c++ for unix command line operation

Question

I have a remote unix shell which I log on often to checkout files with but the system keep resetting my locals setting when I logon to it. I was planning to write the code to execute a list of commands when I log on.

#include<iostream>
#include<stdlib.h>

int main(){
 char javah[]="JAVA_HOME=/appl/usr/jdk/jdk1.6.0_20";
 char anth[]="ANT_HOME=/appl/usr/ant/instances/1.8.2";
 char path[]="PATH=$ANT_HOME/bin:$PATH";

    system("bash");
    system("cd");
    system("cd insurancePPC.11");
    system("0x0C");
    system("ls");

    putenv(javah);
    putenv(anth);
    putenv(path);
    std::cout << "JAVA_HOME=" << getenv("JAVA_HOME");
    std::cout << "\n";
    std::cout << "ANT_HOME=" << getenv("ANT_HOME");
    std::cout << "\n";
    std::cout << "PATH=" << getenv("PATH");
    std::cout << "\n";

    system("cd tools");
    std::cout << "command executed successfully...\n";
    return 0;
}

Can anyone tell me why this wasn't working as expected?

How do you plan to run this program on login? From, say, ~/.profile? Why not just put the commands in ~/.profile directly? — chepner
– chepner, Commented Aug 20, 2015 at 13:58
What does not work? Program does not output the changed environment variables? — Serge Ballesta
– Serge Ballesta, Commented Aug 20, 2015 at 13:59
Then are you planning on running this C program manually every time you log in? You can just as easily write a shell script to run manually. In fact, you'll need to do that, since your C program cannot affect your login shell's environment, only its own. The best this program can do is generate a shell script to source, but then you might as well just write that shell script in the first place. — chepner
– chepner, Commented Aug 20, 2015 at 14:01
@Sandro I have added export but it still wasn't able to work properly. — logger
– logger, Commented Aug 20, 2015 at 14:03

Community · Accepted Answer · 2017-03-20 10:18:27Z

2

cd is a built in command of the shell and only affects the current process (i.e. the current running shell.)

When you run system("cd insurancePPC.11"); it starts a new shell, that new shell changes the directory to insurancePPC.11 and exits. Your own process is unaffected by that cd command.

You are much better off writing these commands in a text file and run it as a shell script via the source command.

Create a file named myenv.sh with this content:

JAVA_HOME=/appl/usr/jdk/jdk1.6.0_20
export JAVA_HOME
ANT_HOME=/appl/usr/ant/instances/1.8.2
export ANT_HOME
PATH=$ANT_HOME/bin:$PATH
export PATH
cd
cd insurancePPC.11
ls

echo JAVA_HOME=$JAVA_HOME
echo ANT_HOME=$ANT_HOME
echo PATH=$PATH
cd tools

And from your command line run source myenv.sh Or if your shell supports it, use the shorthand . myenv.sh

edited Mar 20, 2017 at 10:18

CommunityBot

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answered Aug 20, 2015 at 14:09

nos

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Comments

chepner · Accepted Answer · 2015-08-20 14:04:35Z

2

There's no need to write a C program here. Just save the following as mysettings.sh:

export JAVA_HOME=/appl/usr/jdk/jdk1.6.0_20
export ANT_HOME=/appl/usr/ant/instances/1.8.2
PATH=$ANT_HOME/bin:$PATH
cd tools

When you log in, run

. mysettings.sh

answered Aug 20, 2015 at 14:04

chepner

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