The header line is distinguished by having the first 6 characters ``begin '' (the word ``begin'' followed by a space). ``begin '' is followed by a mode (in octal), and a string which names the remote file. Spaces separate the three items in the header line.
The body consists of a number of lines, each at most 62 characters long (including the trailing newline). These consist of a character count, followed by encoded characters, followed by a newline. The character count is a single printing character, and represents the number of bytes that the rest of the line contains. Such integers are always in the range from 0 to 63 and can be determined by subtracting an ASCII space (octal 40) from the character count.
Groups of 3 bytes are stored in 4 characters, 6 bits per character. All are offset by a space to make the characters printable. The last line may be shorter than the usual 45 bytes. If the size is not a multiple of 3, this fact can be determined by the value of the count on the last line. Extra characters will be included to make the character count a multiple of 4. The body is terminated by a line with a count of zero. This line consists of one ASCII space.
The trailer line consists of the word ``end'' on a line by itself.