snakemake get environment variable for rule name and log path

Question

When a rule fails in snakemake workflow, it returns a descriptive message in log file like following:

Error in rule step1:
    jobid: 99
    output: results/foo/step1/sample5/outdir/output1.tsv, results/foo/step1/sample5/outdir/output2.tsv
    log: logs/step1/sample5_out.log (check log file(s) for error message)
    shell:
    ...
        (exited with non-zero exit code)

Since I run workflow over many samples, I have defined a postrun.sh bash script in jobscript.sh directive that runs after snakemake {exec_job} section and notifies me via userbot in slack channel when a step failed for one or more samples.

jobscript.sh

        ########################### START SNAKEMAKE CMD ############################
    {exec_job}
        ############################ END SNAKEMAKE CMD #############################
    exitstat=$?
    export exitstat

    echo "END at $(date)"
. "${{HOME}}"/.smk_confs/postrun.sh

postrun.sh

## execute after running each of snakemake job
echo 'Running postrun.sh'
ERRMSG="MYJOB ID: $PBS_JOBID failed at $(pwd) on $(hostname) for ${USER} with exit status: ${exitstat}."

## ping to slack
ping_slack -m "$ERRMSG"
sleep 5

I am looking for a snakemake exported environment variable that I can use in postrun.sh to know which rule ID failed for one or more samples. For now, I can think of using job scheduler variable matching job name, e.g, PBS_JOBNAME, but better if I have a variable from snakemake API for rule ID or preferably, path to log file.

Thanks

Answer 1

You could add an exit trap to the beginning of the shell scripts inside your Snakefile, which is executed after each script is done and sends a message when there was an error:

 shell:
    """
    trap 'if [ $? -neq 0 ]; then ping_slack -m "Error in rule xxx with input {input}"; exit 1' EXIT
    ...