I piped a program's output on the command line into a file and opened it in vim. At the very end of the file is the character: "^#", what does this mean?
CRTL-# (shown by Vim as ^#) is a NUL character, code point zero in the ASCII table.
You can enter it into Vim while in insert mode with CTRL-vCTRL-#, or by using a tool capable of producing a NUL output:
$ printf "\0" >tempfile
and then check it with any hex dump program:
$ od -xcb tempfile
0000000 0000
\0
000
0000001
So, obviously, your program is outputting NUL at the end for some reason.
Related
The intent of this question is to provide an answer to the daily questions whose answer is "you have DOS line endings" so we can simply close them as duplicates of this one without repeating the same answers ad nauseam.
NOTE: This is NOT a duplicate of any existing question. The intent of this Q&A is not just to provide a "run this tool" answer but also to explain the issue such that we can just point anyone with a related question here and they will find a clear explanation of why they were pointed here as well as the tool to run so solve their problem. I spent hours reading all of the existing Q&A and they are all lacking in the explanation of the issue, alternative tools that can be used to solve it, and/or the pros/cons/caveats of the possible solutions. Also some of them have accepted answers that are just plain dangerous and should never be used.
Now back to the typical question that would result in a referral here:
I have a file containing 1 line:
what isgoingon
and when I print it using this awk script to reverse the order of the fields:
awk '{print $2, $1}' file
instead of seeing the output I expect:
isgoingon what
I get the field that should be at the end of the line appear at the start of the line, overwriting some text at the start of the line:
whatngon
or I get the output split onto 2 lines:
isgoingon
what
What could the problem be and how do I fix it?
The problem is that your input file uses DOS line endings of CRLF instead of UNIX line endings of just LF and you are running a UNIX tool on it so the CR remains part of the data being operated on by the UNIX tool. CR is commonly denoted by \r and can be seen as a control-M (^M) when you run cat -vE on the file while LF is \n and appears as $ with cat -vE.
So your input file wasn't really just:
what isgoingon
it was actually:
what isgoingon\r\n
as you can see with cat -v:
$ cat -vE file
what isgoingon^M$
and od -c:
$ od -c file
0000000 w h a t i s g o i n g o n \r \n
0000020
so when you run a UNIX tool like awk (which treats \n as the line ending) on the file, the \n is consumed by the act of reading the line, but that leaves the 2 fields as:
<what> <isgoingon\r>
Note the \r at the end of the second field. \r means Carriage Return which is literally an instruction to return the cursor to the start of the line so when you do:
print $2, $1
awk will print isgoingon and then will return the cursor to the start of the line before printing what which is why the what appears to overwrite the start of isgoingon.
To fix the problem, do either of these:
dos2unix file
sed 's/\r$//' file
awk '{sub(/\r$/,"")}1' file
perl -pe 's/\r$//' file
Apparently dos2unix is aka frodos in some UNIX variants (e.g. Ubuntu).
Be careful if you decide to use tr -d '\r' as is often suggested as that will delete all \rs in your file, not just those at the end of each line.
Note that GNU awk will let you parse files that have DOS line endings by simply setting RS appropriately:
gawk -v RS='\r\n' '...' file
but other awks will not allow that as POSIX only requires awks to support a single character RS and most other awks will quietly truncate RS='\r\n' to RS='\r'. You may need to add -v BINMODE=3 for gawk to even see the \rs though as the underlying C primitives will strip them on some platforms, e.g. cygwin.
One thing to watch out for is that CSVs created by Windows tools like Excel will use CRLF as the line endings but can have LFs embedded inside a specific field of the CSV, e.g.:
"field1","field2.1
field2.2","field3"
is really:
"field1","field2.1\nfield2.2","field3"\r\n
so if you just convert \r\ns to \ns then you can no longer tell linefeeds within fields from linefeeds as line endings so if you want to do that I recommend converting all of the intra-field linefeeds to something else first, e.g. this would convert all intra-field LFs to tabs and convert all line ending CRLFs to LFs:
gawk -v RS='\r\n' '{gsub(/\n/,"\t")}1' file
Doing similar without GNU awk left as an exercise but with other awks it involves combining lines that do not end in CR as they're read.
