OS system calls from bash script

Question

Is it possible to call os system calls like open, close etc from a shell script? I tried googling but it takes me in the wrong direction of using "system()" command. Can some one help on this?

Answer 1

Many syscalls are accessible, but only via the native shell mechanisms, rather than being able to directly specify exact parameters. For instance:

exec 4>outfile

calls:

open("outfile", O_WRONLY|O_CREAT|O_APPEND, 0666) = 3
dup2(3, 4)

(with 3 being replaced by the next available descriptor), and

exec 4<&-

calls:

close(4)

Some shells, such as bash, allow additional builtins to be added through loadable modules (see the enable builtin, used to load such modules); if you really needed functionality not provided upstream, you could potentially implement it that way.