What happens when "\r\n" is used in a mac OS X?
In Windows, it goes to the next line; but this can be done just with the '\n' in Mac OS X. What would happen if "\r\n" is used in a mac os x.
It depends on where you use the \r\n
Text files: Modern text editors can automatically detect the line endings and display the content of the lines without any abnormal behaviour. They may additionally notify that the line endings are in DOS format somewhere in their notification/message bar
I am not sure about the default text editor included in Max OSX, but any text editor not capable of automatically detecting the type of line endings would show an additional character to represent the \r at the end of the lines
Based on the capability of the text editor, these may be displayed as tiny opaque boxes with or without a 'CR' inside of them
Shell scripts: If the text files are actually used for shell scripting, then the additional \r will cause the scripts to fail with errors
dos2unix or d2u can convert the files from DOS format (\r\n) to unix format (\n) line endings
Side note, older versions of mac used \r for line endings
Related
This question already has answers here:
What does the ^M character mean in Vim?
(15 answers)
Closed 2 years ago.
I'm new to Linux sorry if my question sounds dumb.
We know that Linux and Mac OS X use \n (0xa), which is the ASCII line feed (LF) character. MS Windows and Internet protocols such as HTTP use the sequence \r\n (0xd 0xa). If you create a file foo.txt in Windows and then view it in a Linux text editor, you’ll see an annoying ^M at the end of each line, which is how Linux tools display the CR character.
Bu why Linux tools display the CR character as ^M? as my understanding is, \r (carriage return) is to move the cursor in the beginning of the current line, so the sensible approach to display it is like, when you open the file, you see the cursor is in the beginning of the line(that contains \r), so ^M shouldn't be displayed?
PS: some people post answers that how to remove ^M, but I wnat to know why eventually^M is displayed rather than moving the cursor in the beginning, which is the definition of carriage return.
The ASCII control characters like TAB, CR, NL and others are intended to control the printing position of a teletypewriter-like display device.
A text editor isn't such a device. It is not appropriate for a text editor to treat a CR character literally as meaning "go to the first column"; it would make a confusing gibberish out of the editing experience.
A text editor works by parsing a text file's representation, to create an internal representation which is presented to the user. On Unix-like operating systems, a file is represented by zero or more lines, which are terminated by the ASCII NL character. Any CR characters that occur just look like part of the data, and not part of the line separation.
Not all editors behave the same way. For instance, the Vim editor will detect that a file uses CR-LF line endings, and load it properly using that representation. A flag is set for that buffer which indicates that it's a "DOS" file, so that when you save it, the same representation is reproduced.
That said, there is a feature in the actual Linux kernel for representing control characters like CR using the ^M notation. The TTY line discipline for any given TTY device can be configured to print characters in this notation, but only when echoing back the characters received.
Demo:
$ stty echoctl # turn on notational echo of control characters
$ cat # run some non-interactive program with rudimentary line input
^F^F^F^F^F^F
^C
$
Above, the Ctrl-F that I entered was echoed back as ^F. So, in fact there is a "Linux editor" which uses this notation: the rudimentary line editor of the "canonical input mode" line discipline.
I'm trying to send file using curl to an endpoint and save the file to the machine.
Sending curl from Linux and saving it on the machine works well,
but doing the same curl from Windows is adding ^M character to every end of line.
I'm printing the file before saving it and can't see ^M. Only viewing the file on the remote machine after saving it shows me ^M.
A simple string replacement doesn't seem to work.
Why is ^M being added? How can I prevent this?
Quick Answer: That's a carriage return. They're a harmless but mildly irritating artifact of how Windows encodes text files. You can strip them out of your files with dos2unix. You can configure most text editors to use "Unix Line Endings" or "LF Line Endings" to prevent them from appearing in new files that you create from Windows PCs in the future.
Long Answer (with some historical trivia):
In a plain text file, when you create a new line (by pressing enter/return), a "line break" is embedded in the file. On Unix/Linux, this is a single character, '\n', the "line feed". On Windows, this is two sequential characters, '\r\n', the "carriage return" followed by the "line feed".
