ShellCommandBuilder

Creating basic and more complex shell commands in an fluid object-oriented fashion. This makes it very straight forward to abstract the general mechanisms of bash behind a readable and debuggable layer.

The Reference for this library is based on the GNU Bash Reference Manual
If you need more features from that reference in this library, feel free to create an issue or pull request.

Concept

Imagine you want to create the following bash command: a && b | c || d |& f && (g && h) || {i || j;}

You can achieve that by creating a ShellBuilder-Object and then reading the command from left to right as instructions.

<?php

use PHPSu\ShellCommandBuilder\ShellBuilder;

$builder = new ShellBuilder();
$builder
    ->add('a')
    ->and('b')
    ->pipe('c')
    ->or('d')
    ->pipeWithForward('f')
    ->and(
        $builder->createGroup()->add('g')->and('h')
    )
    ->or(
        $builder->createGroup(true)->add('i')->or('j')
    );

Table of Contents

1. Installation
2. Usage
   1. Simple Commands
   2. Pipelines, Lists, and Redirections
   3. Complex Commands
   4. Conditional Expressions
   5. Coprocess
3. Specials
4. Contributing
5. Testing

Installation

You can use this library in your project by adding it with composer:

composer require phpsu/shellcommandbuilder

Then include it in your class/file.

<?php

use PHPSu\ShellCommandBuilder\ShellBuilder;

$builder = new ShellBuilder();

Introduction

This library is boiled down to these three main components:

• ShellBuilder
• ShellCommand
• ShellWord

The ShellBuilder is the glue that holds a collection of commands together. The glue is one of the control operators like || or &&.
Commands are represented by the ShellCommand-Class. The ShellCommand is responsible for the arguments and options etc.
A ShellCommand is composed of ShellWords, they represent the tokens that make up a command.

Let's look at an example:

echo "hello world" | grep -e "world"

This entire line is a ShellBuilder-Object containing the two ShellCommands:

• echo "hello world
• grep -e "world"

Those are connected with the |-Operator
Taking apart each of those commands returns the following ShellWords:

executable	arguments	options
echo, grep	hello world	-e "world"

Usage

Simple Commands

Much of the API is marked internal, it is meant to be accessed through the ShellBuilder-Class.
This should make it very straight-forward to build simple and more complex commands from one basis.
Additionally, the ShellBuilder has factory-style methods that help building commands top to bottom in an instant.

That means, creating a ShellBuilder can look like this:

$builder = new ShellBuilder();

or like this:

$builder = ShellBuilder::new();

A ShellCommand can be created like this:

$command = ShellBuilder::command('name-of-command');

or, if there is already a ShellBuilder-object available, like this

/** @var \PHPSu\ShellCommandBuilder\ShellBuilder $builder */
$builder->createCommand('name-of-command');

Let's take a look at the command from earlier and build it step by step.

echo "hello world" | grep -e "world"

Note: each step is written into the code as comment

<?php
use PHPSu\ShellCommandBuilder\ShellBuilder;


// 1. First we create the command `echo`
$echo = ShellBuilder::command('echo');

// 2. "hello world" is an argument, that we can add like this:
$echo->addArgument('Hello World');

// 3. we create the `grep` command
$grep = ShellBuilder::command('grep');

// 4. and add the option '-e "world"'.
// the single hyphen that is before the option "e" marks it as a *short* option (addShortOption)
// Having two hyphens like --color makes it a regular option (addOption)
$grep->addShortOption('e', 'world');

// 5. Now we need combine those two commands together
// We do that, by creating a ShellBuilder
$builder = ShellBuilder::new();

// 6. And then adding the echo-command into it
$builder->add($echo);

// 7. Earlier we saw, that these two commands where held together by the pipe-Operator
// This can be accomplished by using the pipe-Method 
$builder->pipe($grep);

// 8. To use this command in e.g. shell_exec, you can convert it into a string and use it
shell_exec((string)$builder); // -> echo 'hello world' | echo -e 'world'

Note: Every argument and option is escaped by default.

All methods implement the fluent interface. For this library that means that you can rewrite the example above by chaining everything together:

<?php

use PHPSu\ShellCommandBuilder\ShellBuilder;

$builder = ShellBuilder::new()
    ->createCommand('echo')
    ->addArgument('Hello World')
    ->addToBuilder()
    ->pipe(
        ShellBuilder::command('grep')
            ->addShortOption('e', 'world')            
    );
shell_exec((string)$builder); // -> echo 'hello world' | echo -e 'world'

The createCommand passes the current ShellBuilder into the ShellCommand-Instance. Through addToBuilder that ShellBuilder can be accessed again, and the command is automatically added to the ShellBuilder. This currently only works for and.

Pipelines, Lists, and Redirections

The ShellBuilder is a representation of what holds commands together. Whether it is to execute commands sequentially, or to connect input and output.

Let's look at this following fake example:
a; b && c | d || e |& f 2>&1
It illustrates the various ways of connecting commands together.

