Remove leading blanks on all lines:
*s/^ *//
Remove trailing blanks on all lines:
*s/ *$//
Reverse order of all lines:
*m0
Duplicate all lines:
*k$
Duplicate current line:
.k.
Print first 4 lines after each "function":
g/function/.,.+4p
Delete all empty lines:
g/^$/d
Delete all lines which contain only spaces or are empty:
g/^ *$/
Delete all lines containing the word comment:
g/comment/d
Place a "," after each "however":
g/however/s//&,/
Place a line containing the word "end" after each "begin":
g/begin/a end
Turn runs of spaces into tabs:
s/@(t)/\01/s/ *\01/\09/