Joern provides an interactive shell for code analysis, much like an operating system shell. We base this shell on scala-repl-pp which is an extension of the stock Scala repl. In summary, the shell offers the following major features:

• Tab-completion
• GNU readline support for line editing
• Pipe operators (#>, #>>, #| etc)
• Results browsing with a pager
• Add dependencies with maven coordinates
• Server mode
• Structured output rendering including product labels and type information

Launching the Interactive Shell #

The shell can be started by issuing the following command:

$ joern

Basic Keyboard Commands #

The Joern underlying shell is essentially an interactive Scala shell that supports the following keyboard commands:

Exporting Results with Pipe Operators and toJson #

Inspired by unix shell redirection and pipe operators (>, >> and |) you can redirect output into files with #> (overrides existing file) and #>> (create or append to file), and use #| to pipe the output to an external command:

// write results to file (first overrides, seconds appends)
cpg.method.name #> "/tmp/foo.txt"
cpg.method.name #>> "/tmp/foo.txt"

// render methods as json, then export to file
cpg.method.toJson #> "/tmp/foo.json"

// pipe results to external command
cpg.method.name #| "cat" 

// same as above, but make that command inherit stdin/stdout
// this is what happens internally if you run `cpg.method.name.browse`
cpg.method.name #|^ "less"

Inline Code Browsing #

For an increasing number of languages, the Joern shell allows you to read code associated with query results directly on the shell. For example, to review all calls to memcpy, you can issue:

joern> cpg.method.name("memcpy").callIn.code.l

res5: List[String] = List(
  "memcpy(buf, first, first_len)",
  "memcpy(buf + first_len, second, second_len)",
  "memcpy(buf, first, first_len)",
  "memcpy(buf + first_len, second, second_len)",
  "memcpy(buf + first_len, second, second_len)",
  "memcpy(buf, first, first_len)"
)

You can also pipe the result list into a pager (less) as follows:

joern> cpg.method.name("memcpy").callIn.code.browse

To study the context in which a result occurs, you can use the .dump method, which will dump the enclosing function’s code for each finding, and point you to the finding via an arrow:

joern> cpg.method.name("memcpy").callIn.dump

int main() {
  unsigned int first_len = UINT_MAX - 256;
  unsigned int second_len = 256;
  unsigned int buf_len = 256;

  char first[first_len], second[second_len], buf[buf_len];
  int new_len = (first_len+second_len); // <- IDB (negative)

  if(new_len <= 256) {
	memcpy(buf, first, first_len);
        memcpy(buf + first_len, second, second_len); /* <=== */
  }
}

...

You can use this feature together with browse to read code in the pager. Finally, if you want to read the code in your editor of choice, just dump it to a file:

cpg.method.name("memcpy").callIn.dumpRaw #> "/tmp/foo.c"

We use dumpRaw here to skip syntax highlighting, as your editor will most likely do that for you.

Please make sure source-highlight is installed for the .dump feature to work.

Dynamically Importing Additional Scripts #

You can dynamically load additional scripts at any time.

As an example, let’s assume there’s a file called MyScript.sc that contains only val elite = 31337. You can import the script as follows:

//> using file MyScript.sc

> importing /home/mp/Projects/shiftleft/joern/./MyScript.sc (1 lines)
val elite: Int = 31337

You can specify the filename with relative or absolute paths:

//> using file scripts/MyScript.sc
//> using file ../MyScript.sc
//> using file /path/to/MyScript.sc

Adding Dependencies to the JVM classpath on startup #

Note: this used to also work dynamically (i.e. add dependencies to a running repl), but as of joern 2.0.0 all dependencies must be known at startup.

Option 1: via --dep parameter

./joern --dep com.michaelpollmeier:versionsort:1.0.7
joern> versionsort.VersionHelper.compare("1.0", "0.9")
val res0: Int = 1

To add multiple dependencies, you can specify this parameter multiple times.

Option 2: use the //> using dep directive in an imported script:

echo '//> using dep com.michaelpollmeier:versionsort:1.0.7' > predef.sc
./joern --import predef.sc

joern> versionsort.VersionHelper.compare("1.0", "0.9")
val res0: Int = 1

For Scala dependencies use :::

./joern --dep com.michaelpollmeier::colordiff:0.36
colordiff.ColorDiff(List("a", "b"), List("a", "bb"))
// color coded diff

Additional dependency resolvers and credentials #

If your dependencies are not hosted on maven central, you can specify additional resolvers - including those that require authentication:

Option 1: via --repo parameter on startup:

./joern --repo "https://repo.gradle.org/gradle/libs-releases" --dep org.gradle:gradle-tooling-api:7.6.1
org.gradle.tooling.GradleConnector.newConnector()

To add multiple dependency resolvers, you can specify this parameter multiple times.

Or via //> using resolver directive as part of a script:

script-with-resolver.sc

//> using resolver https://repo.gradle.org/gradle/libs-releases
//> using dep org.gradle:gradle-tooling-api:7.6.1
println(org.gradle.tooling.GradleConnector.newConnector())

./joern --script script-with-resolver.sc

If one or multiple of your resolvers require authentication, you can configure your username/passwords in a credentials.properties file:

mycorp.realm=Artifactory Realm
mycorp.host=shiftleft.jfrog.io
mycorp.username=michael
mycorp.password=secret

otherone.username=j
otherone.password=imj
otherone.host=nexus.other.com

The prefix is arbitrary and is only used to specify several credentials in a single file. joern uses coursier to resolve dependencies.

Measuring the Time While Running a Computation #

time { 
  println("long running computation")
  Thread.sleep(1000)
  42
}
// res: (42, 1000332390 nanoseconds)