Remove blank lines from the ends of a bunch of files

Question

I have a bunch of files with many lines in them, and usually one or two blank lines at the end.

I want to remove the blank lines at the end, while keeping all of the blank lines that may exist within the file.

I want to restrict the operation to the use of GNU utilities or similar, ie bash, sed, awk, cut, grep etc.

I know that I can easily remove all blank lines, with something like:

sed '/^$/d'

But I want to keep blank lines which exist prior to further content in the file.

File input might be as follows:

line1
line2

line4
line5

I'd want the output to look like:

line1
line2

line4
line5

All files are <100K, and we can make temporary copies.

Answer 1

With Perl:

perl -0777 -pe 's/\n*$//; s/$/\n/' file

Second S command ( s/$/\\n/ ) appends again a newline to end of your file to be POSIX compilant.

Or shorter:

perl -0777 -pe 's/\n*$/\n/' file

With Fela Maslen's comment to edit files in place ( -i ) and glob all elements in current directory ( * ):

perl -0777 -pe 's/\n*$/\n/' -i *

Answer 2

Here is an awk solution (Standard linux gawk ). I enjoyed writing.

single line:

awk '/^\s*$/{s=s $0 ORS; next}{print s $0; s=""}' input.txt

using a readable script script.awk

    /^\s*$/{skippedLines = skippedLines $0 ORS; next}
    {print skippedLines $0; skippedLines= ""}

explanation:

/^\s*$/ {                   # for each empty line
    skippedLines = skippedLines $0 ORS; # pad string of newlines
    next;                   # skip to next input line
}
{                           # for each non empty line
    print skippedLines $0;  # print any skippedLines and current input line
    skippedLines= "";       # reset skippedLines
}

Answer 3

If lines containing just space chars are to be considered empty:

$ tac file | awk 'NF{f=1}f' | tac
line1
line2

line4
line5

otherwise:

$ tac file | awk '/./{f=1}f' | tac
line1
line2

line4
line5

Answer 4

This might work for you (GNU sed):

sed ':a;/\S/{n;ba};$d;N;ba' file

If the current line contains a non-space character, print the current pattern space, fetch the next line and repeat. If the current line(s) is/are empty and it is the last line in the file, delete the pattern space, otherwise append the next line and repeat.