perl fasta_to_fastq.pl reads.fasta > my_converted_fasta.fq

Using BBMap:

cat *.fasta | reformat.sh in=stdin.fa out=x.fq

There are few situations where this would be useful.

Assuming that script is valid you can probably just do a loop over the input files, e.g.:

for f in *.fasta ; do perl fasta_to_fastq.pl $f > $f.conv.fq ; done