WriteLine¶

Write a string to an output stream, followed by a newline. It is WriteString plus a line terminator.

The channel is an open stream, a file name, or one of the standard streams "stdout" and "stderr":

$ wo 'WriteLine["stdout", "first"]; WriteLine["stdout", "second"]'
first
second
Null

Writing through a stream opened with OpenWrite appends one line per call, so the file holds the lines in the order they were written:

$ wo 'file = FileNameJoin[{$TemporaryDirectory, "woxi-write-line.txt"}]; stream = OpenWrite[file]; WriteLine[stream, "Some log text"]; WriteLine[stream, "more"]; Close[stream]; ReadList[file, String]'
{Some log text, more}

A file name starting with ! writes into an external command's standard input, the same as for WriteString:

$ wo 'stream = OpenWrite["!tr a-z A-Z"]; WriteLine[stream, "hello pipe"]; Close[stream];'
HELLO PIPE
Null