1. List recently touched files -  $ls -alt

2. List recently changed files -  $ls -alc |tail

3. Delete unchanged/obsolete arch files older than 5 days  - $find $ORACLE_BASE/arch/arch*.arc -ctime +5  -exec rm {} \;

4. Display file sizes in 512-byte blocks - $du -s * |sort -n|tail or $du -sh * |sort -n|tail

5. Locate files that contains certain strings - $find . -print|xargs grep -i v\$session

6. Find recently created files - $find . -mtime -1 -print (displays files created during the past day)

7. Find files with very large size - $find . -size +50000 -print (displays all files greater than 50000 bytes)

8. Delete files older than a week or certain period. - $find . -mtime +7 -exec rm {}  \; (remove all files more than 7 days old)

9. Delete old trace,log,dump,audit files-  Same as above except you need to start from ADR home.
$find /u01/app/oracle/diag/rdbms/testdb/DB11G/ -name "*.trc" -mtime +7 -exec rm {}  \;

10. Allocate an empty files - $touch test.txt

11.Change default file permissions - $umask 644

12. Change file ownership - $chown oracle:oinstall *.dmp

13.Change file permissions - $chmod 755 *.sql

14. Tar and UNTAR files -$tar -cvf new.tar *.sql (TAR) $tar -xvf new.tar (UNTAR)

15. SCP files from one server to another server - $ scp *.dmp user@host_name:/backup/. (push) $scl user@host_name:/backup/*.dmp /backup/. (pull) . To copy a directory, use the -r (recursive) option. Example: $scp -r mydir xyz@sdcc7:mydir

16. gzip and gunzip files: $gzip *.dmp $gunzip *.zip

17. WINSCP - Copy files from windows to Unix and vice versa.

18. umask  $umask 755