Bash – How to periodically remove all content from a file without deleting it

bashcronscripting

I need to periodically empty a text file without deleting it (I know how many lines it has).

I tried this:

Created a cron that executes the following script

other lines from the script here

sed '1,14d' file.txt>file.txt

If I run it from a terminal it works fine, but when I run the cron it executes the first part (the "other lines from script here" part) but it doesn't empty the file.

Note: The file has 777 permissions so I don't think it's permissions related.

Best Answer

Maybe the current working directory isn't what you're expecting when cron executes the script. Try specifying the full path to file.txt. Also, this should empty the file as well, just in case there's some issue with the sed command:

echo > file.txt

Related Solutions

Cron – 403 forbidden error from cron

Your webserver is not configured to allow access to the file you are trying to download. You need to solve that first before you attempt to run this download from cron.

First, figure out how your webserver is configured. If you are using apache you should be able to find /etc/apache/httpd.conf or /etc/apache2/httpd.conf or similar. That file should point you towards how your webserver is set up.

Second, check your error log. That should be something like /var/log/apache/error.log. That file should provide additional info on why the wget is failing.

Debug that problem. Once you get the wget working you can try running it in cron.

Also you could try using curl instead of wget. Something like this:

curl -s http://www.mydomain.com/test.php >/dev/null

should work fine too. I don't have a strong reason to prefer wget or curl in this case.

Bash – How to output a list of changed files from rsync

You can use rsync's --itemize-changes (-i) option to generate a parsable output that looks like this:

~ $ rsync src/ dest/ -ai
.d..t.... ./
>f+++++++ newfile
>f..t.... oldfile

~ $ echo 'new stuff' > src/newfile

~ $ !rsync
rsync src/ dest/ -ai
>f.st.... newfile

The > character in the first position indicates a file was updated, the remaining characters indicate why, for example here s and t indicate that the file size and timestamp changed.

A quick and dirty way to get the file list might be:

rsync -ai src/ dest/ | egrep '^>'

Obviously more advanced parsing could produce cleaner output :-)

I came across this great link while trying to find out when --itemize-changes was introduced, very useful:

http://andreafrancia.it/2010/03/understanding-the-output-of-rsync-itemize-changes.html (archived link)

Best Answer

Related Solutions

Cron – 403 forbidden error from cron

Bash – How to output a list of changed files from rsync

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