Tuesday, June 22, 2010

Convert Line Endings with Aplomb

When transferring files from system to system, for instance, using csv files to transfer data from one db to another, sometimes there are problems where programs will not process a file because of its line endings. This happens especially if you process a file on one platform, say Mac, and try to use the file on another, say Windows. Even if you have saved a file as CSV from Mac Excel 2008, it will not necessarily be saved in a format that can be read programmatically, if the program is expecting a certain type of line ending.

How Can We Avoid Line Terminator Problems and Troubles?

Let's recall how lines are terminated by default on Windows, Mac and Unix.

  • Windows-style line endings are CRLF ( \r\n or hex 0D0A )
  • Mac-style line endings are CR ( \r or hex 0D )
  • Unix-style line endings are LF ( \n or hex 0A )

There are a number of ready-made command line programs like unix2dos, dos2unix, mac2dos, dos2mac and so on, that can be used to convert line endings. Note that you can also use the tr or perl commands as well. Tr is available on Macs by default and on almost any unix. Perl is pretty ubiquitous as well. E.g:

[root@server /path/to/files]# tr '\r' '\r\n' win-crlf-file.csv

[root@server /path/to/files]# tr '\n' '\r\n' win-crlf-file.csv

[root@server /path/to/files]# perl -pe 's/\r\n|\n|\r/\r\n/g' unix-lf-file.csv > win-crlf-file.csv

If you want to find out whether a file has the expected line terminators, you can use the file command on *nix or Mac. Here's what that looks like:

[root@server /path/to/files]# file inputfile1.csv

inputfile1.csv: ASCII text, with CRLF line terminators

[root@server /path/to/files]# file inputfile2.csv

inputfile2.csv: ASCII text, with CR line terminators

You can also use the cat command to show line endings, with its -e switch. Do a man cat for more info, because you can also get line numbers, for instance. The first file below has CRLF, which shows up in cat’s output as ^M$, and the second file has only a ^, which is equivalent to the Mac CR line ending only situation. What you need will depend upon the import program.

[root@server /path/to/files]# cat -e inputfile1.csv


123-ABC-456,CUST000001,100,6-01-2010,05-31-2011,Regular Update^M$

456-ABC-789,CUST000001,100,6-01-2010,05-31-2011,Regular Update^M$

[root@server /path/to/files]# cat -e inputfile2.csv

Part,Cust,Price,StartDate,EndDate,Reason^123-ABC-456,CUST000001,100,01-06-2010,31-05-2011,Regular Update^

Besides line endings, there is also the text encoding of the file, to watch out for. For instance, is the file saved in Roman or Unicode or some other format? In the end, take care to confirm the file you have output is what is needed by the program for input. Enjoy!

1 comment:

drf5n said...

New mac line endings are the unix-like \013 (LF) character, but Excel writes \015 (CR) which don't parse well on Mac OSX machines.

Also, 'tr' just does a character by character transliteration, so it won't replace a '\r' with a two-character '\r\n', it will just try to replace \r with \r and ignore the \n.

Thirdly, perl expands "\n" into the local machine's native line ending, so "\r\n" doesn't mean "\012\015" on all platforms.

try this on your mac:

echo -e "one\n\two" > junk

tr '\n' '\r' junkCR

tr '\n' '\r\n' junkCRLF

echo -e "one\r\ntwo\r" > junkCRLF2

file junk*

junk: ASCII text

junkCR: ASCII text, with CR line terminators

junkCRLF: ASCII text, with CR line terminators

junkCRLF2: ASCII text, with CRLF line terminators