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Re: Write to a certain line of a file [message #78958 is a reply to message #78957]

Thu, 19 January 2012 08:43

Mark Piper
Messages: 198
Registered: December 2009

Senior Member

On 1/19/2012 5:18 AM, Brian J. Daniel wrote:
> I haven't done this, but POINT_LUN may do what you want. You'd need
> to know the number of bytes per line. You will still have to read the
> entire line, change the bit you want to change, move the LUN back to
> the beginning of the line, and rewrite it.
>
> OpenR, LUN, filename, /Get_Lun
> Point_Lun, LUN, line_number * bytes_per_line
> tmp=''
> ReadF, LUN, tmp
> ; change the line as you see fit
> new_line = tmp + 'changed line!'
> Point_Lun, LUN, line_number * bytes_per_line
> PrintF, LUN, new_line
> Free_Lun, LUN
>
> Code is UNTESTED!

To add to Brian's idea, if you have a text file, use SKIP_LUN with the
LINES keyword set. A crude example:

pro replace_line_ex
compile_opt idl2

f0 = 'ascii.txt'
f1 = 'ascii-1.txt'
file_copy, file_which(f0), f1, /overwrite

nskip = 7
line = ''
replacement = 'My dog has fleas.'

openu, u, f1, /get_lun
skip_lun, u, nskip, /lines
point_lun, -u, mark
readf, u, line
nchars = strlen(line)
point_lun, u, mark
printf, u, replacement, format='(a-' + strtrim(nchars,2) + ')'
free_lun, u
end

Diff 'ascii.txt' in the example/data directory of the IDL distro with
'ascii-1.txt' in your working directory.

mp

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[Message index]

		Re: Write to a certain line of a file By: David Fanning on Thu, 19 January 2012 11:02
		Re: Write to a certain line of a file By: Michael Galloy on Thu, 19 January 2012 09:49
		Re: Write to a certain line of a file By: Mark Piper on Thu, 19 January 2012 08:43
		Re: Write to a certain line of a file By: Brian Daniel on Thu, 19 January 2012 04:18
		Re: Write to a certain line of a file By: Brian Wolven on Wed, 18 January 2012 18:02
		Re: Write to a certain line of a file By: Matt Francis on Wed, 18 January 2012 17:16
		Re: Write to a certain line of a file By: Michael Galloy on Wed, 18 January 2012 12:08
		Re: Write to a certain line of a file By: natha on Wed, 18 January 2012 12:05
		Re: Write to a certain line of a file By: Mark Piper on Fri, 20 January 2012 08:21

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