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I need to find ONLY the lines that start with the string G1 Z, and then replace any occurrence on that same line of F1800 with a new value of F500. For example:

G1 Z9.800 F1800.000 ; move to next layer (48)
G1 X103.711 Y99.145 F1800.000 ; move to first perimeter point
G1 X96.289 Y96.289 E320.13685 ; perimeter
G1 Z0.000 F1800.000 ; move to next layer (49)
G1 X103.711 Y96.289 E320.44978 ; perimeter
G1 X103.711 Y99.070 E320.56702 ; perimeter
G1 X95.782 Y104.218 E321.13977 F1800.000 ; perimeter

Should become:

G1 Z9.800 F500.000 ; move to next layer (48)
G1 X103.711 Y99.145 F1800.000 ; move to first perimeter point
G1 X96.289 Y96.289 E320.13685 ; perimeter
G1 Z10.000 F500.000 ; move to next layer (49)
G1 X103.711 Y96.289 E320.44978 ; perimeter
G1 X103.711 Y99.070 E320.56702 ; perimeter
G1 X95.782 Y104.218 E321.13977 F1800.000 ; perimeter

I know /^G1 Z will find these lines, and %s/F1800/F500/g will replace ALL F1800s, but I can't see how to restrict the replace to the lines starting with that string.

I'm on GVIM 8.0.586.

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2 Answers 2

Reset to default
6

Try:

:g/^G1 Z/s/F1800/F500/g

The :g is the "global" command. It selects lines with a regular expression and then executes a command on it.

Here it selects lines that start with G1 Z and then substitutes all "F1800" with "F500" in this line.

BTW:

  • The default command for :g is print. So by just executing :g/^G1 Z/ Vim will print all lines that start with G1 Z.
  • There is also the :v/.../ command. It selects all lines that does not match the given regular expression.

See :help multi-repeat.

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The following command uses look behind regex pattern:

:%s/\v(^G1 Z.*)@<=F1800/F500/g
  • %s starts the substitution in the whole file.
  • / starts the find part of the find and replace.
  • \v enables very-magic (see :h /magic)
  • (^G1 Z.*)@<= looks behind for lines starting with G1 Z. But it doesn't start the matching. (see :h /\@<=)
  • F1800 starts matching for, well, F1800.
  • / starts the replace part of find and replace.
  • F500 replaces the matched pattern
  • / finishes the replace pattern
  • g is for global substitution, so that all the instances of F1800 will be replaced by F500. (see :h :s_flags)
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  • Can also use \zs. e.g. :%s/^G1 Z.*\zsF1800/F500/
    – Peter Rincker
    Mar 20, 2019 at 19:06
  • Thanks for the answer and detailed explanation. I found the other answer easier to follow.
    – Davo
    Mar 20, 2019 at 19:25
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    @PeterRincker but that wouldn't work if there are more than one F1800 in a line
    – 3N4N
    Mar 20, 2019 at 19:29
  • @Davo yes. I just wanted to see if I could get the solution. I learnt about @<= today. Although I know using :g/pattern/cmd is more intuitive in cases like this. By the way, does it work?
    – 3N4N
    Mar 20, 2019 at 19:32
  • 1
    Yes, both answers and @PeterRincker's example all worked. :)
    – Davo
    Mar 20, 2019 at 19:39

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