semgrep is a tool for easily detecting and preventing bugs and anti-patterns in your codebase. It combines the convenience of grep with the correctness of syntactical and semantic search. Developers, DevOps engineers, and security engineers use semgrep to write code with confidence.

Try it now: https://semgrep.live

Language support:

Example patterns:

→ see more example patterns in the semgrep-rules repository

On macOS, binaries are available via Homebrew:

brew install returntocorp/semgrep/semgrep

On Ubuntu, an install script is available on each release here

./semgrep-v0.6.1-ubuntu-generic.sh

To try semgrep without installation, you can also run it via Docker:

docker run --rm -v "${PWD}:/home/repo" returntocorp/semgrep --help

Here is a simple Python example, test.py. We want to retrieve an object by ID:

def get_node(node_id, nodes):
    for node in nodes:
        if node.id == node.id:  # Oops, supposed to be 'node_id'
            return node
    return None

This is a bug. Let's use semgrep to find bugs like it, using a simple search pattern: $X == $X. It will find all places in our code where the left- and right-hand sides of a comparison are the same expression:

$ semgrep --lang python --pattern '$X == $X' test.py
test.py
3:        if node.id == node.id:  # Oops, supposed to be 'node_id'

For simple patterns use the --lang and --pattern flags. This mode of operation is useful for quickly iterating on a pattern on a single file or folder:

semgrep --lang javascript --pattern 'eval(...)' path/to/file.js

For advanced configuration use the --config flag. This flag automagically handles a multitude of input configuration types:

• --config <file|folder|yaml_url|tarball_url|registy_name>

In the absence of this flag, a default configuration is loaded from .semgrep.yml or multiple files matching .semgrep/**/*.yml.

semgrep patterns make use of two primary features:

• Metavariables like $X, $WIDGET, or $USERS_2. Metavariable names can only contain uppercase characters, or _, or digits, and must start with an uppercase character or _ - names like $x or $some_value are invalid. Metavariables are used to track a variable across a specific code scope.
• The ... (ellipsis) operator. The ellipsis operator abstracts away sequences so you don't have to sweat the details of a particular code pattern.

For example,

$FILE = open(...)

will find all occurrences in your code where the result of an open() call is assigned to a variable.

You can also construct rules by composing multiple patterns together.

Let's consider an example:

rules:
  - id: open-never-closed
    patterns:
      - pattern: $FILE = open(...)
      - pattern-not-inside: |
          $FILE = open(...)
          ...
          $FILE.close()
    message: "file object opened without corresponding close"
    languages: [python]
    severity: ERROR

This rule looks for files that are opened but never closed. It accomplishes this by looking for the open(...) pattern and not a following close() pattern. The $FILE metavariable ensures that the same variable name is used in the open and close calls. The ellipsis operator allows for any arguments to be passed to open and any sequence of code statements in-between the open and close calls. We don't care how open is called or what happens up to a close call, we just need to make sure close is called.

For more information on rule fields like patterns and pattern-not-inside see the configuration documentation.

Equivalences are another key concept in semgrep. semgrep automatically searches for code that is semantically equivalent. For example, the following patterns are semantically equivalent. The pattern subprocess.Popen(...) will fire on both.

subprocess.Popen("ls")

from subprocess import Popen as sub_popen

result = sub_popen("ls")

For a full list of semgrep feature support by language see the language matrix.

As mentioned above, you may also specify a registry name as configuration. r2c provides a registry of configuration files. These rules have been tuned on thousands of repositories using our analysis platform.

semgrep --config r2c

• semgrep presentation at HellaSecure and slides
• Pattern features documentation
• Configuration files documentation
• Integrations
• Development
• Bug reports

semgrep is LGPL-licensed, feel free to help out: CONTRIBUTING.

semgrep is a frontend to a larger program analysis library named pfff. pfff began and was open-sourced at Facebook but is now archived. The primary maintainer now works at r2c. semgrep was originally named sgrep and was renamed to avoid collisons with existing projects.

semgrep is proudly supported by r2c. We're hiring!

Interested in a fully-supported, hosted version of semgrep? Drop your email and we'll ping you!