Using awk
:
awk -v a='2,4,5,7' -v b='1,2,5,8' '
BEGIN { split(a, ax, ","); split(b, bx, ",");
for(n in ax) mapping[ bx[n] ] =ax[n];
};
NR==FNR { if (FNR in mapping) hold[ mapping[FNR] ]=$0; next; };
{ print (FNR in hold)? hold[FNR]: $0; }' fileB fileA
Here, we pass line numbers as an awk -v
ariable in a='...'
(for fileA) and b='...'
(for fileB), then we split()
them into an array on comma character as the separator (note that a
and b
were variables, while now ax
and bx
are arrays).
then we build a another mapping
array from ax
and bx
arrays to map the lines which those should be replaced in fileA with the ones from fileB;
now keys (or indexes) of the mapping
array is line numbers of the fileB and the values of these keys are the line numbers of the fileA, as below:
the mapping
array is:
Key Value
1 2
2 4
5 5
8 7
so now what we need, that is, just to read the line numbers from fileB that match with the keys above (FNRs of 1
, 2
, 5
and 8
), so we do that with:
NR==FNR { if (FNR in mapping) hold[ mapping[FNR] ]=$0; next; };
OK, now what is the value of the mapping[FNR]
? if you check the mapping
array above, that would be:
mapping[1] --> 2; then-we-have hold[ mapping[1] ] --> hold[2]=$0
mapping[2] --> 4; then-we-have hold[ mapping[2] ] --> hold[4]=$0
mapping[5] --> 5; then-we-have hold[ mapping[5] ] --> hold[5]=$0
mapping[8] --> 7; then-we-have hold[ mapping[8] ] --> hold[7]=$0
so we used the value of mapping
array as the key for the hold
array and hold
array is now contains:
Key Value
2 Argentina
4 Switzerland
5 Denmark
7 Colombia
now the last step is to use keys in hold
array as the matched line number in fileA and replace that lines with the values of that key from the hold
array if that line number found in the array or print the line itself if not found (Ternary operator: condition? if-true : if-false
), and we do that with:
{ print (FNR in hold)? hold[FNR]: $0; }
Best Answer
You can use
awk
as well:in specific case when 'linenum' file might empty, awk will skip it, so it won't print whole 'infile' lines then, to fix that, use below command:
or even better (thanks to Stéphane Chazelas):