ksh93 libshell

In a number of posts about a year ago I discussed how to develop custom builtins for Korn Shell 93 (ksh93) using libshell and published APIs. You can also use these same APIs to access ksh93 functionality from within a C application. This post provides three simple examples of how to do this.

The first example simply takes two numbers as arguments on the command line, multiplies the numbers and prints out the result on stderr.

#include <shell.h>
#include <nval.h>

int main(int argc, char *argv[])
{
    Namval_t *np;
    Sfdouble_t res;

    Shell_t *shp = sh_init(argc, argv, 0);
    sh_trap("((xresult=$0*$1))", 0);

    np = nv_open("xresult", shp->var_tree, 0);
    res = nv_getnum(np);
    sfprintf(sfstderr,"%Lg\n", res);
    nv_close(np);

    return(0);
}

Here is how to compile this example using static libraries. I built these examples in my home directory but the ksh93 build environment is at /work/ksh93, hence the use of -I and -L options. Note the large number of AST (Advanced Software Toolkit) and ksh93 libraries you have to specify in order to resolve all the symbols.

gcc -o example1 -I/work/ksh93/arch/linux.i386-64/include/ast example1.c -L/work/ksh93/arch/linux.i386-64/lib -lshell -lm -ldll -lcmd  -ldl -last 

For example:

$ ./example1 3 4 
12
$ 

The next example breaks the text string string into its component parts and prints them out to stdout. Note that "foo\\ bar" is one word, not two words.

#include <shell.h>
#include <stdio.h>
#include <nval.h>

int
main(int argc, char *argv[])
{
    char tmp[512];
    char string[] ="hello world 'my name is Finnbarr' foo\\ bar";

    sprintf(tmp, "set - %s && for i in \"$@\";\n do\n echo \"$i\"\ndone", string);

    Shell_t *shp = sh_init(argc, argv, 0);
    sh_trap(tmp, 0);

    return(0);
}

Here is the output:

./example2
hello
world
my name is Finnbarr
foo bar

The next example is similar to the previous example, except that it creates an array and then uses nv_getval() to access the contents of the created array and print the contents to stderr.

#include <shell.h>
#include <stdio.h>
#include <nval.h>

int 
shell(int argc, char* argv[], char *str)
{
    Namval_t *np, *np_sub;
    char tmp[512];

    sprintf(tmp, "set - %s && for i in \"$@\";\n do\n aname+=(\"$i\")\ndone", str);

    Shell_t *shp = sh_init(argc, argv, 0);
    sh_trap(tmp, 0);

    np = nv_open("aname", shp->var_tree, 0);
    nv_putsub(np, NULL, ARRAY_SCAN);
    np_sub = np;

    do {
        // copy out the arguments to wherever here. 
        fprintf(stderr, "%d: subscript='%s' value='%s'\n", np_sub, nv_getsub(np_sub), nv_getval(np_sub));
    } while (np_sub && nv_nextsub(np_sub)); 

    nv_close(np);

    return(0);
} 

int 
main(int argc, char *argv[])
{
    char string[] ="hello world 'my name is simon' foo\\ bar";

    shell(argc, argv, string);
}

Here is the output:

$ ./example1
37212336: subscript='0' value='hello'
37212336: subscript='1' value='world'
37212336: subscript='2' value='my name is simon'
37212336: subscript='3' value='foo bar'
$ 

As you can see, running shell script snippets from within a C application is not difficult. For more information on these APIs read the ksh93 shell(3) and nval(3) man pages.