sed
awk
tr
grep
find
sort
diff
cmp
join
rev
cut
${#}
IFS
set
| (pipe)
tmp
> 2>
head
tail
tee
spell
date
wc
cat
&& ||
() >
pr

eval
eval example
A=USER
eval $A
the above prints skarnam

these are equivalent
for i in $(ls) ; do XXX ; done
for i in * ; do XXX ; done

A=$(cat login.password)
A=$(< login.password)

to filter on stderr
# standard error is now pointing to where standard output is, output is then
# changed to point to null
ls hola 2>&1 > /dev/null

# multiline comment
: '
this is a multiline
comment.
this is line3 of the
multiline comment.
'