params.fastq = "$baseDir/data/fastq/*_{1,2}.fastq" params.index = "$baseDir/data/index/*.index.*" log.info "fastq files : ${params.fastq}" log.info "index files : ${params.index}" Channel .fromFilePairs( params.fastq ) .ifEmpty { error "Cannot find any fastq files matching: ${params.fastq}" } .set { fastq_files } Channel .fromPath( params.index ) .ifEmpty { error "Cannot find any index files matching: ${params.index}" } .set { index_files } process mapping_fastq { tag "$pair_id" cpus 4 publishDir "results/mapping/bams/", mode: 'copy' input: set pair_id, file(reads) from fastq_files file index from index_files.toList() output: set pair_id, "*.bam" into bam_files file "*_report.txt" into mapping_report script: index_id = index[0] for (index_file in index) { if (index_file =~ /.*\.1\.bt2/ && !(index_file =~ /.*\.rev\.1\.bt2/)) { index_id = ( index_file =~ /(.*)\.1\.bt2/)[0][1] } } """ bowtie2 --very-sensitive -p ${task.cpus} -x ${index_id} \ -1 ${reads[0]} -2 ${reads[1]} 2> \ ${pair_id}_bowtie2_report.txt | \ samtools view -Sb - > ${pair_id}.bam if grep -q "Error" ${pair_id}_bowtie2_report.txt; then exit 1 fi """ }