This program models a file recovery logic, It looks difficult. But its logic is very easy. We write code to recover a file in a seperate file, bundle.sh. Then execute bundle.sh to get back what was deleted. see how it works. I've tried my best to put what i know into words. Hope you get it.
if [ $# -eq 0 ]
then
echo "No arguments passed"
exit 1
fi
if no command line arguments are passed (names of files to be backed up are expected actually), we print appropriate message and exit. fi represents end of if.
for i in $*
do
for each command line argument(name of file) we should back up its "Name+Shell code to recovery it+The contents to recover after restoring file".
we do it for each file using for loop.
$* represents total number of files, for each 'i' in $* means for each file, we write its code to recover.
echo "echo "code to recreate the file $i ""
This will produce a output as echo "code to recreate the file $i " (content in bold letters), on the output screen actually. But since we are redirecting output to a bundle.sh file, echo "code to recreate the file $i " this line will be printed in bundle.sh file.
echo "cat>$i<<endf"
cat $i
echo "endf"
this line prints cat>$i<<endf to bundle.sh. which is nothing but (cat>fiilename and hitting enter button on your keyboard).
remember we can write contents to file using cat>filename, and end writing contents by clicking ctrl+d. same this done here. but code to do so is pasted in bundle.sh so that when we execute the bundle.sh, we can restore contents of file.
after cat>i is written to bundle.sh, we need to feed the input to be stored in that i file.
this is done using "cat $i" . This writes contents of i file to bundle.sh.
'endf' here serves as ctrl+d to indicate end of file.
So what we did here was, typing cat>filename and hitting enter (endf which is nothing but \n) on terminal, writing contents of file. and indicating end of input to file by ctrl+d.
echo "echo" Creation done " "
This prints the following to bundle.sh, echo" Creation done ".
done
exit 0
done indicates end of loop body.
----------------------------------------------------------------------------
BUNDLE.SH:
So basically what we have now bundle.sh is now this,
echo "code to recreate the file $
cat>$i<<endf
<content of i'th file written using cat $i above>
endf
which is nothing but code to write a content to a file with a name equal to content of $i.
When we execute this bundle.sh in shell, we will get back what was deleted. Isn't it? :p
Remember
executing this code is done by this command,
sh 9a.sh a.txt b.txt>bundle.sh
Cool. Done. Sit back and grab your pop corn now.
Share your views about this article!