Shell Security Problems

TODO: Link to good resources on the web.

• rm -f * -- a file named '-r' can be interpreted as a flag

• globbing happens after variable expansion. code as data

• escaping from generating programs (shell, HTML, what else?)

• bash shellshock: this was storing code in environment variables. code as data is an anti-pattern.

Examples

• Untrusted git branch name in prompt

• https://news.ycombinator.com/item?id=14987853

Pedantic Style

Motivation for Oil: get rid of pedantic style. The simple code should be correct, not be riddled with subtle bugs.

ShellCheck enforces pedantic style. Modernish developers a new pedantic style.

• double quote everything (except it's not necessary for RHS of assignment)
• add -- after everything, e.g. cd -- $dir not cd $dir. Except echo and others which don't support it.