When physical teletype terminals, which behaved much like typewriters, were still in use, the "line feed" character meant "move the paper up to the next line" and the "carriage return" character meant "slide the carriage all the way over so the typing head is on the far left". From the very beginning, nearly all teletype terminals supported implicit carriage return; i.e., triggering a line feed would automatically trigger a carriage return. The developers working on what later evolved into Windows decided that it would be best to include explicit carriage returns, just in case (for some reason) the teletype does not perform one implicitly. The Unix developers, on the other hand, chose to work with the assumption of implicit carriage return.
The carriage return and line feed are ASCII Control Characters which means they do not have a visible representation as standalone printable characters, instead they affect the output cursor itself (in this case, the position of the output cursor).
The "^M" you see is a stand-in representation for the carriage return character, used by programs that don't fully "cook" their output (i.e., don't apply the effects of some ASCII Control Characters). (Other control characters have other representations starting with "^", and the "^" character is also used to represent the "ctrl" keyboard key in some Unix programs like nano.)
You can use dos2unix to convert the line endings from Windows-style to Unix-style.
$ curl https://example.com/file_with_crlf.txt | dos2unix > file.txt
On some distros, this tool is included by default, on others it can be installed via the package manager (e.g., on Ubuntu, sudo apt install dos2unix). There also exists a package, unix2dos, for the inverse.
Most "smart" text editors for coding (Sublime, Atom, VS Code, Notepad++, etc.) will happily read and write with either Windows-style or Unix-style line endings (this might require changing some configuration options). Often, the line-endings are auto-detected by scanning the contents of a file, and usually new files are created with the Operating System's native line endings (by default). Even the new version of Notepad supports Unix-style line endings. On the other hand, some Unix tools will produce strange results in the presence of Windows-style line breaks. If your codebase will be used by people on both Unix and Windows operating systems, the nice thing to do is to use Unix-style line endings everywhere.
Git on Windows also has an optional mode that checks out all files with Windows-style line breaks, but checks them back in with Unix-style line breaks.
Side Notes (interesting, but not directly related to your question):
What the carriage return actually does (on a modern virtual terminal, be it Windows or Unix) is move the output cursor to the beginning of the line. If you use the carriage return without a line feed, you can "overwrite" part of a string that has already been printed.
$ printf "dogdog" ; printf "\rcat\n"
catdog
Some Unix programs use this to asynchronously update part of the last line of output, to implement things like a live-updating progress indicator. For example, curl, which shows download progress on stdout if the file contents are piped elsewhere.
Also: If you had a tool that interpreted Windows-style line endings as literally as possible, and you fed it a string with Unix-style line endings such as "hello\nworld", you would get output like this:
hello
world
Fortunately, such implementations are extremely rare and, in general, the vast majority of Windows tools can render Unix-style line-endings identically to Windows-style line endings without any problem.
I am exporting data in a csv file using ssis. In my ssis package i compress the file in zip format and upload it on a linux server using sftp. The problem is that in the destination file system, the csv files include a ^M character which comes from the dos system.
I found three solutions.
First i could set the sftp transfer mode to ascii and not zip the file (i later found out this is only supported by ftp). Considering that my unzipped file is > 3Gb that is not efficient, the upload will take ages.
Secondly once transferred i could unzip the file and convert it using dos2unix utility, but again dos2unix is not installed and i am not authorized to install it to the target system.
Finally i could use a unix editor like sed to remove ^M from the end of lines. My file is consisted of more than 4 million lines and this would again take ages.
Q: Is there any way to preformat my file in ASCII using ssis, then zip and transfer?
While searching on this issue i found a very useful links were they described the cause and possible resolutions of this issue:
How to remove CTRL-M (^M) characters from a file in Linux
Why are special characters such as “carriage return” represented as “^M”?
Cause
File has been transferred between systems of different types with different newline conventions. For example, Windows-based text editors will have a special carriage return character (CR+LF) at the end of lines to denote a line return or newline, which will be displayed incorrectly in Linux (^M). This can be difficult to spot, as some applications or programs may handle the foreign newline characters properly while others do not. Thus some services may crash or not respond correctly. Often times, this is because the file is created or perhaps even edited on a Microsoft Windows machine and then uploaded or transferred to a Linux server. This typically occurs when a file is transferred from MS-DOS (or MS-Windows) without ASCII or text mode.
