Hi all,

I'm trying to write some code to generate mean read length data from a range of fastq files. 
awk '{if(NR%4==2) print NR"\t"$0"\t"length($0)}' HG1.fastq > readLength.txt 

i've got as far as here from looking through other posts and trying to improve but i'm stuck on a couple of things. This command only works on a single file and will report the length of each read within that file separately.

I want to run a single command so the mean and Standard Dev of read lengths from all .fastq files within a folder are reported in a single .txt file, one sample per line. I gues SD might be difficult to calculate in a command so even just the mean read length.

e.g.the first 5 files in my folder are:
ru1.fastq
ru2.fastq
hg3.fastq
hg25.fastq
ru7.fastq

obviously i'm a bit of a novice at this so all help would be appreciated !!

thanks a lot
Using awk:

    awk 'BEGIN { t=0.0;sq=0.0; n=0;} ;NR%4==2 {n++;L=length($0);t+=L;sq+=L*L;}END{m=t/n;printf("total %d avg=%f stddev=%f\n",n,m,sq/n-m*m);}'  *.fastq