Hi Friends and Gurus,

I want to edit a crontab file with the help echo command.

we are using a tool called HP Opsware
opsware is a GUI tool which connects to UNIX servers with root permissions.

here my query is just assume i have a file called test.txt
here i want to comment the 9th line, i mean put a hash on 9th line with the help of echo command.


host1#cat -n test
cat -n test
1 This is a test file
2 This is a test file
3 This is a test file
4 This is a test file
5 This is a test file
6 This is a test guava
7 This is a test apple
8 This is a test mango
9 This is a test orange
10 This is a test anar.


any help is appreciated....


Thanks & Regards
JNReddy

Why do you want to do it with echo when sed is ideally suited to the task?

hi Catkin

Thank you for your reply i dont know how to use the sed.can you please provide me command to fullfill my task.

Thanks & Regards
JNReddy

Hi,

Assuming you know which line you need to comment out (line 9 in your example: The 9 tells sed which line to work on. The s/^/#/ tells sed to (re)place a # at the beginning (the ^) of the line.

After you check if this is correct use sed's -i option to chance the infile:Also have a look here: GNU sed, a stream editor and USEFUL ONE-LINE SCRIPTS FOR SED

Hope this helps.

1 members found this post helpful.

You will learn much more by looking at the references offered (at the end) than the answer.

I can able to comment the 9th line, but its not making changes in the original file

$sed '9s/^/#/' test
This is a test apple
This is a test banana
This is a test orange
This is a test apple
This is a test apple
This is a test apple
This is a test apple
This is a test apple
#This is a test apple
This is a test apple

orly$cat test
This is a test apple
This is a test banana
This is a test orange
This is a test apple
This is a test apple
This is a test apple
This is a test apple
This is a test apple
This is a test apple
This is a test apple

I redirected the output to another file, it would be great if it make changes to original file..sed '9s/^/#/' test > test1
orly$sed '9s/^/#/' test > test1
1 This is a test apple
2 This is a test banana
3 This is a test orange
4 This is a test apple
5 This is a test apple
6 This is a test apple
7 This is a test apple
8 This is a test apple
9 #This is a test apple
10 This is a test apple


Thanks & Regards
JNReddy

Hi,
That is why I included the comment about using the -i option....

For the record, the vast majority of command line tools are unable to alter the original input, and only print the modified results to stdout. You must use a temporary file in most cases.

Even the -i option above is just an extension added to the gnu version of sed, and not available in other implementations. And all it does is use a temporary file in the background anyway.


If you really want to do script-based direct editing of files, check out ed.

http://wiki.bash-hackers.org/doku.php?id=howto:edit-ed

There is nothing wrong in using the mighty vi to edit a file

$ echo ":9^Mi#^[ZZ" | vi file.txt

This edit file file.txt and add a # to the beginning of line 9 every time it's run.

Note that ^M is typed as [CTRL-V ENTER] and ^[ as [CTRL-V ESQ]