Shell command to truncate a file [solved]

[theYinYeti]

I forgot to stop a TV recording, which resulted in a giant file taking up all remaining free space on disk.

Now I want to keep only the first 12GB from this file.

 

The disk is so full I can't free 12GB on it, to be able to use the "head" command.

I know I can (and will) use something like "head --bytes=12000m FILE | ssh remoteuser@remotehost 'cat >TAIL-FILE'". But…

 

I'd like to know how I can truncate a file to its first bytes when neither the network nor extra disk space is available.

 

Yves.

Edited June 3, 2008 by theYinYeti

[ramfree17]

a quick search for linux and truncate revealed this links: http://linux.about.com/library/cmd/blcmdl2_truncate.htm

 

which according to pbone.net is either in the ltp package: http://rpm.pbone.net/index.php3/stat/4/idp...0.i386.rpm.html

 

or in the embutils package: http://rpm.pbone.net/index.php3/stat/4/idp...1.i586.rpm.html

 

based on the description it does not move the file so it seems like what you are looking for.

 

ciao!

Edited June 3, 2008 by ramfree17

[theYinYeti]

a quick search for linux and truncate revealed this links: http://linux.about.com/library/cmd/blcmdl2_truncate.htm

This is a C system call. I cannot use it directly.

 

which according to pbone.net is either in the ltp package: http://rpm.pbone.net/index.php3/stat/4/idp...0.i386.rpm.html

And those are just test cases for the kernel function that is called by the above system call.

 

or in the embutils package: http://rpm.pbone.net/index.php3/stat/4/idp...1.i586.rpm.html

 

based on the description it does not move the file so it seems like what you are looking for.

I didn't notice this one before. It may indeed be what I'm looking for, even though it's deep under /usr/lib… Thanks, I'll try.

 

Yves.

[theYinYeti]

Excellent! :) It works:

[yves@localhost ~]$ truncate 
usage: truncate size filename [filename...]
[yves@localhost ~]$ echo "hello hello" >testfile
[yves@localhost ~]$ echo "bye bye" >>testfile
[yves@localhost ~]$ ls -li testfile 
711918 -rw-r--r-- 1 yves yves 20 2008-06-03 10:27 testfile
[yves@localhost ~]$ cat testfile 
hello hello
bye bye
[yves@localhost ~]$ truncate 10 testfile 
[yves@localhost ~]$ ls -li testfile 
711918 -rw-r--r-- 1 yves yves 10 2008-06-03 10:27 testfile
[yves@localhost ~]$ cat testfile 
hello hell[yves@localhost ~]$

Thanks again.

 

Yves.

Edited June 3, 2008 by theYinYeti

[ramfree17]

cool! :)

 

ciao!

[Guest senyahnoj]

If you are using bash you can simply do:

 

> filename

 

not sure about other shells...

Edited October 23, 2008 by senyahnoj

[ramfree17]

If you are using bash you can simply do:

 

> filename

 

wouldnt that overwrite the whole file (aka redirection)? the original problem is to truncate a file up to a certain point so that the file contents is still usable and space is freed up.

 

ciao!