shifting decimal point using vim, shell or python

Question

I have a .pl file that consists of an unstructured header and some specific X Y Z structure. The header has no "." in there. Below you can find a snippet of this file:

Header (in total 29 lines)
ILINE
VRTX 1 545057.78564453125 3800905.201171875 -15000 
VRTX 2 545184.49072265625 3800765.451171875 -15000 
VRTX 3 545310.91650390625 3800625.970703125 -15000 
SEG 1 2 
SEG 2 3 
ILINE
VRTX 136 551295.84606933594 3799015.443359375 -15000 
VRTX 137 551293.82849121094 3798841.880859375 -15000 
VRTX 138 551290.57849121094 3798661.892578125 -15000  
SEG 136 137 
SEG 137 138 

What I like to achieve is to shift the decimal point of my X and Y values to the left like this:

VRTX 1 5450.5778564453125 38009.05201171875 -15000 
VRTX 2 5451.8449072265625 38007.65451171875 -15000 
VRTX 3 5453.1091650390625 38006.25970703125 -15000

I think that regular expressions could help but I have no experiences in that using Python nor Shell. Any help is appreciated.

Answer 1

A copy and paste friendly vim solution

:g/VRTX/normal f.xhhP;xhhP

explanation:

• :g/{pattern}/command - executes command on every line matching pattern. In this case every VRTX line
• normal - the commands we want to execute are normal mode commands
• f. - find the first dot in current line
• xhhP - cut such character, move left two times, paste
• ; - find next occurrence
• xhhP - move dot again

Answer 2

Since there is a vim tag on the question:

/\.
qaqqanx2hi!<esc>@aq
@a
:%s/!/./g

Assuming there is no ! in the text, else you have to substitute it with a different character(s). Of course there are other solutions in vim, but that's the simplest which I can think of right now.

Breakdown:

 /\.                  " searches every `.` in the file 
                      " (and "marks" them as searchresults)

qaqqanx2hi!<esc>@aq   " Our macro we use:
qaq                   " records an empty macro into register a 
                      " (This ensures the register is empty)
   qa                 " This starts recording a macro into register a again
     nx2hi!<esc>      " `n` jumps to the next search result,  
                      " `2hxhi!<esc>` inserts a `!` 2 chars left of where
                      " the `.` has been, and exits insert mode
                @a    " calls the macro at register `a`, since we emptied it,
                      " nothing happens yet, but once we save this macro it will
                      " be in register `a`. So it will call itself until it 
                      " reaches an abort conditions (no more `.` found in the
                      " text, thats why we replace `.` with `!` here, else
                      " the macro would move the `.` over and over to the left
                  q   " Stops recording the macro and saves it (to register `a`)

@a                    " calls the macro in register `a`

:%s/!/./g             " This just replaces all `!` in the file with `.`

Possible cleaner solution: Use nowrapscan (thanks @Francesco)

/\.
:set nows
qaqqax3hpn@aq
@a
:set ws

Note: The Macro changes order a bit. We must first change the position of the . and then jump to the next search-occurence else we will miss the first occurence, since the search doesn't wrap arround eof anymore.

Note: It would be better to save the state of ws before and then restore it. But that would only matter in a generic version.

Conclusion

Complicated but flexible solution. If you don't need to be flexible, the other vim solutions here are easier (I will not judge other solutions)