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Why do you not want to restore from backup?
Since Linux is multiuser and multitasking operating system other users/process can overwrite deleted file disk space. There is no guarantee that any particular file will be able to be undeleted. If desired you can create a backup of the partition dd bs=4M if=/dev/partition of=partition.backup as a precautionary measure to save the deleted file from being overwritten. As explained in the link below if oracle is still has the data file opened it might be possible to recover like:
Will output something like this:
progname 5559 user 22r REG 8,5 1282410 1294349 /path/to/file
Take the 2nd column 5559 and fouth number 22 and use the copy command:
cp /proc/5559/fd/22 restored.file
I recommend photorec and testdisk.
And lots more information can be found by searching the web.