hsh is a simple UNIX command language interpreter that reads commands from either a file or standard input and executes them.
- Prints a prompt and waits for a command from the user
- Creates a child process in which the command is checked
- Checks for built-ins, aliases in the PATH, and local executable programs
- The child process is replaced by the command, which accepts arguments
- When the command is done, the program returns to the parent process and prints the prompt
- The program is ready to receive a new command
- To exit: press Ctrl-D or enter "exit" (with or without a status)
- Works also in non interactive mode
gcc -Wall -Werror -Wextra -pedantic -std=gnu89 *.c -o hsh
Usage: hsh [filename]
To invoke hsh, compile all .c files in the repository and run the resulting executable.
hsh can be invoked both interactively and non-interactively. If hsh is invoked with standard input not connected to a terminal, it reads and executes received commands in order.
Example:
$ echo "echo 'hello'" | ./hsh 'hello' $
If hsh is invoked with standard input connected to a terminal (determined by isatty(3)), an interactive shell is opened. When executing interactively, hsh displays the prompt $ when it is ready to read a command.
Example:
Alternatively, if command line arguments are supplied upon invocation, hsh treats the first argument as a file from which to read commands. The supplied file should contain one command per line. hsh runs each of the commands contained in the file in order before exiting.
Example:
$ cat test echo 'hello' $ ./hsh test 'hello' $
Upon invocation, hsh receives and copies the environment of the parent process in which it was executed. This environment is an array of name-value strings describing variables in the format NAME=VALUE. A few key environmental variables are:
The home directory of the current user and the default directory argument for the cd builtin command.
$ echo "echo $HOME" | ./hsh /home/projects
The current working directory as set by the cd command.
$ echo "echo $PWD" | ./hsh /home/projects/alx/simple_shell
The previous working directory as set by the cd command.
A colon-separated list of directories in which the shell looks for commands. A null directory name in the path (represented by any of two adjacent colons, an initial colon, or a trailing colon) indicates the current directory.
After receiving a command, hsh tokenizes it into words using " " as a delimiter. The first word is considered the command and all remaining words are considered arguments to that command. hsh then proceeds with the following actions:
1.If the first character of the command is neither a slash () nor dot (.), the shell searches for it in the list of shell builtins. If there exists a builtin by that name, the builtin is invoked. 2.If the first character of the command is none of a slash (), dot (.), nor builtin, hsh searches each element of the PATH environmental variable for a directory containing an executable file by that name. 3.If the first character of the command is a slash () or dot (.) or either of the above searches was successful, the shell executes the named program with any remaining given arguments in a separate execution environment.
hsh returns the exit status of the last command executed, with zero indicating success and non-zero indicating failure.
If a command is not found, the return status is 127; if a command is found but is not executable, the return status is 126.
All builtins return zero on success and one or two on incorrect usage (indicated by a corresponding error message).
While running in interactive mode, hsh ignores the keyboard input Ctrl+c. Alternatively, an input of end-of-file (Ctrl+d) will exit the program.
User hits Ctrl+d in the third line. $ ./hsh $ ^C $ ^C $
hsh interprets the $ character for variable replacement.
ENV_VARIABLE is substituted with its value.
Example: $ echo "echo $PWD" | ./hsh /home/projects/alx/simple_shell
? is substitued with the return value of the last program executed.
Example: $ echo "echo $?" | ./hsh 0
##$$
The second $ is substitued with the current process ID.
Example:
$ echo "echo $$" | ./hsh 6494
hsh ignores all words and characters preceeded by a # character on a line.
Example: $ echo "echo 'hello' #this will be ignored!" | ./hsh 'hello'
##Operators
hsh specially interprets the following operator characters:
; - Command separator Commands separated by a ; are executed sequentially.
Example:
$ echo "echo 'hello' ; echo 'world'" | ./hsh 'hello' 'world'
command1 && command2: command2 is executed if, and only if, command1 returns an exit status of zero.
Example:
$ echo "error! && echo 'hello'" | ./hsh ./hsh: 1: error!: not found $ echo "echo 'all good' && echo 'hello'" | ./hsh 'all good' 'hello'
command1 || command2: command2 is executed if, and only if, command1 returns a non-zero exit status.
Example:
$ echo "error! || echo 'but still runs'" | ./hsh ./hsh: 1: error!: not found 'but still runs'
The operators && and || have equal precedence, followed by ;.
- Usage: cd [DIRECTORY] Changes the current directory of the process to DIRECTORY.
- If no argument is given, the command is interpreted as cd $HOME.
- If the argument - is given, the command is interpreted as cd $OLDPWD and the pathname of the new working directory is printed to standad output.
- If the argument, -- is given, the command is interpreted as cd $OLDPWD but the pathname of the new working directory is not printed.
- The environment variables PWD and OLDPWD are updated after a change of directory. Example:
$ ./hsh $ pwd /home/projects/alx/simple_shell $ cd ../ $ pw /home/projects/alx $ cd - $ pwd /home/projects/alx/simple_shell
- Usage: alias [NAME[='VALUE'] ...]
- Handles aliases.
- alias: Prints a list of all aliases, one per line, in the form NAME='VALUE'.
- alias NAME [NAME2 ...]: Prints the aliases NAME, NAME2, etc. one per line, in the form NAME='VALUE'.
- alias NAME='VALUE' [...]: Defines an alias for each NAME whose VALUE is given. If name is already an alias, its value is replaced with VALUE. Example:
$ ./hsh $ alias show=ls $ show AUTHORS builtins_help_2.c errors.c linkedlist.c shell.h test README.md env_builtins.c getline.c locate.c hsh alias_builtins.c environ.c helper.c main.c split.c builtin.c err_msgs1.c helpers_2.c man_1_simple_shell str_funcs1.c builtins_help_1.c err_msgs2.c input_helpers.c proc_file_comm.c str_funcs2.c
- Usage: exit [STATUS]
- Exits the shell.
- The STATUS argument is the integer used to exit the shell.
- If no argument is given, the command is interpreted as exit 0. Example:
$ ./hsh $ exit
- Usage: env
- Prints the current environment. Example:
$ ./hsh $ env NVM_DIR=/home/projects/.nvm ...
- Usage: setenv [VARIABLE] [VALUE]
- Initializes a new environment variable, or modifies an existing one.
- Upon failure, prints a message to stderr. Example:
$ ./hsh $ setenv NAME Poppy $ echo $NAME Poppy
- Usage: unsetenv [VARIABLE]
- Removes an environmental variable.
- Upon failure, prints a message to stderr. Example:
$ ./hsh $ setenv NAME Poppy $ unsetenv NAME $ echo $NAME
$
1: MOHAMMED USMAN 2: ABDUROHMAN AHMED