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like grep but for code: fast and syntax-aware semantic code pattern search for many languages

Project description


Homebrew r2c Community Slack

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:


Language support:

Python Javascript Go       Java   C         Typescript PHP    
Coming... Coming...

Example patterns:

Pattern Matches
$X == $X if ( == ...
requests.get(..., verify=False, ...) requests.get(url, timeout=3, verify=False)
os.system(...) from os import system; system('echo semgrep')
$ELEMENT.innerHTML el.innerHTML = "<img src='x' onerror='alert(`XSS`)'>";
$TOKEN.SignedString([]byte("...")) ss, err := token.SignedString([]byte("HARDCODED KEY"))

see more example patterns in the semgrep-rules repository


Install semgrep with Docker:

docker pull returntocorp/semgrep

On OSX, binaries are available via Homebrew:

brew install returntocorp/semgrep/semgrep

On Ubuntu, an install script is available here


Example Usage

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

def get_node(node_id, nodes):
    for node in nodes:
        if ==  # 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:

$ docker run --rm -v "${PWD}:/home/repo" returntocorp/semgrep --lang python --pattern '$X == $X'
rule:python.deadcode.eqeq-is-bad: useless comparison operation ` ==` or ` !=`.
3:        if ==  # Oops, supposed to be 'node_id'

r2c-developed Rules

You can use rules developed by r2c to search for issues in your codebase:

cd /path/to/code
docker run --rm -v "${PWD}:/home/repo" returntocorp/semgrep --config r2c

Custom Rules

You can also create your own rules:

cd /path/to/code
docker run --rm -v "${PWD}:/home/repo" returntocorp/semgrep --generate-config
docker run --rm -v "${PWD}:/home/repo" returntocorp/semgrep


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:

docker run --rm -v "${PWD}:/home/repo" returntocorp/semgrep --lang javascript --pattern 'eval(...)' path/to/file.js

To fine-tune your searching, specify the --help flag:

docker run --rm returntocorp/semgrep --help

Configuration Files

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.

Pattern Features

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.

Composing Patterns

You can also construct rules by composing multiple patterns together.

Let's consider an example:

  - id: open-never-closed
      - pattern: $FILE = open(...)
      - pattern-not-inside: |
          $FILE = open(...)
    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

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.

docker run --rm -v "${PWD}:/home/repo" returntocorp/semgrep --config r2c



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.

Commercial Support

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!

Project details

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Files for semgrep, version 0.6.0
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