Suppose I have a file called file:
$ cat file
Hello
Welcome to
Unix
I want to add and Linux at the end of the last line of the file. If I do echo " and Linux" >> file will be added to a new line. But I want last line as Unix and Linux
So, in order to work around this, I want to remove newline character at the end of file. Therefore, how do I remove the newline character at the end of file in order to add text to that line?
If all you want to do is add text to the last line, it's very easy with sed. Replace $ (pattern matching at the end of the line) by the text you want to add, only on lines in the range $ (which means the last line).
sed '$ s/$/ and Linux/' <file >file.new &&
mv file.new file
which on Linux can be shortened to
sed -i '$ s/$/ and Linux/' file
If you want to remove the last byte in a file, Linux (more precisely GNU coreutils) offers the truncate command, which makes this very easy.
truncate -s -1 file
A POSIX way to do it is with dd. First determine the file length, then truncate it to one byte less.
length=$(wc -c <file)
dd if=/dev/null of=file obs="$((length-1))" seek=1
Note that both of these unconditionally truncate the last byte of the file. You may want to check that it's a newline first:
length=$(wc -c <file)
if [ "$length" -ne 0 ] && [ -z "$(tail -c -1 <file)" ]; then
# The file ends with a newline or null
dd if=/dev/null of=file obs="$((length-1))" seek=1
fi
perl -pi -e 'chomp if eof' myfile. Compared to truncate or dd it not gonna leave you with a broken file if myfile had actually no trailing newlines.
You can achieve this with perl as:
perl -pi -e 'chomp if eof' myfile
Compared to truncate or dd this not gonna leave you with a broken file if myfile had actually no trailing newlines.
(the answer is constructed from the comment, and based on this answer)
function chomp() { perl -p -e 'chomp if eof' }. Now I can strip a new line with a pipe like this: cat /tmp/file | chomp.
Though, you can remove newline character from all lines by using tr -d '\n':
$ echo -e "Hello"
Hello
$ echo -e "Hello" | tr -d '\n'
Hello$
You can remove the newline character at the end of file using following easy way:
head -c -1 fileFrom man head:
-c, --bytes=[-]K
print the first K bytes of each file; with the leading '-',
print all but the last K bytes of each file
truncate -s -1 filefrom man truncate:
-s, --size=SIZE
set or adjust the file size by SIZE
head -c -1 file | tee file safe? Wouldn't tee truncate the file before starting?
tee only has to open the file, whereas head has to read and write its contents, tee will in practice win the race except sometimes for very small files.
Commented
Jan 11, 2016 at 22:46
Here's one way with sed -- on the last ($) line of the file, search and replace anything and everything (.*) with "whatever you matched" followed by " and Linux":
sed '$s/\(.*\)/\1 and Linux/' file
An even simpler solution, courtesy of Isaac, is:
sed '$s/$/ and Linux/' file
This replaces the (symbolic) end-of-line with the given text.
perl -0pi -e "s/\R\z//g" file
Works for "\r" (MAC), "\r\n" (Windows) and "\n" (Linux). For repeated newlines (any tipe) at end of file you can do:
perl -0pi -e "s/\R*\z//g" file
sed '$s/$/ and linux/'