diff -Naur passwd.old passwd.new > passwd.patch (N: new file a: text, u: unified; r: recursive)
cat passwd.patch
patch -p0 < passwd.patch # 更新passwd.old
patch -R -p0 < passwd.patch # 还原passwd.old
diff -Naur passwd.old passwd.new > passwd.patch (N: new file a: text, u: unified; r: recursive)
cat passwd.patch
patch -p0 < passwd.patch # 更新passwd.old
patch -R -p0 < passwd.patch # 还原passwd.old