simple way to get reads length distribution of FASTQ files

• Using perl: 

cat input.fq | perl -ne '$s=<>;<>;<>;chomp($s);print length($s)."\n";' > input.readslength.txt

• Using awk:

cat input.fq | awk '{if(NR%4==2) print length($1)}' > input.readslength.txt

• if zipped file, using:

 zcat input.fq.gz | ...

• get length statistics:

sort input.readslength.txt | uniq -c

• or using fancy code from Jim Kent's utility:

textHistogram


So, one line code for all input fastq files would be:

find *.fq.gz -not -name \*raw\* -printf "zcat %p | awk '{if(NR%%4==2) print length(\$1)}' | textHistogram -maxBinCount=59 stdin \n" | sh


Note that you have to use double % to escape the % character for printf formatting control, just like in C. (Thanks for zencuke's answer here)

You will get something like this:

RNAseq.20E_library.result_primary.clean.fa

large values truncated: need 35 bins or larger binSize than 1

Maximum value 53.000000

 18 ********* 27730

 19 ******************* 58997

 20 ************************************************************ 186919

 21 ************************ 74536

 22 ************** 45171

 23 ************* 39107

 24 *************** 45560

 25 *********************** 70452

 26 ************************************************* 154030

 27 ************************************************************ 187704

 28 ************************** 81198

 29 ***** 17016

 30 ** 5341

 31 * 2439

 32  0

 33  1

 34  0

 35  0

 36  0

 37  0

 38  0

 39  1

<minVal or >= 40  173

RNAseq.Day_13_library.result_primary.clean.fa

large values truncated: need 35 bins or larger binSize than 1

Maximum value 53.000000

 18 ***** 22570

 19 ********* 40335

 20 ***************************** 127999

 21 ********************* 95179

 22 ****************** 79808

 23 ********* 39596

 24 ******* 29423

 25 ************* 55438

 26 ************************************* 164868

 27 ************************************************************ 265722

 28 *************************** 120353

 29 ********* 38625

 30 *** 14684

 31 * 5214

 32  0

 33  0

 34  1

<minVal or >= 35  140