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Top Forums Shell Programming and Scripting sed one liner to Delete blank lines - Help required Post 302942259 by TomG on Monday 27th of April 2015 01:32:29 AM
Old 04-27-2015
sed one liner to Delete blank lines - Help required

Hi,

Code:
cat test.txt
BlankLine
BlankLine
BlankLine
BlankLine
ello
hi
helo
BlankLine
BlankLine
heylo
BlankLine
BlankLine
BlankLine
done
BlankLine
BlankLine
BlankLine

The above is the content of the file.(blank lines in between lines,at the begining of file and at the end of the file)

I am applying the following sed command

Code:
 sed '/^$/N;/\n$/D' test.txt

the output is

Code:
BlankLine
ello
hi
helo
BlankLine
heylo
BlankLine
done

Note : inorder to represent a blank line i have used 'BlankLine'.
My doubt is how 1 blank line in begining and 1 blank line in between the lines are preserved. Also all blank lines at the end are removed.

Can anyone please explain this.?


Thank You
 

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cat(1)							      General Commands Manual							    cat(1)

Name
       cat - concatenate and print data

Syntax
       cat [ -b ] [ -e ] [ -n ] [ -s ] [ -t ] [ -u ] [ -v ] file...

Description
       The  command reads each file in sequence and displays it on the standard output.  Therefore, to display the file on the standard output you
       type:
       cat file
       To concatenate two files and place the result on the third you type:
       cat file1 file2 > file3
       To concatenate two files and append them to a third you type:
       cat file1 file2 >> file3
       If no input file is given, or if a minus sign (-) is encountered as an argument, reads from the standard input file.  Output is buffered in
       1024-byte blocks unless the standard output is a terminal, in which case it is line buffered.  The utility supports the processing of 8-bit
       characters.

Options
       -b   Ignores blank lines and precedes each output line with its line number.

       -e   Displays a dollar sign ($) at the end of each output line.

       -n   Precedes all output lines (including blank lines) with line numbers.

       -s   Squeezes adjacent blank lines from output and single spaces output.

       -t   Displays non-printing characters (including tabs) in output.  In addition to those representations used with the -v  option,  all  tab
	    characters are displayed as ^I.

       -u   Unbuffers output.

       -v   Displays  non-printing  characters (excluding tabs and newline) as the ^x.	If the character is in the range octal 0177 to octal 0241,
	    it is displayed as M-x. The delete character (octal 0177) displays as ^?.  For example, is displayed as ^X.

See Also
       cp(1), ex(1), more(1), pr(1), tail(1)

																	    cat(1)
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