Also note that though CR is part of the [[:space:]] POSIX character class, it is not one of the whitespace characters included as separating fields when the default FS of " " is used, whose whitespace characters are only tab, blank, and newline. This can lead to confusing results if your input can have blanks before CRLF:
$ printf 'x y \n'
x y
$ printf 'x y \n' | awk '{print $NF}'
y
$
$ printf 'x y \r\n'
x y
$ printf 'x y \r\n' | awk '{print $NF}'
$
That's because trailing field separator white space is ignored at the beginning/end of a line that has LF line endings, but \r is the final field on a line with CRLF line endings if the character before it was whitespace:
$ printf 'x y \r\n' | awk '{print $NF}' | cat -Ev
^M$
You can use the \R shorthand character class in PCRE for files with unknown line endings. There are even more line ending to consider with Unicode or other platforms. The \R form is a recommended character class from the Unicode consortium to represent all forms of a generic newline.
So if you have an 'extra' you can find and remove it with the regex s/\R$/\n/ will normalize any combination of line endings into \n. Alternatively, you can use s/\R/\n/g to capture any notion of 'line ending' and standardize into a \n character.
Given:
$ printf "what\risgoingon\r\n" > file
$ od -c file
0000000 w h a t \r i s g o i n g o n \r \n
0000020
Perl and Ruby and most flavors of PCRE implement \R combined with the end of string assertion $ (end of line in multi-line mode):
$ perl -pe 's/\R$/\n/' file | od -c
0000000 w h a t \r i s g o i n g o n \n
0000017
$ ruby -pe '$_.sub!(/\R$/,"\n")' file | od -c
0000000 w h a t \r i s g o i n g o n \n
0000017
(Note the \r between the two words is correctly left alone)
If you do not have \R you can use the equivalent of (?>\r\n|\v) in PCRE.
With straight POSIX tools, your best bet is likely awk like so:
$ awk '{sub(/\r$/,"")} 1' file | od -c
0000000 w h a t \r i s g o i n g o n \n
0000017
Things that kinda work (but know your limitations):
tr deletes all \r even if used in another context (granted the use of \r is rare, and XML processing requires that \r be deleted, so tr is a great solution):
$ tr -d "\r" < file | od -c
0000000 w h a t i s g o i n g o n \n
0000016
GNU sed works, but not POSIX sed since \r and \x0D are not supported on POSIX.
GNU sed only:
$ sed 's/\x0D//' file | od -c # also sed 's/\r//'
0000000 w h a t \r i s g o i n g o n \n
0000017
The Unicode Regular Expression Guide is probably the best bet of what the definitive treatment of what a "newline" is.
Run dos2unix. While you can manipulate the line endings with code you wrote yourself, there are utilities which exist in the Linux / Unix world which already do this for you.
If on a Fedora system dnf install dos2unix will put the dos2unix tool in place (should it not be installed).
There is a similar dos2unix deb package available for Debian based systems.
From a programming point of view, the conversion is simple. Search all the characters in a file for the sequence \r\n and replace it with \n.
This means there are dozens of ways to convert from DOS to Unix using nearly every tool imaginable. One simple way is to use the command tr where you simply replace \r with nothing!
tr -d '\r' < infile > outfile
This question already has answers here:
How can I delete a newline if it is the last character in a file?
(23 answers)
Closed 4 years ago.
How to delete the last \n from a file. The file has a last blank line created for a line break in the last text line. I'm using this command:
sed '/^\s*$/d'
But that las blank line is not removed.
Why is sed printing a newline?
When you read the sed POSIX standard, then it states:
Whenever the pattern space is written to standard output or a named file, sed shall immediately follow it with a <newline>.
A bit more details can be found in this answer.
Removing the last <newline>:
truncate: If you want to delete just one-character from a file you can do :
truncate -s -1 <file>
This makes the file one byte shorter, i.e. remove the last character.
From man resize:
-s, --size=SIZE set or adjust the file size by SIZE bytes
SIZE may also be prefixed by one of the following modifying characters:
'+' extend by, '-' reduce by, '<' at most, '>' at least,
'/' round down to multiple of, '%' round up to multiple of.
other answers can be found in How can I delete a newline if it is the last character in a file?
1) DELETE LAST EMPTY LINE FROM A FILE:
First of all, the command you are currently using will delete ALL empty and blank lines!
NOT ONLY THE LAST ONE.
If you want to delete the last line if it is empty/blank then you can use the following command:
sed '${/^[[:blank:]]*$/d}' test
INPUT:
cat -vTE test
a$
$
b$
$
c$
^I ^I $
OUTPUT:
sed '${/^[[:blank:]]*$/d}' test
a
b
c
Explanations:
the first $ will tell sed to do the processing only on the last line
/^[[:blank:]]*$/ the condition will be evaluate by sed and if this line is empty or composed only of blank chars it will trigger the delete operation on the pattern buffer, therefore this last line will not be printed
you can redirect the output of the sed command to save it to a new file or do the changes in-place using -i option (if you use it take a back up of your file!!!!) or use -i.bak to force sed to take a back up of your file before modifying it.
