count the number of lines from the current file position to the end of the file
file descriptor or filename
The CountLines(file) command counts the number of lines from the current position in file to the end of file.
A line is defined to be zero or more characters delimited by the current file position, a new line character, and the end of file. There is one exception to this definition: if the last character in the file is a newline, then the null string (zero characters) between this newline and the end of file is not considered a line. This definition is consistent with the behavior of ReadLine and readline.
An error is raised if file is not a valid descriptor or if it is the name of a file that does not exist.
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