Filter(s)	Use
cat	"Catenate" a file.
base64	Encode/decode "ASCII armor"
diff	Take the difference in two files
grep/egrep/fgrep	Apply regular expressions to a bytesream
fmt/pr/nl	Apply formatting to a file.
head/tail	Show the initial/final lines of a bytestream.
less/more/pg	Display one page at a time.
cut/paste	Excerpt and join input.
sort	Sort
tr	Transform a bytestream.
uniq	Find/Remove/Count unique lines in a bytestream.
spell	Find problematic spellings (ispell is great for interactively fixing spelling problems.)
xargs	Build and execute command lines from standard input
sed	The stream editor; arbitrarily modify lines in a bytestream.