At 2005-01-13T12:12:19+1300, Rik Tindall wrote:
> - probably better to have been running this: sed -e 's/few/two/' <
> sedsort.txt > sedsort.txt
Only if you want to turn sedsort.txt into an empty file...
> [EMAIL PROTECTED] rik $ sed -e 's/figner/finger/' -e 's/few/two/' <
> sedsort.txt
> > sedsort.txt
> [EMAIL PROTECTED] rik $ cat sedsort.txt
> [is now empty :-/]
...as you've just discovered.
The reason this happens is that the shell opens the files for
redirection before executing the new process (sed, in this case). The
'>' redirection is telling the shell to create a new file, or truncate
an existing one, and begin writing to the start of the file. By the
time the sed process runs, it's going to be reading input from an empty
file and writing it's output (none) to the same empty file.
Assuming you're using a Bourne-like shell (I'd guess you're using bash),
you can avoid this by enabling the 'noclobber' shell option, i.e. 'set
-o noclobber'.
Cheers,
-mjg
--
Matthew Gregan |/
/| [EMAIL PROTECTED]
