Source code for shell commands in linux (C language)

Question

Currently, I'm implementing a simple shell in C language as my term project. I used fork and exec to execute the commands. However, some commands must be executed internally (fork and exec aren't allowed). Where can I find the source code for the shell commands?

If you're just going to copy the shell code, what is your project exactly? — Greg Hewgill
– Greg Hewgill, Commented Jun 3, 2010 at 22:08
I think he means the builtins for things like Bash ... also the closes seem unnecessary given that Dreamer could do with direction in addition to the source. — Aiden Bell
– Aiden Bell, Commented Jun 3, 2010 at 22:23

Ivan · Accepted Answer · 2010-06-03 22:10:43Z

1

Depends on which shell you want:

bash? zsh? csh?

I'd go with something smaller like the busybox shell: http://busybox.net/downloads/

answered Jun 3, 2010 at 22:10

Ivan

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R Samuel Klatchko · Accepted Answer · 2010-06-03 22:17:20Z

1

It depends on the shell command. For commands like cd, all you end up doing is calling chdir(2).

But for things like shell variables (i.e. bash's var=value), the details will greatly depend on the internals of your implementation.

answered Jun 3, 2010 at 22:17

R Samuel Klatchko

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Aiden Bell · Accepted Answer · 2010-06-03 22:20:25Z

Take a ganders at Linux Application Development by Michael K Johnson and Erik W. Troan

In my Edition (2nd) you develop a simple shell (ladsh) as part of some examples (in 10.7) in pipes and process handling. A great educational resource.

Proved very useful for me.

A snippet:

struct childProgram {
    pid_t pid;              /* 0 if exited */
    char ** argv;           /* program name and arguments */
};

struct job {
    int jobId;              /* job number */
    int numProgs;           /* total number of programs in job */
    int runningProgs;       /* number of programs running */
    char * text;            /* name of job */
    char * cmdBuf;          /* buffer various argv's point into */
    pid_t pgrp;             /* process group ID for the job */
    struct childProgram * progs; /* array of programs in job */
    struct job * next;      /* to track background commands */
};

void freeJob(struct job * cmd) {
    int i;

    for (i = 0; i < cmd->numProgs; i++) {
        free(cmd->progs[i].argv);
    }
    free(cmd->progs);
    if (cmd->text) free(cmd->text);
    free(cmd->cmdBuf);
}

You can find the full source here under ladsh1.c, ladsh2.c and so on.

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