Scanning Shell Scripts With Semgrep

Semgrep has introduced experimental support for Bash scripting, allowing users to write rules that identify common shell syntax errors and unsafe command usage. This tool is particularly effective in situations where traditional grep falls short, such as detecting forbidden command calls, preventing unintended variable splitting due to the IFS variable, and catching unquoted variable expansions that could lead to whitespace splitting. Semgrep uses unique pattern syntax, including metavariables and ellipses, to identify specific shell constructs, though users should be aware of potential complications with YAML syntax and the experimental nature of the Bash support, which may not yet cover all possible Bash constructs. Despite these limitations, Semgrep successfully parses a significant portion of Bash/sh code and effectively searches for simple commands, pipelines, and variable expansions, among other constructs, providing a powerful tool for enhancing shell script reliability and security.