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 the system() command. Can some one help on this?

Headwards

Why not just use the normal mechanisms for dealing with files? – Marlie

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.

Nutbrown

Answer 2

It depends on the system. For example AIX has a syscall command for this

syscall [ -n ] Name [ Argument1 ... ArgumentN ] [  ; Name [ Argument1 ... ArgumentN ] ] ...

Plan9 also has a similar command:

syscall [ -o ] entry [ arg ...  ]

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On Linux there's no such command but there's mauri870/syscall which is

... an effort to port the plan9 syscall command to Linux.

For example

$ ./syscall write 1 Hello$'\n'World$'\n' 12
Hello
World
$ ./syscall -o read 0 buf 5
xyz
xyz
$ ./syscall -ov getcwd buf 100
Syscall return: 23
/home/user/src/syscall

---

Another port is oliwer/syscall

syscall [-<n>] name [args...] [, name [args...]]...

Example usage:

syscall open /my/file 1 0755 , write \$0 hello \#hello , close \$0
syscall open /dev/random 0 , echo \$0

Swanson