Write a string to an output stream.
WriteString["file", "string"]
WriteString[channel, "string"]
WriteString[channel, expr1, expr2, …]
WriteString["stdout", "hello world\n"]
→ hello world
NullWriteString[$StandardOutputStream, "hello world\n"]
→ hello world
NullWriteString[$StandardErrorStream, "oh no\n"]' 2> /dev/null
→ NullWriteString[$StandardOutputStream, "a", "b", "c\n"]
→ abc
Null