input sample:
one
two 1578678600
awk command:
$ echo -e "one\ntwo 1578678600"|awk '{print $1,strftime("%Y-%m-%d %H:%M:%S", $2)}'
one 1970-01-01 00:00:00
two 2020-01-10 17:50:00
How strftime could ignore empty fields and not print "1970-01-01 00:00:00"? The empty field is expected to be left empty after processing.
I figured it out
$ echo -e "one\ntwo 1578678600"|awk '{if($2!="") {t=strftime("%Y-%m-%d %H:%M:%S", $2)} else {t=$2}};{print $1,t}'
one
two 2020-01-10 17:50:00
and even better:
$ echo -e "one\ntwo 1578678600"|awk '{print $1,($2 != ""? strftime("%Y-%m-%d %H:%M:%S", $2) : $2)}'
one
two 2020-01-10 17:50:00
awk 'NF==2 { $2=strftime(...) }; 1'