IMPORTANT:
If your file comes from Windows and contain some carriage returns (\r) this sed command will not work!!! You will need to remove those noisy characters by using either dos2unix or tr -d '\r'.
For files containing carriage returns <CR> (\r or ^M):
BEFORE FIXING THE FILE:
cat:
cat -vTE test
a$
$
b$
$
c$
^I ^I ^M$
od:
od -c test
0000000 a \n \n b \n \n c \n \t \t \r \n
0000016
sed:
sed '${/^[[:blank:]]*$/d}' test
a
b
c
AFTER FIXING THE FILE:
dos2unix test
dos2unix: converting file test to Unix format ...
cat:
cat -vTE test
a$
$
b$
$
c$
^I ^I $
od:
od -c test
0000000 a \n \n b \n \n c \n \t \t \n
0000015
sed:
sed '${/^[[:blank:]]*$/d}' test
a
b
c
2) DELETE LAST EOL CHARACTER FROM A FILE:
For this particular purpose, I would recommend using perl:
perl -pe 'chomp if eof' test
a
b
c
you can add -i option to to the change in-place (take a backup of your file before running the command). Last but not least, you might have to remove Carriage Return from your files as described hereover.
Your question isn't clear but this might be what you're asking for:
$ cat file
a
b
c
$ awk 'NR>1{print p} {p=$0}' file
a
b
c
$
you can also use below one-liner from sed to remove the trailing blank line(s):
sed -e :a -e '/^\n*$/N;/\n$/ba'
I'm using linux and when I typed
od -c -N 16 <filename.png>
I got 0000000 211 P N G \r \n 032 \n \0 \0 \0 \r I H D R 0000020.
I thought this command tells me the type of the file but I'm curious about what the number 0000000 and 211 means. Can anybody please help?
od means "octal dump" (analogous to the hexdumper hd). It dumps bytes of a file in octal notation.
211 octal is 2 * 82 + 1 * 81 + 1 = 137, so you have a byte of value 137 there.
The 0000000 at the beginning of the line and the 0000020 at the beginning of the next are positions in the file, also in octal. If you remove -N 16 from the call, you'll see a column of monotonously ascending octal numbers on the left side of the octal dump; their purpose is to make it instantly visible which part of a dump you're currently reading.
The parameter
-N 16
means to read only the first 16 bytes of filename.png, and
-c
is a format option that tells od
to print printable characters as characters themselves rather than the octal code, and
to print unprintable characters that have a backslash escape sequence (such as \r or \n) as that escape sequence rather than an octal number.
It is the reason that not all bytes are dumped in octal.
If you want to know the file type of a file, use the file utility:
file filename.png
Side note: You may be interested in the man command, which shows the manual page of (among other things) command line tools. In this particular case,
man od
could have been enlightening.
When I use iconv to convert from UTF16 to UTF8 then all is fine but vice versa it does not work.
I have these files:
a-16.strings: Little-endian UTF-16 Unicode c program text
a-8.strings: UTF-8 Unicode c program text, with very long lines
The text look OK in editor. When I run this:
iconv -f UTF-8 -t UTF-16LE a-8.strings > b-16.strings
Then I get this result:
b-16.strings: data
a-16.strings: Little-endian UTF-16 Unicode c program text
a-8.strings: UTF-8 Unicode c program text, with very long lines
The file utility does not show expected file format and the text does not look good in editor either. Could it be that iconv does not create proper BOM? I run it on MAC command line.
Why is not the b-16 in proper UTF-16LE format? Is there another way of converting utf8 to utf16?
More elaboration is bellow.
$ iconv -f UTF-8 -t UTF-16LE a-8.strings > b-16le-BAD-fromUTF8.strings
$ iconv -f UTF-8 -t UTF-16 a-8.strings > b-16be.strings
$ iconv -f UTF-16 -t UTF-16LE b-16be.strings > b-16le-BAD-fromUTF16BE.strings
$ file *s
a-16.strings: Little-endian UTF-16 Unicode c program text, with very long lines
a-8.strings: UTF-8 Unicode c program text, with very long lines
b-16be.strings: Big-endian UTF-16 Unicode c program text, with very long lines
b-16le-BAD-fromUTF16BE.strings: data
b-16le-BAD-fromUTF8.strings: data
$ od -c a-16.strings | head
0000000 377 376 / \0 * \0 \0 \f 001 E \0 S \0 K \0
$ od -c a-8.strings | head
0000000 / * * * Č ** E S K Y ( J V O
$ od -c b-16be.strings | head
0000000 376 377 \0 / \0 * \0 * \0 * \0 001 \f \0 E
$ od -c b-16le-BAD-fromUTF16BE.strings | head
0000000 / \0 * \0 * \0 * \0 \0 \f 001 E \0 S \0
$ od -c b-16le-BAD-fromUTF8.strings | head
0000000 / \0 * \0 * \0 * \0 \0 \f 001 E \0 S \0
It is clear the BOM is missing whenever I run conversion to UTF-16LE.
