Which singularity image is used?

[ManavalanG]

What singularity image is used for this pipeline? Repo's readme says this pipeline can be run with singularity, but I don't see singularity: defined anywhere in the pipeline.

[ManavalanG]

Running a Snakefile without singularity: defined doesn't result in any warning or error. Isn't this a bug?

Snakefile:

rule aa:
    output: 'aa.txt'
    shell: "touch {output}"

Command used and its output:

$ snakemake  --use-singularity
Building DAG of jobs...
Using shell: /bin/bash
Provided cores: 1
Rules claiming more threads will be scaled down.
Job counts:
	count	jobs
	1	aa
	1

[Wed Dec 11 13:28:33 2019]
rule aa:
    output: aa.txt
    jobid: 0

[Wed Dec 11 13:28:33 2019]
Finished job 0.
1 of 1 steps (100%) done