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Top Forums Shell Programming and Scripting SED delete only first line command - Help need Post 302441270 by gwgreen1 on Friday 30th of July 2010 03:57:49 AM
Old 07-30-2010
Error SED delete only first line command - Help need

Can any one help me how the sed delete only first line command (D) works.
Code:
sed -f sedcmds File.txt

In this how the sed delete only first line command (D) works to delete the blank lines appearing more than ones leaving only one blank and deleting others blanks.
While doing step by step when two blank line appended in the pattern space, according to D command one blank is deleted in the pattern space leaving second one alone.
My question is what will happen to the remaining blank space, whether it will send as output immediately by clearing pattern space or append next pattern to that blank space???. After this how the next loop will start?
Can u explain this detailly... coz I couldn't able to find the detailed explanation for sed's D delete command in net.

sedcmds
Code:
/^$/{
       N
       /^\n$/D
       }

File.txt
Code:
This is line1

This is line2


this is line3




This is line4.

Moderator's Comments:
Mod Comment Having 14 posts in this forum, you should be familiar with using code tags.

Last edited by zaxxon; 07-30-2010 at 05:11 AM..
 

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diffmk(1)							   User Commands							 diffmk(1)

NAME
diffmk - mark differences between versions of a troff input file SYNOPSIS
diffmk oldfile newfile markedfile DESCRIPTION
diffmk compares two versions of a file and creates a third version that includes "change mark" (.mc) commands for nroff(1) and troff(1). oldfile and newfile are the old and new versions of the file. diffmk generates markedfile, which, contains the text from newfile with troff(1) "change mark" requests (.mc) inserted where newfile differs from oldfile. When markedfile is formatted, changed or inserted text is shown by | at the right margin of each line. The position of deleted text is shown by a single *. USAGE
See largefile(5) for the description of the behavior of diffmk when encountering files greater than or equal to 2 Gbyte ( 2**31 bytes). EXAMPLES
Example 1: An example of the diffmk command. diffmk can also be used in conjunction with the proper troff requests to produce program listings with marked changes. In the following command line: example% diffmk old.c new.c marked.c ; nroff reqs marked.c | pr the file reqs contains the following troff requests: .pl 1 .ll 77 .nf .eo .nh which eliminate page breaks, adjust the line length, set no-fill mode, ignore escape characters, and turn off hyphenation, respectively. If the characters | and * are inappropriate, you might run markedfile through sed(1) to globally change them. ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Availability |SUNWdoc | +-----------------------------+-----------------------------+ SEE ALSO
diff(1), nroff(1), sed(1), troff(1), attributes(5), largefile(5) BUGS
Aesthetic considerations may dictate manual adjustment of some output. File differences involving only formatting requests may produce undesirable output, that is, replacing .sp by .sp 2 will produce a "change mark" on the preceding or following line of output. SunOS 5.10 14 Sep 1992 diffmk(1)
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