How can I remove all but the first n characters of a every line in the file buffer?
What I tried
Mark region
C-x r k #but this is cumbersome when the length of lines are very varied, and there are over 100 lines
asked Feb 8, 2018 at 18:29
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Try rectangle editing.– Dan ♦Commented Feb 8, 2018 at 18:52
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rectangle editing misses segments when some lines in the middle are lengthy– american-ninja-warriorCommented Feb 8, 2018 at 20:06
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Well... rectangle editing does what you tell it to do -- if it 'misses' segments it's because you didn't make your rectangle the appropriate width. (I do know what you mean though -- it might not be obvious what the necessary width is, and it can indeed be a cumbersome solution.)– philsCommented Feb 8, 2018 at 21:10
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1 Answer
You can do a replace-regexp like this:
- replace
^\(.\{15\}\).*$ - with
\1
This will match lines with at least 15 characters, and replace with the 1st 15 (which are saved as a match group).
Did you mention that n=15?
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2E.g.,
(defun foo (beg end &optional n) (interactive "r\np") (let ((rgx (format "^\\(.\\{%d\\}\\).*$" n))) (replace-regexp rgx "\\1" nil beg end)))– DrewCommented Feb 8, 2018 at 20:55 -