manview the online documentationman cdThe manual pages for the cd command are displayed at your terminal.
cat / more / lesslist a file on standard output (default standard output is the terminal)cat .bashrcThe contents of the .bashrc file are displayed. cat displays the whole file at once, whereas more and less display a screen at a time.
head   list the beginning of a file on standard outputhead -50 myfileThe first 50 lines of "myfile" are displayed.
tail   list the end of a file on standard outputtail -70 myfileThe last 70 lines of "myfile" are displayed.
cp   copy a filecp oldfile newfileA copy of "oldfile" is made, and saved as "newfile".
mv   move a filemv oldfile newfileThe file "oldfile" is moved (renamed) to a file called "newfile".
rm   remove / delete a filerm tempfileRemove (delete) the file called temp.
ls   list the contents of a directoryls mydirLists the contents for the "mydir" directory.  If the directory name is omitted, current directory is assumed. 
chmodchange the access permissions of a file  chmod ugo+rwx fileAllow owner, group and others read, write and execute permission for file.
pwd   print working directorypwdGives the full pathname of the directory in which you are currently working.
cd   change directorycd subdirChange to a "subdir" directory as specified.
mkdir   make / create a new directorymkdir subdirCreates a directory called subdir as a subdirectory of your current directory.
rmdir   remove / delete a directoryrmdir subdirRemoves subdir, only if it is empty (contains no files).
vi   invoke the vi (vim) editorvi newfileEdit the file newfile. If newfile does not exist, an empty file is opened for editing.
diff   compare two files and show the differencesdiff file1 file2Compares file1 with file2.
grep   search for a regular expression in a filegrep error file1Prints out every line of the file "file1" which contains the string "error". Additionally, you can also use wildcards in the search pattern.
kill terminate a process which is owned by youkill 1234Terminate the process with process id 1234 .