Unix:merge multiple CSV files with same header by keeping the header of the first file

by 
awk 'FNR==1 && NR!=1{next;}{print}' *.csv

tested on solaris unix:

> cat file1.csv
Id,city,name ,location
1,NA,JACK,CA
>
> cat file2.csv
ID,city,name,location
2,NY,JERRY,NY
>
> nawk 'FNR==1 && NR!=1{next;}{print}' *.csv
Id,city,name ,location
1,NA,JACK,CA
2,NY,JERRY,NY
>

Explanation given by kevin-d:

FNR is the number of lines (records) read so far in the current file.
NR is the number of lines read overall. So the condition ‘FNR==1 &&
NR!=1{next;}’ says, “Skip this line if it’s the first line of the
current file, and at least 1 line has been read overall.” This has the
effect of printing the CSV header of the first file while skipping it
in the rest.

Link for the difference between awk and nawk

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