This is a very short and superficial list of some of the core Unix
commands.  You can get the full story with the "man" command:

   man pwd
   man cp
   man man
   etc.

though its results are often too voluminous and complete for
newcomers.  (The original Unix man pages were typically only one
page each; things are not necessarily better these days.)

Suggestion: start editing this file to add your own discoveries
to it.  You need to learn some text editor; Word will not do.
TextEdit on a Mac is fine if you set it to produce plain text.
Pico and Nano are easy and already do the right thing.



BASIC COMMANDS

pwd	print working directory
	where am I in the file system

cd dir	change directory to dir
	   which is either relative to where you are or
	   a full path from the root / of the file system

	. is the current directory
	.. is the parent directory

cd .. 	will eventually take you to the root of the file system

cd	back to your home directory from anywhere

ls	list names of files in a directory (by default the one you're in)

ls -l	"long" -- give more information: size, permissions,
	      time of last change, ...

ls -t	sort by time of last change
	-tr sorts in reverse time order
	-ltr is my most common ls command: lists newest at the end

cp f1 f2	copy file f1 to file f2

cat f	"concatenate": print file f
	cat f1 f2 ... prints files in order

more f	print f a screen at a time.  "less" is a synonym

head f	print first 10 lines of f; head -N prints N

tail f	print last 10 lines of f; tail -N prints N

mv f1 f2	"move" renames f1 to f2

rm f	remove f  (really removes it: there is no backup copy)
	rm f1 f2 ...

cmp f1 f2	compare f1 with f2

diff f1 f2	"differences": a more helpful display of
		how f1 and f2 differ

wc f	word count: print number of lines, words and characters in f
	wc f1 f2 ...

grep re f	print all lines in f that match regular	expression re
	grep re f1 f2 ...

sort f	sort file f into alphabetical order by line

du	"disk usage": prints a summary of all the directories
	and how much space they are using.  Best used as
	du -k or du -m for space in KB or MB.

du -a	the same, but for all files; very useful for finding out
	what's in part of the file system hierarchy.

ls -R	runs ls recursively, so it does much the same


FILENAME PATTERNS

Almost all Unix commands deal with multiple input files.  You can
specify a list of files with shorthands (often called wild cards),
patterns that match a set of files in a directory.

The most frequently-used is *, which matches any sequence of
characters in a name.  So:

wc *	counts words, lines and characters in all files in the
	current directory

wc *.txt	does the same but only for files whose names
		end in .txt

wc s*.txt	the same, but names start with s and end with .txt

The character ? matches a single character of a filename, so

wc s???		runs wc on all files with 4-letter names that
		start with s.



INPUT-OUTPUT REDIRECTION AND PIPES

You can capture the output of any program in a file instead of
having it show up on the screen by redirecting output with >:

any.program ... >output.file

The matching < tells a program to take its input from a file:

any.program <input.file

This is most often used with programs that normally take their
input from the keyboard.

You can direct the output of any program into the input of
any other program with a pipe "|".

grep re s??? | wc	count occurrences of re in the "s" files

ls -R | grep sonnet	find all files whose names contain sonnet

The pipe mechanism is perhaps the greatest single innovation
of Unix.  Learn how to use it.


QUOTING

Sometimes it's necessary to disable the special meaning of 
characters like * or ?, or include a character like space
in something, for example using grep to look for lines that
have multiple spaces:

grep '  ' s*

Quoting is a bit subtle, but generally you can use '...' to
prevent special characters from being interpreted as filename
shorthands or i/o redirection.