How can I delete a newline if it is the last chara

Question

I have some files that I'd like to delete the last newline if it is the last character in a file. od -c shows me that the command I run does write the file with a trailing new line:

0013600   n   t  >  \n

I've tried a few tricks with sed but the best I could think of isn't doing the trick:

sed -e '$s/\(.*\)\n$/\1/' abc

Any ideas how to do this?

Answer 1

You can do this with head from GNU coreutils, it supports arguments that are relative to the end of the file. So to leave off the last byte use:

head -c -1

To test for an ending newline you can use tail and wc. The following example saves the result to a temporary file and subsequently overwrites the original:

if [[ $(tail -c1 file | wc -l) == 1 ]]; then
  head -c -1 file > file.tmp
  mv file.tmp file
fi

You could also use sponge from moreutils to do "in-place" editing:

[[ $(tail -c1 file | wc -l) == 1 ]] && head -c -1 file | sponge file

---

You can also make a general reusable function by stuffing this in your .bashrc file:

# Example:  remove-last-newline < multiline.txt
function remove-last-newline(){
    local file=$(mktemp)
    cat > $file
    if [[ $(tail -c1 $file | wc -l) == 1 ]]; then
        head -c -1 $file > $file.tmp
        mv $file.tmp $file
    fi
    cat $file
}

Update

As noted by KarlWilbur in the comments and used in Sorentar's answer, truncate --size=-1 can replace head -c-1 and supports in-place editing.

Answer 2

You can take advantage of the fact that shell command substitutions remove trailing newline characters:

Simple form that works in bash, ksh, zsh:

printf %s "$(< in.txt)" > out.txt

Portable (POSIX-compliant) alternative (slightly less efficient):

printf %s "$(cat in.txt)" > out.txt

Note:

• If in.txt ends with multiple newline characters, the command substitution removes all of them - thanks, @Sparhawk. (It doesn't remove whitespace characters other than trailing newlines.)
• Since this approach reads the entire input file into memory, it is only advisable for smaller files.
• printf %s ensures that no newline is appended to the output (it is the POSIX-compliant alternative to the nonstandard echo -n; see http://pubs.opengroup.org/onlinepubs/009696799/utilities/echo.html and https://unix.stackexchange.com/a/65819)

---

A guide to the other answers:

• If Perl is available, go for the accepted answer - it is simple and memory-efficient (doesn't read the whole input file at once).

• Otherwise, consider ghostdog74's Awk answer - it's obscure, but also memory-efficient; a more readable equivalent (POSIX-compliant) is:

  • awk 'NR > 1 { print prev } { prev=$0 } END { ORS=""; print }' in.txt
  • Printing is delayed by one line so that the final line can be handled in the END block, where it is printed without a trailing \n due to setting the output-record separator (OFS) to an empty string.

• If you want a verbose, but fast and robust solution that truly edits in-place (as opposed to creating a temp. file that then replaces the original), consider jrockway's Perl script.

Answer 3

Assuming Unix file type and you only want the last newline this works.

sed -e '${/^$/d}'

It will not work on multiple newlines...

* Works only if the last line is a blank line.

Answer 4

ruby:

ruby -ne 'print $stdin.eof ? $_.strip : $_'

or:

ruby -ane 'q=p;p=$_;puts q if $.>1;END{print p.strip!}'

Answer 5

$  perl -e 'local $/; $_ = <>; s/\n$//; print' a-text-file.txt

See also Match any character (including newlines) in sed.

Answer 6

Yet another answer FTR (and my favourite!): echo/cat the thing you want to strip and capture the output through backticks. The final newline will be stripped. For example:

# Sadly, outputs newline, and we have to feed the newline to sed to be portable
echo thingy | sed -e 's/thing/sill/'

# No newline! Happy.
out=`echo thingy | sed -e 's/thing/sill/'`
printf %s "$out"

# Similarly for files:
file=`cat file_ending_in_newline`
printf %s "$file" > file_no_newline