rules:
  - id: unquoted-variable-expansion-in-command
    languages: [bash]
    severity: INFO
    message: >-
      Variable expansions must be double-quoted so as to prevent
      being split into multiple pieces according to whitespace or
      whichever separator is specified by the IFS variable.
      If you really wish to split the variable's contents,
      you may use a variable that starts with an underscore e.g.
      $_X instead of $X, and semgrep will ignore it. If what you need
      is an array, consider using a proper bash array.
    metadata:
      category: correctness
      technology:
        - bash
    patterns:
      - pattern-either:
          # This is subtle (and not great): ...${$VAR}... is a concatenation,
          # which is interpreted as concatenate(..., expand($VAR), ...)
          # and won't match a simple variable expansion.
          # This is why we need two patterns below.
          - pattern: |
              ... ${$VAR} ...
          - pattern: |
              ... ...${$VAR}... ...
      - metavariable-regex:
          metavariable:
            $VAR
            # generally safe: $# $? $$ $! $-
            # unsafe: $* $@ $0 $15 $_ $foo $FOO
            # unsafe but tolerated: $_foo $_FOO $_42
          regex: "[*@0-9]|[A-Za-z].*"

  - id: unquoted-command-substitution-in-command
    languages: [bash]
    severity: INFO
    message: >-
      The result of command substitution $(...) or `...`, if unquoted,
      is split on whitespace or other separators specified by the IFS
      variable. You should surround it with double quotes to avoid
      splitting the result.
    metadata:
      category: correctness
      technology:
        - bash
    patterns:
      - pattern-either:
          - pattern: |
              ... $(...) ...
          - pattern: |
              ... ...$(...)... ...
      - pattern-regex: |
          .*(\$\([^\(]|`).+([^\)]\)|`).*