Help on Command.
man <cmd> 
Type man ls to read the manual for the ls command 
Navigate between Directories
ls -ltrah <path>
List contents of the directory <path> including entries starting with `.` in the long listing format with human readable size like 2G rather than

2146858929 and sorted by their modification date, oldest first.

cd <path>

Change the current directory to <path>

Show the absolute path of the current directory
Special Directories
Home directory
Current directory

Parent directory

Modify  Directories
mkdir -p <path> 
Make a new directory with the path <path>. Missing parent directories along the path will be created.
cp <file> <dst> 
Copy the file <file> to  the destination <dst>. If <dst> is a directory, the new file will be created inside it.
cp -r <dir1> <dir2> 
Copy directory dir1 and all its contents recursively as/to <dir2>. If <dir2> exists, the new directory will be created inside <dir2>.
mv <file> <dst> 
Move the file <file> to the destination <dst>. If <dst> is a directory, the file will be moved inside it.
rm <file>
Remove files. “?” is any character; “*” is any string of characters. 
rm -rf <dir>
USE WITH CAUTION. Remove all contents of the directory <dir> recursively and forcefully. 
Connect/Copy files to remote host
ssh <user> 
Login to Gadi as the user <user>
scp <file> <user><dst> 
Copy local <file> to Gadi into the directory <dst> or as the file <dst> 
View/Edit a Text File
less <file> 
View <file> with less 
cat <file> 
Print <file> on screen
vim <file> 
Edit <file> with vim 
emacs <file> 
Edit <file> with emacs 
Compress files
tar czf file.tar.gz <folder> 
Create the compressed archive <file.tar.gz> with gzip for all contents in the folder <folder> (use xzf to extract) 
gzip <file> 
Compresses file and renames it to file.gz 
Other Useful Commands
diff -y <file1> <file2> 
Show the differences between <file1> and <file2> side-by-side 
grep -n "str" <file> 
Print lines containing the string str in <file> with the prefix of its line number 
awk -F, '{print $4}' <file> 
Print the 4th column of the file <file> using comma as the field separator 
wc -l <file> 
Count lines in the file <file> 
find <path> -type d -name *1234*
Search through the directory <path> for directories with name containing the string 1234
File Access Permissions
chmod g+w <file>
Add group writable permission to the file <file>
chgrp -R <prj> <path>
Set the owner group of the directory <path> and its contents to the project <prj> recursively.
getfacl <file>
Get file access control lists of the file <file>
Pipes and Redirection
ls -l > list.txt 
List the content of the current directory and redirect the output to the file list.txt. If file list.txt exists, overwrite it with the output.
<cmd> >> <file> 
Append output of the command <cmd> to the file <file>
<cmd> < <file> 
Get input of the command <cmd> from the file <file>
<cmd1> | <cmd2> 
Pipe the output of command <cmd1> to the standard input of command <cmd2>
Halt the current command
Move cursor to the beginning of the line
Move cursor to the end of the line

Delete from cursor to the end of the line

Stop the foreground job and places it in the background as a stopped job
Log out of current session, similar to exit