Possible resolutions
(1) Using dos2unix command
dos2unix includes utilities to convert text files with DOS or MAC line breaks to Unix line breaks and vice versa. It also includes conversion of UTF-16 to UTF-8.
dos2unix
Dos2Unix / Unix2Dos - Text file format converters
dos2unix and unix2dos commands
You can use a similar command via Execute Process Task:
dos2unix filename
(2) Data Flow Task
You can create a Data Flow task that transfer data from Flat File Source into a new Flat File Destination were both Flat File Connection mAnager has the same structure except the Row Delimiter property ({CR}{LF} in Source , {LF} in destination)
Flat File Connection Manager Editor (Columns Page)
(3) Using a Script Task - StreamReader/Writer
You can use a script task with a similar code:
string data = null;
//Open and read the file
using (StreamReader srFileName = new StreamReader(FileName))
{
data = srFileName.ReadToEnd();
data = data.Replace("\r\n","\n");
}
using (StreamWriter swFileName = new StreamWriter(FileName))
{
swFileName.Write(data);
}
Replacing LF with CRLF in text file
(4) Extract using unzip -a
From the following unzip documentation:
-a
convert text files. Ordinarily all files are extracted exactly as they are stored (as ''binary'' files). The -a option causes files identified by zip as text files (those with the 't' label in zipinfo listings, rather than 'b') to be automatically extracted as such, converting line endings, end-of-file characters and the character set itself as necessary. (For example, Unix files use line feeds (LFs) for end-of-line (EOL) and have no end-of-file (EOF) marker; Macintoshes use carriage returns (CRs) for EOLs; and most PC operating systems use CR+LF for EOLs and control-Z for EOF. In addition, IBM mainframes and the Michigan Terminal System use EBCDIC rather than the more common ASCII character set, and NT supports Unicode.) Note that zip's identification of text files is by no means perfect; some ''text'' files may actually be binary and vice versa. unzip therefore prints ''[text]'' or ''[binary]'' as a visual check for each file it extracts when using the -a option. The -aa option forces all files to be extracted as text, regardless of the supposed file type. On VMS, see also -S.
So you can use the following command to extract text files with changing line endings:
unzip -a filename
Credit to #jww comment
Other Useful links
How to Remove ^M in Linux & Unix
Remove CTRL-M characters from a file in UNIX
Convert DOS line endings to Linux line endings in vim
How to replace crlf with lf in a single file
How to remove Windows carriage returns for text files in Linux
I didn't try it, but I thought you could do a CR+LF -> LF conversion just when outputing to the csv file. I looked in this link here
Scroll down to the section "Header row delimiter". It seems that if you choose {LF} as a row delimiter, your resulting .zip file will show correctly in your linux box.
BTW, probably you know, but I have to mention that ^M is the representation of CR in a linux / unix box.
BTW2, in most cases the ^M in linux is not a problem, just some annoying thing.
I hope I could help!
I develop and use Git on both Windows and Linux. When using IDEs or Git on Windows, I'm frequently prompted on whether to save files with CR LF or not.
I am doing mainly C# and JavaScript ES6 development which involves code that contains multi-line strings.
What reasons are there to save files with CR LF on Windows? Are CR-LFs mostly of historical significance? I have not yet noticed a drawback to working with UNIX \n line endings on Windows.
Windows batch files can malfunction when saved with newline endings because the goto command works by jumping to the appropriate offset in the script — but it is not computed correctly unless the lines end with carriage-return/line-feed.
Some Windows programs don't properly handle '\n' without '\r' but any decent editor or for that matter any decent program should handle them identically. But CRLF is traditionally the sanctioned way to do line endings on Windows and you might have compatibility issues if you don't.
We have two machines (unix and windows) and we send a file vía FTP from first (unix [IBM1047]) to second (windows [UTF16]). If you use ASCII mode, some especial characters such as Ñ ó... are not display correctly. So we changed to BINARY mode and after the transfer we set charset file to UTF16. But everything works fine except returns carriages which are not displayed (1 line un the file).
So what is we missing?
Binary mode means that there are no changes done to the file, which includes changes on the line endings. UNIX and Windows have traditionally different line endings, i.e. \n on UNIX vs. \r\n on Windows. If your application is not able to deal with UNIX-style line endings you have to convert all the line endings in the file. See also Windows command to convert Unix line endings?.