Shell Programming and Scripting

$ cat printzero.c

#include <stdio.h>

int main(int argc, char *argv[])
{
        printf("$0 is %s\n", argv[0]);
}

$ cat zero.c

#include <unistd.h>
#include <stdio.h>

int main(int argc, char *argv[])
{
        if(argc < 2)
        {
                fprintf(stderr, "usage:  ./zero program zeroth-argument\n");
                return(1);
        }

        // First argument is the program name and path.  Second is $0.
        // Note that NOTHING forces them to be the same.
        execl(argv[1], argv[2], NULL);
        return(1);
}

$ gcc zero.c -o zero
$ gcc printzero.c -o printzero
$ ./printzero

$0 is ./printzero

$ ./zero ./printzero slartibartfast

$0 is slartibartfast

$

checking the current dir
go to other dir
execute something there
come back to previous directory

#!/bin/bash

die() {
        echo -- "$@" >&2
        exit 1
}

. /etc/profile

[ -z "$MYDIRVAR" ] && die "MYDIRVAR not set in /etc/profile"
[ -e "$MYDIRVAR" ] || die "MYDIRVAR=$MYDIRVAR does not exist"
[ -d "$MYDIRVAR" ] || die "MYDIRVAR=$MYDIRVAR is not a directory"
[ -f "$MYDIRVAR"/myscript.sh ] || die "MYDIRVAR=$MYDIRVAR does not contain myscript.sh"

echo "MYDIRVAR=$MYDIRVAR, folder exists and contains myscript.sh, ready to go" >&2