▪️Functions

We can use some function that we already know (like printf, malloc, free, etc) so I will not describe them here.

You will probably not use all of these functions but at least you have somewhere where you can easily find links to the manual pages. And for some, an example on how to use them.

readline()

char *readline (const char *prompt);

The readline() function reads a line from the terminal and returns it, using prompt as a prompt. If no prompt is given as parameter, no prompt will be shown in the terminal. The line returned is allocated with malloc and we have to free it ourselves.

readline()

#include <stdio.h>
#include <readline/readline.h>
#include <readline/history.h>

int main(void)
{
    char *rl;
    rl = readline("Prompt > ");
    printf("%s\n", rl);
    return (0);
}

Compiling this programm and running will result in the following.

$> ./minishell
Prompt > Hi ! How are you ?
Hi ! How are you ?
$>

You can find more information about readline() here.

rl_clear_history()

void rl_clear_history(void);

The rl_clear_line() function clears the history list by deleting all of the entries. The rl_clear_line() function frees data that the readline library saves in the histroy list.

rl_on_new_line()

int rl_on_new_line(void);

The rl_on_new_line() function tells the update routine that we have moved onto a new empty line, usually used after outputting a line.

rl_replace_line()

I didn't find any information on that function.

rl_redisplay()

int rl_redisplay(void);

The rl_redisplay() change what's displayed on the screen to reflect the current contents of rl_line_buffer.

add_history()

void add_history(char *s);

The add_history() function saves the line passed as parameter in the history so it can be retrieved later in the terminal (like pressing the up arrow in bash).

getcwd()

#include <unistd.h>
char *getcwd(char *buf, size_t size);

The getcwd() returns a null-terminated string containing the absolute pathname that is the current working directory of the calling process. The pathname is returned as the function result and via the argument buf.

getcwd() example

#include <unistd.h>
#include <stdio.h> // for printf

int main(void)
{
    char *pwd;
    
    pwd = getcwd(NULL, 0);
    printf("pwd: %s\n", pwd);
    return (0);
}

$> pwd: /Users/saeby/Documents/tmp

You can find more information about getcwd() here.

chdir()

#include <unistd.h>
int chdir(const char *path);

chdir() changes the current working directory of the calling process to the directory specified in path.

chdir() example

#include <unistd.h>
#include <stdio.h> // for printf

int main(void)
{
    char *pwd;
    
    pwd = getcwd(NULL, 0);
    printf("pwd before chdir: %s\n", pwd);
    chdir("/Users/saeby/Documents/42/minishell");
    pwd = getcwd(NULL, 0);
    printf("pwd after chdir: %s\n", pwd);
    return (0);
}

$> pwd before chdir: /Users/saeby/Documents/tmp
$> pwd after chdir: /Users/saeby/Documents/42/minishell

You can find more information about chdir() here.

stat() & lstat() & fstat()

#include <sys/stat.h>
int stat(const char *restrict pathname, struct stat *restrict statbuf);
int lstat(const char *restrict pathname, struct stat *restrict statbuf);
int fstat(int fd, struct stat *statbuf);

These functions return information about a file in the structure pointed to by statbuf.

You can find more detailed information about these functions here.

opendir()

#include <sys/types.h>
#include <dirent.h>
DIR *opendir(const char *name);

The opendir() function opens a directory stream corresponding to the directory name, and returns a pointer to the directory stream. The stream is positioned at the first entry in the directory.

You can find more information about the opendir function here.

readdir()

#include <dirent.h>
struct dirent *readdir(DIR *dirp);

The readdir() function returns a pointer to a dirent structure representing the next directory entry in the directory stream pointed to by dirp. It returns NULL on reaching the end of the directory stream or if an error occured.

You can find more information about readdir here.

closedir()

#include <sys/types.h>
#include <dirent.h>
int closedir(DIR *dirp);

The closedir() function closes the directory stream associated with dirp. A successful call to closedir() also closes the underlying file descriptor associated with dirp. The directory stream descriptor dirp is not available after this call.

You can find more information about closedir here.

strerror()

#include <string.h>
char *strerror(int errnum);

The strerror() function returns a pointer to a string that describes the error code passed in the argument errnum. This string must not be modified by the application, but may be modified by a subsequent call to strerror() or strerror_l(). No other library function, including perror(), will modify this string.

You can find more information about strerror here.

perror()

#include <stdio.h>
void perror(const char *s);

The perror() function produces a message on standard error describing the last error encountered during a call to a system or library function.

You can find more information about perror here.

isatty()

#include <unistd.h>
int isatty(int fd);

The isatty function tests wether fd is a terminal.

You can find more information about isatty here.

ttyname()

#include <unistd.h>
char **ttyname(int fd);

The ttyname() function returns a pointer to the null-terminated pathname of the terminal device that is open on the file descriptor fd, or NULL on error.

You can find more information about ttyname() here.

ttyslot()

#include <unistd.h>
int ttyslot(void);

This is a legacy function with some backstory, you can read all about it and how it works here.

ioctl()

#include <sys/ioctl.h>
int ioctl(int fd, unsigned long request, ...);

The ioctl() system call manipulates the underlying device parameters of a special files. You can find more detailed information here.

getenv()

#include <stdlib.h>
char *getenv(const char *name);

The getenv() function searches the environment list to find the environment variable name, and returns a pointer to the corresponding value string.

You can find more information about getenv() here.

tcsetattr()

#include <termios.h>
int tcsetattr(int fildes, int optional_actions, const struct *termios_p);

The tcsetattr() function shall set the parameters associated with the terminal referred to by the open file descriptor fildes from the termios structure referenced by termios_p as described here.

tcgetattr()

#include <termios.h>
int tcgetattr(int fildes, struct termios *termios_p);

The tcgetattr() function shall get the parameters associated with with the terminal reffered to by fildes and store them in the termios structure referenced by termios_p.

You can find more detailed information here.

tgetent()

#include <curses.h>
#include <term.h>
int tgetent(char *bp, const char *name);
int tgetflag(char *id);
int tgetnum(char *id);
char *tgetstr(char *id, char **area);
char *tgoto(const char *cap, int col, int row);
int tputs(const char *str, int affcnt, int (*putc)(int));

These routines are included as a conversion aid for programs that use the termcap library. You can find more information about all of them here.