cd                   to change directory
                
cd -                 to go back to the previous directory
                
cd ..                to go to the parent directory
                
cd ./                using relative pathname ( "./" is the current directory)

                
pwd                  to print working directory (shows where you are)

                
ls                   to list the files
                
ls /*                to list the files in another directory
                
ls -l                long format
                
ls -lt               long format + sort results by the file's modification time
                
ls -lt --reverse     like ls -lt but in reverse
                
ls -a --all          lists all files, even hidden
                
ls -A --almost all   like -a except . and .. (current directory and parent directory)
                
ls -d --directory    to see detail about directory (not the content)
                
ls -F --classify     appends an indicator at the end of name
                
ls -h --human-readable  display size in human readable format
                
ls -r --reverse      display result in reverse order (instead of alphabetical)
                
ls -s                sort results by file size
                
ls -t                sort by modification time
                
ls -li               show inode for hard links

                
file "filename"      file description
                
less "filename"      examine textfile
                
     /characters     search forward for "characters"
                
     n               search for the next occurence of previous search
                
     h               display help screen
                
     G               move to the end of the text file
                
     g               move to beginning

                
cp                   copy files and directories
                
    -a               also copy attributes, like ownerships and permissions
                
    -i               prompt before overwritting existing file
                
    -r               recursively copy directories and their contents
                
    -u               updates files or copy files that dont exist already
                
    -v               verbose, displays information while copying

                
mv                   move/rename files and directories
                
    -i               prompts before overwriting an exising file
                
    -u               updates files
                
    -v               verbose, displays information

                
mkdir                create directories
                
     mkdir dir1 dir2 dir3
                
rmdir                delete directories
                
     rmdir dir1 dir2 dir3
                
rm                   remove files and directories (trick: use ls first)
                
    -i               prompts for confirmation
                
    -r               recursive, every directories in it
                
    -f               force
                
    -v               verbose, displays information

                
ln       Create hard and symbolic links
                
    -s   symbolic link (ex: ln -s fun fun-sym  /or/  ln -s ../fun dir1/fun-sym)

                
Wildcards :
                
*               Matches any characters 
                
?               Matches any single character 
                
[characters]    Matches any character that is a member of the set characters
                
[!characters]   Matches any character that is not a member of the set characters
                
[[:class:]]     Matches any character that is a member of the special class
                
    [:alnum:]   alphanumeric character
                
    [:alpha:]   alphabetic character
                
    [:digit:]   numeral
                
    [:lower:]   lowercase letter
                
    [:upper:]   uppercase letter