LinuxQuestions.org - How to read content environment file?

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How to read content from environment file?

Hi, guys.
I plan to read some words from environment files, such as

$(HOME)/.bash

How can I open such files and fetch lines? Thanks a lot!

In what programming language?

o, is it related to language and shell?

It's C language on linux shell. And the complete path is
$(HOME)/.adcl/config.adcl

Thanks!

How long have you been doing GNU/Linux & how long have you been doing C?

I don't mean that to sound rude, but ...

There is no "linux shell" per se, only a default linux shell, which is bash. Is this the shell you are referring to?

Also, opening files & reading them is almost the next lesson after "Hello World" in learning a programming language; if you need to do this in C, I suggest a text book. (And, unfortunately, I don't do C, so I can't make any recommendations.)

Finally, are you sure "$(HOME)" is correct syntax? In bash that would be "${HOME}", or "$HOME", or just "~".

archtoad6:

Thanks for reply.

I wrote shell scripts before, seldom people call that bash scripts. So when you ask what shell, I also doubt us there any else shell?:)

Sure, I know how to open/read/write user-defined files in C. However, I don't know how to access environment variables such as $HOME and .adcl in c programming. That's why I post my questin here.

More specified, my question is how to open $HOME/.adcl/config.adcl in C?

Quote:

Originally Posted by ArthurHuang

I don't know how to access environment variables such as $HOME and .adcl in c programming.

".adcl" is just a normal directory name. The fact that it starts with a dot, just makes the command like "ls" not show it by default. Nothing more..

Quote:

Originally Posted by ArthurHuang

More specified, my question is how to open $HOME/.adcl/config.adcl in C?

Here's a complete example:

Code:

/* example.c - How to use an environment variable in C */



#include <stdio.h>

#include <stdlib.h>

#include <string.h>

#include <errno.h>

#include <limits.h>



int main(int argc, char *argv[])

{

    char c;

    int result;

    char *homedir;

    char filepath[PATH_MAX];

    FILE* fp;



    homedir = getenv("HOME");

    if (homedir == NULL) {

          fprintf(stderr, "Environment variable HOME not found\n");

          exit(1);

    }

    result = snprintf(filepath, PATH_MAX, "%s/.adcl/config.adcl", homedir);

    if (result >= PATH_MAX) {

          fprintf(stderr, "Warning: path \"%s\" too long. Truncated.\n", filepath);

    }



    fp = fopen(filepath, "r");

    if (fp == NULL) {

          fprintf(stderr, "Could not open %s. %s\n", filepath, strerror(errno));

          exit(1);

    }

    printf("Outputting contents of %s:\n\n", filepath);

    while ((c = fgetc(fp)) != EOF) {

          fputc(c, stdout);

    }

    fclose(fp);

    return 0;

}

Compile with:

Code:

gcc -Wall -o example example.c

Ah, a C person answered while I was composing this. I think you need to use Google to learn about the variety shells available in GNU/Linux.

You also should have used it to get the answer to your underlying question before posting here.

Remember, I already said I don't write C, but I still found your basic answer w/ 1 search Google Linux:

C "access envirronment variables"

Thank you HKO very much.
I don't expect to have the complete or exactly answer here, but you know, any suggestion or advice is a good advice to go ahead in a correct direction. And we can also learn more from others' posts. I thinks that's the reason why many people post questions here.