CODEWITHSUNDEEP
bashshelltruncate
peedee
peedee

Reputation: 2031

Unix shell script to truncate a large file

I am trying to write a Unix script which will truncate/empty a file which is continuously being written/open by an application when it reaches say 3GB of space. I know that the below command would do it : 

cp /dev/null [filename]

But I am going to run this in an production environment automatically as a cron job - just posting here to see if you guys faced any issues while doing something similar to this.

Upvotes: 100

Views: 66998

Answers (5)

Richard Buchmann
Richard Buchmann

Reputation: 31

There is an other alternative:

dd count=0 of=filename

The advantages (mainly useful for embedded systems):

  • It does not need to spawn shell (bash, dash etc.) because no redirection
  • Compatible to busybox

Upvotes: 0

Don Branson
Don Branson

Reputation: 13709

That seems reasonable to me. Unix, of course, would let you do this about 50 different ways. Here are two examples:

echo -n "" >filename
cat /dev/null >filename

Upvotes: 12

chepner
chepner

Reputation: 531065

Just to add another answer, 

: > filename

: is a no-op in bash (POSIX-compliant), so this essentially just opens the file for writing (which of course truncates the file) and then immediately closes it.

EDIT: as shellter commented, you don't actually need a command to go along with the redirection:

$ echo foo > foo.txt
$ cat foo.txt
foo
$ > foo.txt
$ cat foo.txt
$

A simple redirection all by itself will clear the file.

Upvotes: 133

San
San

Reputation: 4153

trunc filename

works on AIX flavor of UNIX

Upvotes: 3

Ricardo Marimon
Ricardo Marimon

Reputation: 10687

I've used the following command on debian 

truncate -s 0 filename

Upvotes: 72

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