That's WordPress default behavior. It also changes simple and double quotes.

The simplest fix is to enclose your command lines with the "<code>" HTML tag.

A good WordPress companion for blog featuring lots of command-lines and code is Alex Gorbatchev's SyntaxHighlighter: http://alexgorbatchev.com/SyntaxHighlighter . Several WordPress plugins are available. I personally use SyntaxHighlighter Evolved: http://wordpress.org/extend/plugins/syntaxhighlighter