0. check
cat -A file.txt
1. dos2unix
sudo apt-get install dos2unix
dos2unix file.txt
2. sed
sed -i 's/\r$//' file.txt
sed -i.bak 's/\r$//' file.txt
sed -i $'s/\r$//' file.txt # DOS to Unix
sed -i $'s/$/\r/' file.txt # Unix to DOS
sed -i 's/^M$//' file.txt # DOS to Unix
sed -i 's/$/^M/' file.txt # Unix to DOS
3. tr
tr -d "\r" < file
tr -d '\015' <DOS-file >UNIX-file
4. vim
vim file.txt -c "set ff=unix" -c ":wq"
5. awk
awk '{ sub("\r$", ""); print }' dos.txt > unix.txt
6. perl
perl -pe 's/\r$//' < dos.txt > unix.txt
7. ex
ex -bsc '%!awk "{sub(/\r/,\"\")}1"' -cx file