cut function in linux

hi;
i have file with a lote of data
i would like to cut only numbers that start with prefix 20408

my file contain thousands of rows like this

,204080700152648,20111215,,,20
31630536259,204080662332510,20
31622520779,204080660098298,20
31651343790,204080130071280,20
31623996541,204080674586050,20
,505023501827190,20111215,204,
31620804392,204080674900896,20
31620929912,204080684300520,20
,228021302213390,20111215,204,
,204086482092214,20111215,262,
31648520081,204080679479548,20

i need only the al number start with prefix 20408

thx

---------- Post updated at 10:51 AM ---------- Previous update was at 10:49 AM ----------

i try this

cat  filenmae  |cut -d "20408" -f2 

but i received this error:

cut: the delimiter must be a single character

 nawk -F, '{for(i=1;i<=NF;i++) if ($i ~/^20408/) print $i}' myFile

The awk is probably better, but here is another way: Convert commas to newlines, remove blank lines, look for lines starting with 20408.

cat filename.txt | tr ',' '\n' | sed -e "/^$/d" | grep \^"20408"

204080700152648
204080662332510
204080660098298
204080130071280
204080674586050
204080674900896
204080684300520
204086482092214
204080679479548