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?
perl -pe 'chop if eof' filename >filename2
This was described as a 'perl blasphemy' on the awk website I saw.
But, in a test, it worked.
head -n -1 abc > newfile
tail -n 1 abc | tr -d '\n' >> newfile
Edit 2:
Here is an awk version (corrected) that doesn't accumulate a potentially huge array:
awk '{if (line) print line; line=$0} END {printf $0}' abc
The only time I've wanted to do this is for code golf, and then I've just copied my code out of the file and pasted it into an echo -n 'content'>file statement.
If you want to do it right, you need something like this:
use autodie qw(open sysseek sysread truncate);
my $file = shift;
open my $fh, '+>>', $file;
my $pos = tell $fh;
sysseek $fh, $pos - 1, 0;
sysread $fh, my $buf, 1 or die 'No data to read?';
if($buf eq "\n"){
truncate $fh, $pos - 1;
}
We open the file for reading and appending; opening for appending means that we are already seeked to the end of the file. We then get the numerical position of the end of the file with tell. We use that number to seek back one character, and then we read that one character. If it's a newline, we truncate the file to the character before that newline, otherwise, we do nothing.
This runs in constant time and constant space for any input, and doesn't require any more disk space, either.
Here is a nice, tidy Python solution. I made no attempt to be terse here.
This truncates a file by two bytes if the last two bytes are CR/LF, or by one byte if the last byte is LF. It does not attempt to modify the file if the last byte(s) are not (CR)LF. It handles errors. Tested in Python 2.6.
Put this in a file called "striplast" and chmod +x striplast.
#!/usr/bin/python
# strip newline from last line of a file
import sys
def trunc(filename, new_len):
try:
# open with mode "append" so we have permission to modify
# cannot open with mode "write" because that clobbers the file!
f = open(filename, "ab")
f.truncate(new_len)
f.close()
except IOError:
print "cannot write to file:", filename
sys.exit(2)
# get input argument
if len(sys.argv) == 2:
filename = sys.argv[1]
else:
filename = "--help" # wrong number of arguments so print help
if filename == "--help" or filename == "-h" or filename == "/?":
print "Usage: %s <filename>" % sys.argv[0]
print "Strips a newline off the last line of a file."
sys.exit(1)
try:
# must have mode "b" (binary) to allow f.seek() with negative offset
f = open(filename, "rb")
except IOError:
print "file does not exist:", filename
sys.exit(2)
SEEK_EOF = 2
f.seek(-2, SEEK_EOF) # seek to two bytes before end of file
end_pos = f.tell()
line = f.read()
f.close()
if line.endswith("\r\n"):
trunc(filename, end_pos)
elif line.endswith("\n"):
trunc(filename, end_pos + 1)
P.S. In the spirit of "Perl golf", here's my shortest Python solution. It slurps the whole file from standard input into memory, strips all newlines off the end, and writes the result to standard output. Not as terse as the Perl; you just can't beat Perl for little tricky fast stuff like this.
Remove the "\n" from the call to .rstrip() and it will strip all white space from the end of the file, including multiple blank lines.
Put this into "slurp_and_chomp.py" and then run python slurp_and_chomp.py < inputfile > outputfile.
import sys
sys.stdout.write(sys.stdin.read().rstrip("\n"))
Using dd:
file='/path/to/file'
[[ "$(tail -c 1 "${file}" | tr -dc '\n' | wc -c)" -eq 1 ]] && \
printf "" | dd of="${file}" seek=$(($(stat -f "%z" "${file}") - 1)) bs=1 count=1
#printf "" | dd of="${file}" seek=$(($(wc -c < "${file}") - 1)) bs=1 count=1
Assuming Unix file type and you only want the last newline this works.
sed -e '${/^$/d}'
It will not work on multiple newlines...