Shell Programming and Scripting

awk -F"," -v c=${COLUMN} -v t=${USTIME} '{a[NR]=$c}END{
        asort(a);d=a[NR]-t;d=d<0?-d:d;v = a[NR]
        for(i=NR-1;i>=1;i--){
                m=a[i]-t;m=m<0?-m:m
                if(m<d){
                    d=m;v=a[i]
                }
        }
        print v
}' data.file

blah1,blah1,1453745100,blah1,blah1,blah1
blah2,blah2,1453745196,blah2,blah2,blah2
blah3,blah3,1453745296,blah3,blah3,blah3
blah4,blah4,1453745396,blah4,blah4,blah4

blah2,blah2,1453745196,blah2,blah2,blah2

awk -F"," -v c=${COLUMN} -v t=${USTIME} '{a[NR]=$c; b[NR]=$0}END{
        asort(a);d=a[NR]-t;d=d<0?-d:d;v = a[NR]; r=b[NR]
        for(i=NR-1;i>=1;i--){
                m=a[i]-t;m=m<0?-m:m
                if(m<d){
                    d=m;v=a[i]; r=b[i]
                }
        }
        print r
}' data.file

awk -F, -vc=3 -vt=1453745256 '{print ($c-t)*($c-t), $0}' file | sort -n | head -1 | cut -d" " -f2-
blah3,blah3,1453745296,blah3,blah3,blah3

awk -F, -vc=3 -vt=1453745256 '{S[$c-t)*($c-t)] = $0} END {asorti(S); print S[1]}' file

read first line and store:
          - the line itself
          - the number (or the difference between the number and the user provided value)

read the following line and
          - calculate the difference between its number and the user value
          IF this difference is smaller than the stored one
               - replace the stored line data with the current lines data
          FI
until end of file