Is there a Bash command to convert \r\n to \n?

There is:

dos2unix

There is a Unix utility called conv that can convert line endings. It is often invoked with softlinks to u2d or d2u or unix2dos or dos2unix.

Additionally there are utilities called fromdos and todos.

Translate (tr) is available in all Unixes:

tr -d '\r'  # From \r\n line end (DOS/Windows), the \r will be removed so \n line end (Unix) remains.

With sed and find that end with .txt, .php, .js, .css:

 sed -rie 's/\r\n/\n/' \
 $(find . -type f -iregex ".*\.\(txt\|php\|js\|css\)")

Doing this with POSIX is tricky:

• POSIX Sed does not support \r or \15. Even if it did, the in place option -i is not POSIX

• POSIX Awk does support \r and \15, however the -i inplace option is not POSIX

• d2u and dos2unix are not POSIX utilities, but ex is

• POSIX ex does not support \r, \15, \n or \12

To remove carriage returns:

awk 'BEGIN{RS="\1";ORS="";getline;gsub("\r","");print>ARGV[1]}' file

To add carriage returns:

awk 'BEGIN{RS="\1";ORS="";getline;gsub("\n","\r&");print>ARGV[1]}' file