Useful Commands For Unix Operating System

1.Deleting files older than N number of days ?

find . -name ‘*.trc’ -mtime +[N in days]  -exec rm {} \;  
Command will delete files older then N days in that directory

2.Copying file keeping timestamp preserve

cp -ip file.txt file_txt_bkp

3.Listing files modified in last N days

find . -mtime -<ndays> -exec ls -lt {} \;

4.Sorting files based on Size of file ? 

ls -l | sort -nrk 5  | more
du -sm *|sort -nr|head -10 

5.Finding CPU & Memory detail 

->cat /proc/cpuinfo  (CPU)
->cat /proc/meminfo (Memory)
->topas

6.Finding if any service is listening on particular port or not ?

netstat -an | grep {port no}  

7.Finding Process ID (PID) associated with any port ?

lsof | grep {port no.}  
lsof should be installed and in path.Many times it will be installed eith root user.Make sure you have that permission

9.Finding a pattern in some file in a directory ?

grep pattern  file_name  ( find pattern in particular file )
grep -i pattern  file_name (find pattern ignoring the case)

10.Create symbolic link to a file ?

ln -s  pointing_to_original_file  symbolic_link_name

example
 ln -s /home/text.txt test.txt

11.History of command executed in UNIX 

fc -l 
fc -e – ls ( Would execute the last ls command.) 
History command will also do the same
history

12. Compressing a big file

zip -r new.zip new
or
compress file_name

13.Creating a tar file

tar -cvwf file.tar file.txt

14.Extracting the files from a tar file

tar -xvwf myfile.tar(System would unarchive (untar) the myfile.tar file into the current directory.)
tar -xvwzf myfile.tar.gz(System would unarchive (untar) the myfile.tar.gz file in the current directory.)

14.Extracting a gz file?

Use guzip command as follows:
gunzip file.gz
OR
gzip -d file.gz

15.Extract a tar.gz or .tgz file?

Files with extension tar.gz or .tgz are tar files compressed with gzip. On Unix system extract them with following command:
gunzip < file.tar.gz | tar xvf –
gunzip < file.tgz | tar xvf –

If you have GNU tar (Linux system) you can use the z option directly:
tar xvzf file.tar.gz
tar xvzf file.tgz

16.Using mailx command

echo “This is going to be body of the mail” |mailx -s “Subject:Testing” “false@gmail.com”

17.Checking the file system free and used space

df -gt