backtick-substitution
A deny rule by default: it refuses a backtick command substitution, which inside double quotes runs a command, and names what to run instead.
What it catches
A backtick command substitution, which inside double quotes runs a command.
Why
Inside double quotes a backtick starts a command substitution, so a pattern or a message carrying a literal backtick runs code: the backtick pairs with the next one anywhere on the line, and everything between them becomes one command. A grep whose pattern and a later stage's pattern each hold a triple backtick pair them into ONE substitution that swallows the file operand and the rest of the pipeline. What is left is a grep with no file, reading a stdin that never closes. A literal backtick belongs in single quotes, where it is text. A substitution is written $(...), which nests and cannot pair with a stray backtick. Backticks inside single quotes and inside a quoted heredoc (<<'EOF') are text and never fire; neither does a line that does not parse.
Default and override
By default this rule takes the decision deny. A workspace sets it by name, in its root
magusfile, to deny, advise or off:
magus\guard.builtins({"backtick-substitution": "advise"})
A loosening takes effect once it is committed; a tightening applies at once.
Seeing it
A verdict names its rule in brackets, which is how you got here:
deny [backtick-substitution]: ...
A workspace that sets this rule to advise sees advise [backtick-substitution]: ... instead.
magus describe rule backtick-substitution prints the same entry at a terminal, and
magus describe rules lists every rule this workspace enforces.
See also
- All rules - what this workspace enforces, deny first
- The guard - how a verdict is reached and wired
- Setting a built-in rule - how a workspace changes this default