elementary shell and sftp

You need to be a Power User!

version 0.1
August 2011
author: smh

If you understand the console-based commands for invoking or controlling applications, you have a POWERFUL advantage over those who are limited by knowing only GUI-based control. When you know what's really going on, then you are more easily able to ramp up your knowledge when confronted with a new GUI interface that simplifies (i.e., "dumbs down") interaction to an application you already know.

To that end, we have here a golden opportunity to learn some console-based shell commands (the shell is the part of an operating system that interacts with a user) and some sftp commands.

Keep in mind, a GUI interface interprets your mouse clicks into something rather like shell commands, then those commands are executed. It may look like the mouse click does something directly -- but that would be wrong.

Files, Directories, Paths: Review of file structure and navigating the structure
Open a shell and table of shell commands: Basic shell commands for OS X and Windows
Open an sftp connection and table of sftp commands: Invoking and using sftp
Self-Test

If, after this little paper, you feel you need more work in this area, there are a huge number of tutorials on the Web and there are a myriad of technical books. Get yourself comfortable and look them up.

Files, Directories, Paths

The file system is organized into a tree-like structure. At the top of the the file system is the root directory. All files and directories in the file system can be reached from the root directory. A directory can "hold" from zero to many directories and zero to many files. A file cannot "hold" anything (in the file structure).

From a specific directory or file looking "up" there is one path to the root. From a specific data file looking "down", there is no where else to go -- a file cannot "hold" anything in the file structure. From a specific directory looking down, there are from 0 to many possible branches.

A picture may help here. insert picture of approximately:

/
	Stuff/
		HisStuff/
			f1.txt
			Pictures/
				p1.jpg
				p2.jpg
			f2.txt
		MyStuff/
			file1.txt
			file2.txt
			/Projects
				P1/
					p1.java
					p1.class
				P2/
					p2a.java

Speaking casually, we say a directory contains directories and files, and a file contains data.

A directory or a file is identified in the file system by its path. A complete path for a directory or file is the complete specification of all directories from the root to the desired destination. A relative path is the specification of directories to a desired destination but starting at a location different from the root. The path to the desired file (directory) relative to a specific starting directory.

There are two special names used in the file system. '.' refers to the current working directory. '..' refers to the working directory's parent.

Complete path examples

Using the picture already given, the complete path for the file file1.txt is /Stuff/MyStuff/file1.txt. The complete path for the directory named P1 is /Stuff/MyStuff/P1.

Relative path examples

Using the picture already given, if the current working directory is P1 (e.g., pretend you're editing p1.java), then the relative path to Projects is .., and the relative path to P2 is ../P2. If the current working directory is P1, then the relative path to f1.txt is ../../../HisStuff/f1.txt.

Open a shell

OS X	OS X flags	Win	Win flags	action
man cmd				on line documentation of shell command cmd
ls	-l give more information	dir	/w wide output format	list contents of current directory
ls path	-l	dir path		list contents of path
pwd				print path of current working directory
cp f1 f2		copy f1 f2		create a copy of file f1 and place in file f2
mv f1 path				move file f1 to location given by path
cd path				change working directory to path
pwd				print (on screen) path of working directory
rm f1		del f1		delete file f1
mkdir d1				create a new directory named d1 in current working directory
rmdir d1				delete directory named d1
vi f1		edit f1		open plain text editor on file f1
sftp username@hostname				open sftp client to host hostname using user username
ssh username@hostname				open ssh connection to host hostname using user username

Open an sftp connection

Type sftp username@hostname to invoke an sftp client. The client will open an sftp connection to the sftp server that is running on the host machine named hostname.

Your machine (running the sftp client for you) is the local computer. The machine running the sftp server for you (at hostname) is the remote computer. The local computer uploads data to the remote computer and downloads data from the remote computer.

A table of useful sftp commands

command	action
?	print a list of ftp commands
put f1	uploads file f1 in local working directory to remote working directory
get f1	download file f1 to local working directory from remote working directory
mkdir d1	create new directory in remote working directory
pwd	print path of remote working directory
cd path	change remote working directory
ls	print contents of remote working directory
lpwd	print path of local working directory
lcd path	change local working directory to path
lls	print contents of local working directory
bye	end sftp connection and close sftp client

A small gotcha

If you are sftp-ing to people.emich.edu, access permissions on files you upload are automatically set properly (read and execute for directories, and read for files) because people.emich.edu is configured to serve as a web server for EMU people. However, if you are trying to set up a website on another, perhaps more general purpose machine, then you may have to set access permissions yourself.

Setting access permission with sftp is not as intuitive as setting them with a shell. The same command chmod is used, but sftp requires numeric arguments rather than symbolic. To give read access to index.html for all users, use
chmod 644 index.html
To give read and execute access to directory Dir1 for all users (you need both read and execute to get the behavior you probably want) use
chmod 755 Dir1