Any help on this?
UTF-16LE tells iconv to generate little-endian UTF-16 without a BOM (Byte Order Mark). Apparently it assumes that since you specified LE, the BOM isn't necessary.
UTF-16 tells it to generate UTF-16 text (in the local machine's byte order) with a BOM.
If you're on a little-endian machine, I don't see a way to tell iconv to generate big-endian UTF-16 with a BOM, but I might just be missing something.
I find that the file command doesn't recognize UTF-16 text without a BOM, and your editor might not either. But if you run iconv -f UTF-16LE -t UTF_8 b-16 strings, you should get a valid UTF-8 version of the original file.
Try running od -c on the files to see their actual contents.
UPDATE :
It looks like you're on a big-endian machine (x86 is little-endian), and you're trying to generate a little-endian UTF-16 file with a BOM. Is that correct? As far as I can tell, iconv won't do that directly. But this should work:
( printf "\xff\xfe" ; iconv -f utf-8 -t utf-16le UTF-8-FILE ) > UTF-16-FILE
The behavior of the printf might depend on your locale settings; I have LANG=en_US.UTF-8.
(Can anyone suggest a more elegant solution?)
Another workaround, if you know the endianness of the output produced by -t utf-16:
iconv -f utf-8 -t utf-16 UTF-8-FILE | dd conv=swab 2>/dev/null
I first convert to UTF-16, which will prepend a byte-order mark, if necessary as Keith Thompson mentions. Then since UTF-16 doesn't define endianness, we must use file to determine whether it's UTF-16BE or UTF-16LE. Finally, we can convert to UTF-16LE.
iconv -f utf-8 -t utf-16 UTF-8-FILE > UTF-16-UNKNOWN-ENDIANNESS-FILE
FILE_ENCODING="$( file --brief --mime-encoding UTF-16-UNKNOWN-ENDIANNESS-FILE )"
iconv -f "$FILE_ENCODING" -t UTF-16LE UTF-16-UNKNOWN-ENDIANNESS-FILE > UTF-16-FILE
This may not be an elegant solution but I found a manual way to ensure correct conversion for my problem which I believe is similar to the subject of this thread.
The Problem:
I got a text datafile from a user and I was going to process it on Linux (specifically, Ubuntu) using shell script (tokenization, splitting, etc.). Let's call the file myfile.txt. The first indication that I got that something was amiss was that the tokenization was not working. So I was not surprised when I ran the file command on myfile.txt and got the following
$ file myfile.txt
myfile.txt: Little-endian UTF-16 Unicode text, with very long lines, with CRLF line terminators
If the file was compliant, here is what should have been the conversation:
$ file myfile.txt
myfile.txt: ASCII text, with very long lines
The Solution:
To make the datafile compliant, below are the 3 manual steps that I found to work after some trial and error with other steps.
First convert to Big Endian at the same encoding via vi (or vim). vi myfile.txt. In vi do :set fileencoding=UTF-16BE then write out the file. You may have to force it with :!wq.
vi myfile.txt (which should now be in utf-16BE). In vi do :set fileencoding=ASCII then write out the file. Again, you may have to force the write with !wq.
Run dos2unix converter: d2u myfile.txt. If you now run file myfile.txt you should now see an output or something more familiar and assuring like:
myfile.txt: ASCII text, with very long lines
That's it. That's what worked for me, and I was then able to run my processing bash shell script of myfile.txt. I found that I cannot skip Step 2. That is, in this case I cannot skip directly to Step 3. Hopefully you can find this info useful; hopefully someone can automate it perhaps via sed or the like. Cheers.
It seems it is appending a (char)10 to the end of the file. Note that I am doing this in Nautilus, not programmatically. Why does this happen? How to prevent it?
ASCII 0x0A is the newline '\n'.
If that file of yours has been created with echo 1 >file there's a newline added to it. If you're looking to skip that behavior, do echo -n 1 >file.
The ASCII character with the decimal code 10 (0x0a in hex) is '\n' i.e. the new line (LF - Line Feed) character in Unix-like systems. How did you create the file?
EDIT:
If you use echo, you should probably try the -n flag which suppresses the final newline that is emitted by default:
echo -n X > file