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Minishell

name	library	description	return	required for
readline	readline.h	reads a line from the terminal and returns it	NULL if EOF, empty for empty line, returns text of line as char*, needs to be free'd	reading input from the terminal, allowing it to be edited before processed by shell
rl_clear_history	readline.h	Clears the history list of previous input	void	Useful for resetting the history list between commands or sessions
rl_on_new_line	readline.h	reset prompt
rl_replace_line	readline.h	Replaces the current input line with a new one. if empty str: command line buffer is cleared
rl_redisplay	readline.h	display prompt again
add_history	readline.h	Adds a line of text to the history list	void	Useful for adding previously entered commands to the history list
printf	stdio.h	Outputs text to the console	int (the number of characters printed)
malloc	stdlib.h	Allocates a block of memory on the heap (size specified)	void * (a pointer to the allocated memory)
free	stdlib.h	Deallocates a previously allocated block of memory	void
write	unistd.h	Writes data to a file descriptor	ssize_t (the number of bytes written)	Useful for outputting text and data to files and other output destinations
access	unistd.h	Tests whether a file exists and can be accessed
open	fcntl.h	Opens a file and returns a file descriptor	int (fd of the opened file)	Used for opening files for reading or writing
read	unistd.h	Reads data from a file descriptor	ssize_t (the number of bytes read)	Used for reading data from files or other input sources
close	unistd.h	Closes a file descriptor	int (0 if successful, otherwise -1 )	Used for closing file descriptors (when no longer needed)
fork	unistd.h	Creates a related new process (child) by duplicating the calling one (parent)	pid_t In the parent process: the process ID of the child process, while in the child process it returns 0. -1 if error occured.	Used for creating new processes to run shell commands in (otherwise the parent process would be replaced and terminated - ending the program)
wait	sys/wait.h	Waits for a child process to terminate	pid_t (the process ID of the terminated child) or -1 if no children are there to wait for	Used for synchronizing the execution of multiple processes in a shell
waitpid	sys/wait.h	Waits for a specific child process to terminate	pid_t (the process ID of the terminated child)	Used for synchronizing the execution of specific child processes in a shell
wait3	sys/wait.h
wait4	sys/wait.h
signal	signal.h	Sets a signal handler function for a specific signal. Sigaction is better but needs a new struct	sighandler_t (the previous signal handler function)	Used for handling signals, such as interrupts or errors
sigaction	signal.h	Sets a signal handler function with additional options for a specific signal	struct sigaction* (the previous signal action)	Similar to signal(), but provides more options for handling signals
sigemptyset	signal.h	Initializes a signal set to be empty	int (0 if successful, -1 otherwise)
sigaddset	signal.h
kill	signal.h	Sends a signal to a process or group of processes	int (0 if successful, -1 otherwise)	Used for sending a signal to a process, such as terminating it or requesting it to perform a specified action (by sighandler func)
exit	stdlib.h	Terminates the current process	void	Useful for terminating the shell or a child process when it has finished executing
getcwd	unistd.h	Gets the current working directory of the process	char* (a pointer to a string containing the directory path)
chdir	unistd.h	Changes the current working directory of the process	int (0 if successful, -1 otherwise)	Used for changing the current working directory, which affects the location of file paths used in the shell
stat	sys/stat.h	Gets information about a file	int (0 if successful, -1 otherwise)	Used for getting information: size, permissions, and modification time
lstat	sys/stat.h	Gets information about a file, but does not follow symbolic links	int (0 if successful, -1 otherwise)	Similar to stat(), but does not follow symbolic links when getting information about a file
fstat	sys/stat.h	Gets information about a file from a file descriptor	int (0 if successful, -1 otherwise)	Similar to stat(), but gets information about a file from a file descriptor instead of a file path
unlink	unistd.h	Deletes a file or symbolic link	int (0 if successful, -1 otherwise)	Used for deleting a file or symbolic link from the file system
execve	unistd.h	Replaces the current process with a new one. Old process terminates!!!	int (0 if successful, -1 otherwise)	Used for running shell commands by replacing the current process with the one that executes the command
dup	unistd.h	Duplicates a file descriptor	int (a new file descriptor that refers to the same file
dup2	unistd.h
pipe	unistd.h
opendir
readdir
closedir
strerror	string.h	Gets a string describing an error code	char* (a pointer to a string describing the error code)
perror	stdio.h	Prints an error message to stderr with a prefix	void
isatty	unistd.h	Checks whether a file descriptor refers to a terminal
ttyname	unistd.h	Gets the name of the terminal device associated with a file descriptor	char* (a pointer to a string containing the name of the terminal)
ttyslot
ioctl
getenv	stdlib.h	gets an environment variable specified as argument	if found, returns value string, NULL if there is no match	used to find the full path to functions
tcsetattr	termios.h	Sets the terminal attributes for a file descriptor	int (0 if successful, -1 otherwise)
tcgetattr	termios.h	Gets the terminal attributes for a file descriptor	int (0 if successful, -1 otherwise)
tgetent
tgetflag
tgetnum
tgetstr
tgoto
tputs

Useful links

• Bash manual

• Building a simple shell: tutorial explaining how to build a very simple shell from the ground up

• Minishell project of other 42 students

• Tutorial - write a shell in C

• Tutorial- Step by step instruction how to recreate shell

• History of bash: explains quite well how it is structured, but doesn't show code examples