Question 220346 in Ubuntu Question posted in
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I need to remove white spacing for lines that are separated by white spacing, in a .txt file, from Ubuntu

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Hello!!

As it says in the title, I need to remove the white spacing that separate only by a white spacing to two lines, as you see in the image, the white spacing that have a green line, are the ones I need to remove, but the multiple white spacing that are with a red line, I do not want to remove them, the ones with the green line, are separated by only a white spacing, I do not know if with AWK or SED or CUT will work, the problem is that I do not know how to do it, thank you for your help.

I tried to do it with SED and with AWK as follows, but it did not produce any effect

awk -F, '{gsub("n","",$1); print}' archivo.txt

sed 's/ //g' input.txt > no-spaces.txt
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3

Answers


  1. 0

    Assumptions:

    • The input file has "n" (not "rn") line endings.
    • Non-empty line contains at least two charactes.
    • We don’t have to care about an empty line at the beginning or the ending
      of the file.

    If GNU sed which supports -z (slurp) option and n notation is
    available. would you please try:

    sed -Ez "s/([^n]n)n([^n])/12/g" input.txt > no-spaces.txt

    Example of input.txt:

    line1
line2 # following blank line should be removed

line3 # following blank lines should be kept



line4

    Output:

    line1
line2 # following blank line should be removed
line3 # following blank lines should be kept



line4

    Sed normally processes the input line by line. That is why we cannot process
    the input across multiple lines. The -z option changes the behavior by
    setting the input line separator to the NUL character.

    • ([^n]n) matches the last character of non-blank line. 1 is set as a bac
      kreference.
    • n is the blank line in between (to be removed).
    • ([^n]) matches the first character of the following non-blank line. 2 is
      set as a backreference.

    Btw following will work with any POSIX-compliant sed with a help of bash:

    #!/bin/bash

# define newline character for replacement
NL=$'\n'

sed -E '
:l
N
$!b l
# first slurp all lines in the pattern space
# and perform the replacements over the lines
s/([^'"$NL"']'"$NL"')'"$NL"'([^'"$NL"'])/12/g
' input.txt > no-spaces.txt
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  2. 0

    With any awk:

    awk '/^[[:space:]]*$/{n++; p=$0; next} {if(n==1) print p; print; n=0}' file

    If the current line contains only spaces (/^[[:space:]]*$/) increment variable n, store current line in variable p, and move to next line (next). Else (the current line contains non-space characters), if n==1 print the previous empty line stored in variable p, then print the current line and reset n.

    Note: if the last line contains only spaces and is preceded by a line containing non-space characters, it is not printed. If it must be printed try:

    awk '/^[[:space:]]*$/{n++; p=$0; next} {if(n==1) print p; print; n=0}
  END {if(n==1) print p}' file

    Note: if you want to remove only empty lines, replace ^[[:space:]]*$/ with /^$/.

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  3. 0

    This might work for you (GNU sed):

    sed -E '1N;:a;N;/(S.*n)n(.*S)/{s//12/;N;ba};P;D' file

    Open a 3 line window.

    If a two non-empty lines sandwich an empty line, remove the empty line and maintain the 3 line window.

    Otherwise, print/delete the first line and repeat.

    N.B. 1N ensures the 3 line window is created, the N following the substitution ensures this likewise.

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