This folder/directory displays all the under-pinnings of a Simple Shell in C programming language

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In this task, a Manual Page (man page using the groff format) for the simple shell, as well as a Readme file explaining the entire project should be made available. Also a file that lists all the names of the authors is very much required for the completion of this task.

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In this task, all file must pass through all the checks of the Betty Linter. The task is considered completed when all files meets the Betty requirements.

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A shell script is written to display prompt and execute one-word command lines (commands without arguments and options). The shell script also handles error.

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A shell script is written to display prompt and execute command lines with arguments and options. The shell script also handles error.

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An updated shell script from task 3 to handle the PATH, and dosen't call fork if the file dosen't exist.

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An updated shell script from task 4 that implements the exit and dosen't handle any exit built-in arguments.

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An updated shell script from task 5 that implements the ENV built-in which prints the current environment

/****** Task 7 *******/

In this task, a blog post describing step by step what happens when you type ls -l *.c and hit Enter in a shell must be written and publlished. It should also be posted on LinkedIn and other social media platforms.

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A group class work that should be tested in a single respository with every team contributing to the repository.

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An updated shell script from task 6 that impliments the getline function.

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An updated shell script from task 9 that does not use strtok.

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An updated shell script from task 10 that handles arguments for the built-in exit. Usage: exit status, where status is an integer used to exit the shell.

/****** Task 12 *******/

An updated shell script from task 11 that handles Ctrl+C, the shell should not quit when the user inputs ^C.

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An updated shell script from task 12 that 1mplement the setenv and unsetenv builtin commands.

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An updated shell script from task 13 that implement the builtin command cd which changes the current directory of the process. Command syntax: cd [DIRECTORY]. If no argument is given to cd the command must be interpreted like cd $HOME.It also has to handle the command cd -. You have to update the environment variable PWD when you change directory.

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An updated shell script from task 14 that handles the commands separator.

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An updated shell script from task 15 handles the && and || shell logical operators.

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An updated shell script from task 16 that implements the alias builtin command.

Usage: alias [name[='value'] ...] alias: Prints a list of all aliases, one per line, in the form name='value' alias name [name2 ...]: Prints the aliases name, name2, etc 1 per line, in the form name='value'. alias name='value' [...]: Defines an alias for each namewhosevalueis given. Ifnameis already an alias, replaces its value withvalue`.

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An updated shell script from task 17 that handles variables replacement, and also handles the $? variable and the $$ variable.

/****** Task 19 *******/

An updated shell script from task 18 that handles comments (#).

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An updated shell script from task 19 that implements the help built-in. Usage: help [BUILTIN].

/****** Task 21 *******/

An updated shell script from task 20 that implements the history built-in, without any argument. The history built-in displays the history list, one command by line, preceded with line numbers (starting at 0) On exit, write the entire history, without line numbers, to a file named .simple_shell_history in the directory $HOME. When the shell starts, read the file .simple_shell_history in the directory $HOME if it exists, and set the first line number to the total number of lines in the file modulo 4096.

/****** Task 22 *******/

An updated shell script from task 21 that implements files input. Usage: simple_shell [filename] Your shell can take a file as a command line argument The file contains all the commands that your shell should run before exiting The file should contain one command per line In this mode, the shell should not print a prompt and should not read from stdin.

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Description 💬

​ hsh is a simple UNIX command language interpreter that reads commands from either a file or standard input and executes them. ​

Invocation 🏃

​ Usage: hsh [filename] ​ To invoke shellby, compile all .c files in the repository and run the resulting executable: ​

gcc *.c -o hsh
./hsh

​ 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:

$./hsh
$

​ 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'
$

​

Environment 🌳

​ 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: ​

HOME

The home directory of the current user and the default directory argument for the cd builtin command. ​

$ echo "echo $HOME" | ./hsh
/home/vagrant

​

PWD

The current working directory as set by the cd command. ​

$ echo "echo $PWD" | ./hsh
/home/vagrant/holberton/simple_shell

​

OLDPWD

The previous working directory as set by the cd command. ​

$ echo "echo $OLDPWD" | ./hsh
/home/vagrant/holberton/printf

​

PATH

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. ​

$ echo "echo $PATH" | ./hsh
/home/vagrant/.cargo/bin:/home/vagrant/.local/bin:/home/vagrant/.rbenv/plugins/ruby-build/bin:/home/vagrant/.rbenv/shims:/home/vagrant/.rbenv/bin:/home/vagrant/.nvm/versions/node/v10.15.3/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin:/home/vagrant/.cargo/bin:/home/vagrant/workflow:/home/vagrant/.local/bin

​

Command Execution 🔪

​ 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 variablefor 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. ​

Exit Status 👋

​ 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). ​

Signals ❗

​ 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
$

​

Variable Replacement 💲

​ hsh interprets the $ character for variable replacement. ​

$ENV_VARIABLE

ENV_VARIABLE is substituted with its value. ​ Example:

$ echo "echo $PWD" | ./hsh
/home/vagrant/holberton/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

​

Comments #️⃣

​ 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'

​

&& - AND logical operator

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'

​

|| - OR logical operator

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 ;. ​

hsh Builtin Commands 🔩

​

cd

• 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/vagrant/holberton/simple_shell
$ cd ../
$ pwd
/home/vagrant/holberton
$ cd -
$ pwd
/home/vagrant/holberton/simple_shell

​

alias

• 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_1.c      error.c             input_helpers.c        scanner.c       shell.h       
README.md            builtins_2.c      error_funct.c       man_1_simple_shell     sh_help.c       shunt.c
alias_builtins.c     env_builtins.c    error_funct_1.c     node.c                 sh_help_1.c     string1.c
builtins.c           environs.c        getline.c           proc_file_comm.c       shell.c         string2.c

​

exit

• 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

​

env

• Usage: env
• Prints the current environment. ​ Example:

$ ./hsh
$ env
NVM_DIR=/home/vagrant/.nvm
...

​

setenv

• 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

​

unsetenv

• Usage: unsetenv [VARIABLE]
• Removes an environmental variable.
• Upon failure, prints a message to stderr. ​ Example:

$ ./hsh
$ setenv NAME Poppy
$ unsetenv NAME
$ echo $NAME
​
$