

mail -s 'Backup status' vivek@nixcraft.co.in<<END_OF_EMAIL

The line above invokes the mail system to send email to vivek@nixcraft.co.in with subject line 'Backup status'.
Normally, the mail system will read the contents of the email from stdin (the keyboard). If you wanted to email he contents of a file (/tmp/mailbody.txt), you could have used this:

Code:

mail -s 'Backup status' vivek@nixcraft.co.in </tmp/mailbody.txt

The "<<" is a special item called a "here document". It means, "I want you to redirect the input of this command from a file - Oh, and by the way, here is the content of the file."
The "END_OF_MAIL" is just a string that defines the start and end of the 'file' contents to be redirected into the command.
This is very useful as it obviates the need to create an intermediate file.

Sydney · 04-02-2012, 02:27 PM

Quote:

Originally Posted by abarclay

Just a couple of comments.

# The line below doesn't backup the file to /home, it actually backs up both /www and /home to the tape drive. The stuff in /dev usually represent devices on the system. "st" means "Scsi Tape". The 0 means the first scsi tape.
tar -cvf /dev/st0 /www /home 2>/dev/null

[ $? -eq 0 ] && status="Success!" || status="Failed!!!"
# the line above is, quite frankly, a mess. Why someone would write something convoluted like this, I'll never know.
# Here it is, rewritten to be more clear.

Code:

returnCode=$?
if [ $returnCode -eq 0 ]
then
     status="Success!"
else
     status="Failed!"
fi

mail -s 'Backup status' vivek@nixcraft.co.in<<END_OF_EMAIL
# the line above invokes the mail system to send email to vivek@nixcraft.co.in with subject line 'Backup status'.
# Normally, the mail system will read the contents of the email from stdin (the keyboard). If you wanted to email
# the contents of a file (/tmp/mailbody.txt), you could have used this:
mail -s 'Backup status' vivek@nixcraft.co.in </tmp/mailbody.txt

# The "<<" is a special item called a "here document". It means, "I want you to redirect the input of this command from a file.
# Oh, and by the way, here is the content of the file."
# The "END_OF_MAIL" is just a string that defines the start and end of the 'file' contents to be redirected into the command.
# This is very useful as it obviates the need to create an intermediate file.

Yep, I totally glazed over the dev path in that line. This is a much better explanation. Thanks,

pubudumj · 04-02-2012, 10:50 PM

Quote:

Originally Posted by abarclay

Just a couple of comments.

The line below doesn't backup the file to /home, it actually backs up both /www and /home to the tape drive. The stuff in /dev usually represent devices on the system. "st" means "Scsi Tape". The 0 means the first scsi tape.

Code:

tar -cvf /dev/st0 /www /home 2>/dev/null

The following line is, quite frankly, a mess. Why someone would write something convoluted like this, I'll never know.

Code:

[ $? -eq 0 ] && status="Success!" || status="Failed!!!"

Here it is, rewritten to be more clear.

Code:

returnCode=$?
if [ $returnCode -eq 0 ]
then
     status="Success!"
else
     status="Failed!"
fi

Code:

mail -s 'Backup status' vivek@nixcraft.co.in<<END_OF_EMAIL

The line above invokes the mail system to send email to vivek@nixcraft.co.in with subject line 'Backup status'.
Normally, the mail system will read the contents of the email from stdin (the keyboard). If you wanted to email he contents of a file (/tmp/mailbody.txt), you could have used this:

Code:

mail -s 'Backup status' vivek@nixcraft.co.in </tmp/mailbody.txt

The "<<" is a special item called a "here document". It means, "I want you to redirect the input of this command from a file - Oh, and by the way, here is the content of the file."
The "END_OF_MAIL" is just a string that defines the start and end of the 'file' contents to be redirected into the command.
This is very useful as it obviates the need to create an intermediate file.

Wow what a nice explanation...THanks alot mate.Anyway could you please explain me this little thing?

2>/dev/null

chrism01 · 04-03-2012, 12:06 AM

Code:

2>/dev/null

means send channel 2 ie stderr to virtual device /dev/null; essentially it s a blackhole ie you're just throwing away/ignoring any error msgs