1. When in doubt ..
    man commands

Samples: 
$ man talk
   $ man grep

2. What's my Unix system name, OS,CPU?
   $ uname -a

Sample result:

   SunOS hostname 5.8 Generic_108528-06 sun4u sparc SUNW, Ultra-5_10

3. Where am I (current working directory)?
   $ pwd
/export/home/user

4. Who am I?
   $ who           ; returns all users who logged on to the system.
$ who am i ; returns only your log in name and time.

5. What is my hostname?
   $ hostname

6. What is my account info?
   $ finger [account]    ; to see login name, real name, TTY, idle time, when & where

7. What is my default printer?
   $ lpstat -t    ; shows printer statistic and status

8. When pressing BackSpace it shows ^H, how do I set it to work correctly?
   $ stty erasectrl-v + bs ;press ctrl-v and back space button

9. Change directory
   $ cd /usr/bin
   $ cd ~+                  ; ~+ = cwd or "."   wherein ~- previous working directory
   $ cd $HOME         ; changes directory to your home folder = cd ~
   $ cd ../../hw1
$ cd ..                   ; moves one level up from your current working directory

10. List contents of the directory
   $ ls *[x,X]*        ; returns a listing of files that contain x or X in the file name
   $ ls -R               ; lists recursively that includes subdirectories 
   $ ls -li             ; displays long listing with inode number, or -a to list hidden files

11. File permissions
   $ chmod u+x, g-r myfileadd execute permission to user, remove read from group
   $ chmod u=rx, g=r, o=file   ; allows user to read and execute, group to read, no
                                                    read, write and execute for others
   $ chmod a=rxfile          ; allows user, group and others to read and execute
   $ chmod 754 myfile7-> 111 in binary represents rwx for user
                                             5-> 101 in binary represents r-x for group
                                             4-> 100 in binary represents r-- for others
12. Read text file(s)
   $ catmyfile                    ; alternately, you can use more myfile
   $ catmyfile news mail    ; read multiple files
   $ cat *ing

13. Copy file(s)
   $ cpmyfile newfile
$ cp * ../hw
   $ cp -r /home/mydir /home/newdir   ; copies everything in mydir to newdir
   $ cp -p source destination               ; retains existing permissions (copy ACL along)
   $ cp -i source destination                ; does not overwrite an existing file

14. Move files to another directory
   $ mv * /home/my_account
   $ mvmyfile $HOME

15. Delete file(s)
   $ rm myfile
$ rmmyfile?        ; removes myfile1, myfile2, myfile3 and so on.

16. Make a directory
   $ mkdirmydir

17. Delete an empty directory
   $ rmdirmydir

18. Delete a directory that contains files and subdirectories
   $ rm-rmydir       ; removes recursively all files and subdirectories

19. Symbolic link (can span/accross file systems)
   $ ln -sfile1link1   ; uses ls -li to see link1-> file1 with 2 different inodes.
                                  symbolic link always has a=rwx permissions

20. Hard link (files contain the same inode, can not span file systems)
   $ lnfile1 link1      ; allows the same file to be accessed under different names

Related:

• Introduction to UNIX

Unix Books :-
UNIX Programming, Certification, System Administration, Performance Tuning Reference Books

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