Simply run make inside.

Example: dmishura@skl:$ git clone https://github.com/carlzhc/openbsd-netcat.git Cloning into 'openbsd-netcat'... remote: Enumerating objects: 78, done. remote: Counting objects: 100% (1/1), done. remote: Total 78 (delta 0), reused 0 (delta 0), pack-reused 77 Unpacking objects: 100% (78/78), 61.52 KiB | 184.00 KiB/s, done. dmishura@skl:$ dmishura@skl:~/openbsd-netcat$ make cc -Iopenbsd-compat -Iopenbsd-lib -c netcat.c -o netcat.o netcat.c: In function ‘build_ports’: netcat.c:820:10: warning: implicit declaration of function ‘arc4random’; did you mean ‘srandom’? [-Wimplicit-function-declaration] y = (arc4random() & 0xFFFF) % (hi - lo); ^~~~~~~~~~ srandom cc -Iopenbsd-compat -Iopenbsd-lib -c atomicio.c -o atomicio.o cc -Iopenbsd-compat -Iopenbsd-lib -c socks.c -o socks.o cc -Iopenbsd-compat -Iopenbsd-lib -c openbsd-lib/arc4random.c -o openbsd-lib/arc4random.o cc -Iopenbsd-compat -Iopenbsd-lib -c openbsd-lib/readpassphrase.c -o openbsd-lib/readpassphrase.o cc -Iopenbsd-compat -Iopenbsd-lib -c openbsd-compat/base64.c -o openbsd-compat/base64.o cc -Iopenbsd-compat -Iopenbsd-lib -c openbsd-compat/bsd-str.c -o openbsd-compat/bsd-str.o openbsd-compat/bsd-str.c: In function ‘strtonum’: openbsd-compat/bsd-str.c:20:21: warning: implicit declaration of function ‘strtoll’; did you mean ‘strcoll’? [-Wimplicit-function-declaration] long long result = strtoll (nptr, &endp, 10); ^~~~~~~ strcoll cc netcat.o atomicio.o socks.o openbsd-lib/arc4random.o openbsd-lib/readpassphrase.o openbsd-compat/base64.o openbsd-compat/bsd-str.o -o nc netcat.o: In function main': netcat.c:(.text+0x62c): warning: the use of mktemp' is dangerous, better use mkstemp' or mkdtemp'

dmishura@ortce-skl:~/openbsd-netcat$ ls -la |grep nc -rwxr-xr-x 1 dmishura users 48568 Jun 8 09:31 nc -rw-r--r-- 1 dmishura users 11794 Jun 8 09:31 nc.1