How do I convert a file from DOS format to UNIX format (remove CRs from CR-LF line terminators)?

Carriage return characters (CRs) are used in line ending markers on some systems. There are three different kinds of line endings in common use:

• Unix systems use Line Feeds (LFs) only.
• MS-DOS and Windows systems use CR-LF pairs.
• Old Macintosh systems use CRs only.

If you're running a script on a Unix system, the line endings need to be Unix ones (LFs only), or you will have problems. You can check the kind of line endings in use by running:

cat -e yourscript

If you see something like this:

command^M$
^M$
another command^M$

then you need to remove the CRs. There are a plethora of ways to do this.

To remove them from a file, ex is a good standard way to do it:

ex -sc $'%s/\r$//e|x' file

There are many more ways:

• Some systems have a dos2unix command which can do this. Or recode, or fromdos.

• You can also use col <input.txt > output.txt

• In vim, you can use :set fileformat=unix to do it and save it with a ":w".

• You can use Perl:

  •   perl -pi -e 's/\r\n/\n/' filename

  This has the advantage of overwriting the original file, so you don't have to mess with temporary files.

Another way to check it:

file yourscript

The output tells you whether the ASCII text has some CR, if that's the case. Note: this is only true on GNU/Linux. On other operating systems, the result of file is unpredictable, except that it should contain the word "text" somewhere in the output if the result "kind of looks like a text file of some sort, maybe".

imadev:~$ printf 'DOS\r\nline endings\r\n' > foo
imadev:~$ file foo
foo:            commands text
arc3:~$ file foo
foo: ASCII text, with CRLF line terminators

And another way to fix it:

nano -w yourscript

Type Ctrl-O and before confirming, type Alt-D (DOS) or Alt-M (Mac) to change the format.

And another way to fix it:

dos2unix filename