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CUT command problem

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# 1  
Old 03-25-2011
CUT command problem
Hi

I have a strange problem when using cut command

when i am using the below command, it is working fine,I am getting the data in new file xyz.dat
Code:
cut -c 1-75 abc.dat > xyz.dat

when i am using the below command, I am getting the data in new file abc.dat , but empty file
Code:
cut -c 1-75 abc.dat > abc.dat

could you help me out

Thanks in advance
Last edited by Franklin52; 03-25-2011 at 09:42 AM.. Reason: Please use code tags
# 2  
Old 03-25-2011
Code:
cut -c 1-75 abc.dat > tmp.dat
cat tmp.dat >abc.dat
rm tmp.dat

# 3  
Old 03-29-2011
Quote:
Originally Posted by vaas
Hi

I have a strange problem when using cut command

when i am using the below command, it is working fine,I am getting the data in new file xyz.dat
Code:
cut -c 1-75 abc.dat > xyz.dat

when i am using the below command, I am getting the data in new file abc.dat , but empty file
Code:
cut -c 1-75 abc.dat > abc.dat

could you help me out

Thanks in advance
The redirection (> abc.dat) is set up by the shell well before the cut program is executed. This replaces abc.dat with an empty file which cut then opens for input also.

You need to do something like
Code:
cut -c 1-75 abc.dat > abc.dat.tmp
mv -f abc.dat.tmp abc.dat

The nice thing about using mv instead of copy is that mv, if interrupted, guarantees to leave the original file intact.
# 4  
Old 03-29-2011
Thanks a lot...it was very useful for the beginner like meSmilie

thanks once again
# 5  
Old 03-29-2011
Quote:
Originally Posted by DoxieLvr
Code:
cut -c 1-75 abc.dat > abc.dat.tmp
mv -f abc.dat.tmp abc.dat

The nice thing about using mv instead of copy is that mv, if interrupted, guarantees to leave the original file intact.
Yes but the inode of the target file will be lost.
using
Code:
cat abc.dat.tmp >abc.dat

and then
Code:
rm abc.dat.tmp

instead of
Code:
mv -f abc.dat.tmp abc.dat

will preserve it.

So all depends on what behaviour the user does expect.
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