making each line double vim

Try this:

:%s/.*/echo "\0"\rcat \0/g

Explanation:

:%s/a/b/g means search whole file and replace a to b.

.* means match every thing in one line.

\0 means the matched thing.

\r means the new line.

alternatively you could apply a macro

yypha"<esc>^iecho "<esc>j^icat <esc>j

• yypha" yanks the current line puts it below the current and go up with h
• a"<esc> appends a " and goes back to normal mode
• ^iecho "<esc> puts echo " in front of the file* and again goes to normal
• j^icat<esc> prepends cat on the next line and
• j at last goes to the next line to be ready for reapplying the macro

you can either record the macro by pressing qq and the buttons as described or

write yypha"^[^iecho "^[j^icat ^[j with ^[ being entered as Ctrl-V then Esc and then "qyy to yank the line in the q-th register, which is then also an executable macro.

The macro itself you can run with @q once or 30@q thirty times.

I'd usually go with the accepted answer, but just to show that command-mode (Ex) commands can be nice too:

:g/^./t. | norm! icat␣^Ok^O0echo␣"^OA"

^{Note: enter the keycodes using ^V (e.g. ^V^O). On windows, ^Q has that function by default)}

Explanation

• :g/^./ (repeat for every line containing at least one char)
• t. (duplicate the line below)

• the rest:

  • insert `'cat ``,
  • ^Ok (up a line)
  • ^O0 (at start of line)
  • insert 'echo "'
  • append '"' at end of line