The Unix Programming Environment by Kernighan and Pike

Verb      Definition
date      give date & time
who       list active users
pwd       print working directory
man       give manual for
write     send message to

ed        edit
mv        move
cp        copy
rm        remove

ls        alphabetically list files in
ls -l     alphabetically list information on
ls -t     temporally list files in
ls -lt    temporally list information on

cat       concatenate contents of

tail      give last 10 lines of
tail -x   give last x lines of
tail +x   give x to last lines of 

pr        give, 66 lines/page,
pr -x     give, 66 lines/page and x cols/page,
pr -m     give, 66 lines/page in parallel cols,

grep x    give lines matching x in (from ed: g/re/p)
grep -v x give lines not matching

sort      alphabetically sort
sort -r   alphabetically reverse sort
sort -n   numerically sort
sort -nr  numerically reverse sort
sort +x   relative to the x+1st field sort

cmp       give location of 1st difference between
diff      give all differences between

cd        change directory to
mkdir     make directory named
rmdir     remove directory named

echo      echo

x >  y    put the output of x into y
x >> y    append the output of x to y
x <  y    x gets the output of y
x |  y    pipe x to y
x ;  y    run x followed by y
x &       run x in the background

Noun      Definition
/         root directory
.         working|current directory
..        parent of .
x/        directory x
/x/y/z    pathname from root to z via /x/ and /y/
*         a string of characters
?         a single character
[...]     one of the characters ...
'?'       a question mark character
'*'       an asterisks character

leading or trailing '/'s are often elided

C-  control
A-  alternate
F-  function

$ ls -l name.txt
total 104
-rw-r--r--  1 usr  staff   482 Sep  4 13:41 name.txt

Noun        Definition
total 104   blocks on disk occupied by name.txt
-rw-r--r--  read-write permissions
1           links to name.txt
jmeuser     owner of name.txt
482         characters in name.txt
Sep 4 13:41 date and time name.txt was last changed
name.txt    name of name.txt