Related to question 3451993, is it possible to call a function which is internal to subst.c (in the Bash source code) in a Bash script?
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6 Answers
Bash supports loadable builtins. You might be able to make use of this to do what you want. See the files in your /usr/share/doc/bash/examples/loadables (or similar) directory.
answered Aug 10, 2010 at 22:58
Dennis Williamson
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2 Comments
l0b0
Good idea. Unfortunately
grep subst /usr/share/doc/bash/examples/loadables/* returned nothing.
Dennis Williamson
@l0b0: That just means you have to write your own. Also,
grep subst /usr/include/bash/* gives /usr/include/bash/shell.h:#include "subst.h", grep shell.h /usr/share/doc/bash/examples/loadables/* gives a bunch. Unfortunately, grep prompt /usr/share/doc/bash/examples/loadables/* gives nothing, but grep prompt /usr/include/bash/subst.h does look interesting.It even possible to use C data structures ;)
This is ctypes.sh, a foreign function interface for bash. ctypes.sh is a bash plugin that provides a foreign function interface directly in your shell. In other words, it allows you to call routines in shared libraries from within bash.
Check out https://github.com/taviso/ctypes.sh ;)
1 Comment
mljrg
This is the most interesting project I have seen in the past couple of years. Thanks for you answer!
The simplest way to do this is to write a simple program that collects the input, feeds it to the function, then prints the result. Why don't you tell us what you are attempting to accomplish and perhaps we can suggest an easier way to "skin this cat".
5 Comments
l0b0
I'm trying to call a function which is internal to Bash, but it looks like it's not compiled into a separate shell command. Please see the link for more info.
Jay
It's very difficult to do this and is usually very unreliable. You're better off trying to get what you want a different way.
msw
@l0b0: restating the question is not equivalent to saying what you are trying to accomplish.
user2284570
The simplest way to do this is to write a simple program that collects the input, feeds it to the function, then prints the resultHow do you do this on chrome os? It is the case where all partitions are mounted with noexec except for the rootfs which is write protected.Jay
Never used Chrome OS. It sounds like they don't allow you to execute anything. If that's true you won't have a simple hack. You'd probably have to write a plugin for chrome.
No.
You can't access a function internal to the shell binary from the shell if it is not exported as a shell function.
1 Comment
Chris
"If it is not exported as a shell function" -- can you explain more about that option? I am asking for two reasons: 1) powershell provides this ability natively, eg
[System.DateTime]::Now; 2) I am looking for a Linux/BASH analog that does not involve me writing more than the merest whisper of C code (I'll need an SOW or I'll be doing it in my free time). To complement this, I have reviewed guile and I am familiar with python's cffi library in addition to the python compiler nuitka. I can also use go...so any BASH/C version of this will need to be pretty easy or well-motivatedThis code looks pretty elegant: (from here) Its the same solution @Jay pointed out.
bash$ cat testing.c
#include <stdio.h>
char* say_hello()
{
return "hello world";
}
float calc_xyzzy()
{
return 6.234;
}
int main(int argc, char** argv)
{
if (argc>1) {
if (argv[1][0] =='1') {
fprintf(stdout,"%s\n",say_hello());
} else if ( argv[1][0] == '2') {
fprintf(stdout,"%g\n",calc_xyzzy());
}
}
return 0;
}
bash$ gcc -o testing testing.c
bash$ ./testing 1
hello world
bash$ ./testing 2
6.234
bash$ var_1="$(./testing 1)"
bash$ var_2="$(./testing 2)"
bash$ echo $var_1
hello world
bash$ echo $var_2
6.234
bash$
Comments
No, you'll have to write a short C program, compile it and call it from the shell.
