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Full Discussion: sed question - change 2d to last line in file
Top Forums UNIX for Dummies Questions & Answers sed question - change 2d to last line in file Post 302525947 by agama on Sunday 29th of May 2011 09:11:36 PM
Old 05-29-2011
Here's a single pass sed that should work. I've put each command on a separate line to make it more clear.

Code:
sed '
$ b last
/^$/ b blank
H
d
b
:blank
x
p
d
x
b
:last
x
s/This is line 4/New Line Four/
p
x
' tdata

I tested this with GNU sed version 4.1.5.

I've not added an explanation of the logic on the off chance that you'd like to figure it out; I'd be happy to if you'd like.

There is a big assumption that you know the line 4 text to put into a substitute command. If it's not known, this won't work, but from your description I believe you do know it.

The one liner is below:

Code:
' $ b last; /^$/ b blank; H; d; b; :blank x; p; d; x; b; : last x; s/This is line 4/new line 4/; p; x' tdata

 

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LEARN ABOUT PHP

g3cat

g3cat(1)						       mgetty+sendfax manual							  g3cat(1)

NAME

       g3cat - concatenate multiple g3 documents

SYNOPSIS

       g3cat [-l] [-a] g3-file1 ...

DESCRIPTION

       g3cat  concatenates  g3	files.	These can either be 'raw', that is, bitmaps packed according to the CCITT T.4 standard for one-dimensional
       bitmap encoding, or 'digifax' files, created by GNU's GhostScript package with the digifax drivers. Its output is a  concatenation  of  all
       the input files, in raw G3 format, with two white lines in between.

       If a - is given as input file, stdin is used.

       If the input data is malformed, a warning is printed to stderr, and the output file will have a blank line at this place.

OPTIONS

       -l     separate files with a one-pixel wide black line.

       -h <blank lines>
	      specifies the number of blank lines g3cat should prepend to each page. Default is 0.

       -L <lines>
	      limit lenght of output page to maximum <lines> lines.

SPECIAL-CASE OPTIONS
       -w <width>
	      specifies  the  desired  page width in pixels per line. Default is 1728 PELs, and this is mandatory if you want to send the fax to a
	      standard fax machine.  If one of the input files doesn't match this line width (for example because it was created by  a	broken	G3
	      creator), a warning is printed, and the line width is transparently fixed.

       -a     byte-align the end-of-line codes (EOL) in the file. Every EOL will end at a byte boundary, that is, with a  01 byte.

       -p <pad>
	      specifies a minimum number of bytes that each output line must be padded to.  Padding is done with 0-bits before the EOL code.

       -R     suppress output of end-of-page code (RTC).

Example
       The following example will put a header line on a given g3 page, 'page1' and put the result into 'page2':

       echo '$header' | pbmtext | pbm2g3 | g3cat - page1 >page2

FILES

       --

BUGS

       Hopefully none :-).

SEE ALSO

       g32pbm(1), sendfax(8), faxspool(1)

AUTHORS

       g3cat is Copyright (C) 1993 by Gert Doering, <gert@greenie.muc.de>

greenie 							     27 Oct 93								  g3cat(1)
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