Solved

How to Empty a File in a bash Shell Script

Posted on 2010-11-15
7
699 Views
Last Modified: 2012-05-10
The code is inside a loop that redirects output to a file. That file is then tested for whether it's empty or not. So, at the beginning of each iteration of the loop, I want to empty the file.

Can you tell me how to do that?

Something like this would be nice:

   FILE="$path/fileName"
   for ... do
      $FILE < EOF
      Other stuff...
      command 2> $FILE
      if $FILE not empty
          do something
      fi
   done
0
Comment
Question by:WizeOwl
7 Comments
 
LVL 26

Accepted Solution

by:
wilcoxon earned 350 total points
Comment Utility
To empty a file, you can just do:

cp /dev/null $FILE
0
 
LVL 5

Assisted Solution

by:sandipshah
sandipshah earned 50 total points
Comment Utility
Or delete the file and re-open it with the same name.

Ss
0
 
LVL 11

Assisted Solution

by:tel2
tel2 earned 100 total points
Comment Utility
Or simply:

    >$FILE
0
What Is Threat Intelligence?

Threat intelligence is often discussed, but rarely understood. Starting with a precise definition, along with clear business goals, is essential.

 
LVL 84

Expert Comment

by:ozo
Comment Utility
command 2> $FILE
will empty the file before it writes
0
 

Author Comment

by:WizeOwl
Comment Utility
Thanks for all the suggestions.

1) cp /dev/null $FILE   >> is probably closest to what I was looking for.
2) Brute force is to delete and let first redirect "2>" create it when needed, again.
3) If ">$FILE" works, that may be most elegant.
4) command 2> $FILE doesn't help when testing loop iterations.
0
 
LVL 84

Expert Comment

by:ozo
Comment Utility
command 2> $FILE doesn't help when testing loop iterations.
what are you testing that it doesn't help?
0
 

Author Closing Comment

by:WizeOwl
Comment Utility
>$FILE does work
0

Featured Post

How your wiki can always stay up-to-date

Quip doubles as a “living” wiki and a project management tool that evolves with your organization. As you finish projects in Quip, the work remains, easily accessible to all team members, new and old.
- Increase transparency
- Onboard new hires faster
- Access from mobile/offline

Join & Write a Comment

Suggested Solutions

The following is a collection of cases for strange behaviour when using advanced techniques in DOS batch files. You should have some basic experience in batch "programming", as I'm assuming some knowledge and not further explain the basics. For some…
In the distant past (last year) I hacked together a little toy that would allow a couple of Manager types to query, preview, and extract data from a number of MongoDB instances, to their tool of choice: Excel (http://dilbert.com/strips/comic/2007-08…
Learn several ways to interact with files and get file information from the bash shell. ls lists the contents of a directory: Using the -a flag displays hidden files: Using the -l flag formats the output in a long list: The file command gives us mor…
Explain concepts important to validation of email addresses with regular expressions. Applies to most languages/tools that uses regular expressions. Consider email address RFCs: Look at HTML5 form input element (with type=email) regex pattern: T…

771 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

12 Experts available now in Live!

Get 1:1 Help Now