Rebuilding this command could look like this:

<?php

use PHPSu\ShellCommandBuilder\ShellBuilder;

$builder = new ShellBuilder();
// adding the initial command
$builder->add('a');
// adding the next command for `;`
$builder->add('b');
// combining with and --> `&&` 
$builder->and('c');
// piping the output --> `|`
$builder->pipe('d');
// combining with or --> `||`
$builder->or('e');
// piping the output including the error --> `|&`
$builder->pipeWithForward('f');
// redirect stderr to stdout --> `2>&1`
$builder->redirectErrorToOutput();

The full list of methods can be found here: API Docs

Complex Commands

The idea behind this library is to make generating larger and complex shell commands more readable and maintainable.
The following example is taken out of PHPsu. This command syncs a database from a remote source to a local database.

ssh -F 'php://temp' 'hostc' 'mysqldump --opt --skip-comments --single-transaction --lock-tables=false -h '\''database'\'' -u '\''root'\'' -p '\''root'\'' '\''sequelmovie'\'' | (echo '\''CREATE DATABASE IF NOT EXISTS `sequelmovie2`;USE `sequelmovie2`;'\'' && cat)' | mysql -h '127.0.0.1' -P 2206 -u 'root' -p 'root'

First, we have to think about the components that this command is composed of. This results in these commands:

ssh -F 'php://temp' 'hostc'

mysqldump --opt --skip-comments --single-transaction --lock-tables=false -h 'database' -u 'root' -p 'root' 'sequelmovie'

echo 'CREATE DATABASE IF NOT EXISTS `sequelmovie2`;USE `sequelmovie2`;'

cat

mysql -h '127.0.0.1' -P 2206 -u 'root' -p 'root'

Now, we build this in PHP:

<?php

use PHPSu\ShellCommandBuilder\ShellBuilder;

$builder = new ShellBuilder();
// creating the first command.
// The 'true' removes the connection between ShellBuilder and ShellCommand and makes it anonymous.
// This is the same result as ShellBuilder::command()
$mysqlDump = $builder->createCommand('mysqldump', true)
// adding the options and short-options
    ->addOption('opt')
    ->addOption('skip-comments')
    ->addOption('single-transaction')
// the signature of options have four variables
// 'lock-tables' is the name of the option --> "--lock-tables"
// the string 'false' is the value --> "--lock-tables 'false'"
// the third variable disables escaping --> "--lock-tables false"
// the fourth variable turns the space between name and value into '=' --> "--lock-tables=false"
    ->addOption('lock-tables', 'false', false, true)
    ->addShortOption('h', 'database')
    ->addShortOption('u', 'root')
    ->addShortOption('p', 'root')
    ->addArgument('sequelmovie')
    ->addToBuilder();
$builder->createCommand('ssh')
    ->addShortOption('F', 'php://temp')
    ->addArgument('hostc')
// SubCommand is technically an argument, that always escapes the output
    ->addSubCommand(
        $mysqlDump->pipe(
// 'createGroup' flags a ShellBuilder to wrap the commands in braces e.g (echo "hello world")
            $mysqlDump->createGroup()
            ->createCommand('echo')
            ->addArgument('CREATE DATABASE IF NOT EXISTS `sequelmovie2`;USE `sequelmovie2`;')
            ->addToBuilder()
            ->and('cat')
        )
    )
    ->addToBuilder()
    ->pipe(
        $builder->createCommand('mysql')
            ->addShortOption('h', '127.0.0.1')
// disabling escaping here: --> "-P 2206"
            ->addShortOption('P', '2206', false)
            ->addShortOption('u', 'root')
            ->addShortOption('p', 'root')
    )
;

Next, we take a look at how to achieve process and command substition. The following is again a mock example. It creates a list of all php-files in the current and all below directories, sorted and enriched with the size. This file-list is redirected into a txt-file with the current month-name as filename.

cat <(ls -1ARSsD | grep ".*\.php") >> $(date +%B).txt

And this is how it could look like in php:

use PHPSu\ShellCommandBuilder\ShellBuilder;

$builder = ShellBuilder::new()
    ->createCommand('cat')
// the false at the end prints the argument unescaped
    ->addArgument(
        ShellBuilder::new()
// turning all commands within this builder into a process substitution --> <(command ...)
// the same would work with `createCommandSubstition` resulting in something like this $(command ...)
        ->createProcessSubstition()
        ->createCommand('ls')
// currently combining short-options has to be done manually, although it could change in the future
// but doing it like this will always be possible, since it's impossible to evaluate the correctness
// without having the man-page of all the commands available
        ->addShortOption('1ARSsD')
        ->addToBuilder()
        ->pipe(
            ShellBuilder::command('grep')
            ->addArgument('.*\.php')
        ),
        false
    )
    ->addToBuilder()
// redirects stdout from the previous command and pushes it into stdin of the next command
// if redirected into a file, the true at the end changes the type to appending instead of overwriting --> "a >> b"
    ->redirectOutput(
        ShellBuilder::new()
            ->createCommand('date')
            ->addArgument('+%B', false)
// this is similar to the process/command-substitition from above but here it is applied on a command instead
// toggling means that instead of taking true or false as an argument it flips the internal state back and forth
            ->toggleCommandSubstitution()
            ->addToBuilder()
            ->addFileEnding('txt'),
        true
    )
;

Conditional Expressions

Conditional Expressions are currently a work in progress. The basic API stands, but the overall usage might change, especially when it comes down to escaping.

There are multiple conditional-expression-types that can be used to built expressions. They are build upon the Shell-Syntax Bash Reference.

The following expression-types exist:

• Artihmetic: ArithmeticExpression::class
• File: FileExpression::class
• Shell: ShellExpression::class
• String: StringExpression::class

Let's look at two examples:

• 1: Only executing a command, if a file is not empty
• 2: Only executing a command, if a variable is greater than 5

# 1:
[[ -s test.php ]] && echo "hello";

# 2: 
a=6; [[ "$a" -gt "5" ]] && echo "hello";

# 3: 
a=`cat file.txt`; [[ "$a" -gt "5" ]] && echo "hello";

use PHPSu\ShellCommandBuilder\ShellBuilder;
use PHPSu\ShellCommandBuilder\Conditional\FileExpression;
use PHPSu\ShellCommandBuilder\Conditional\ArithmeticExpression;

# 1:
ShellBuilder::new()
    ->add(FileExpression::create()->notEmpty('test.php'))
    ->and(ShellBuilder::command('echo')->addArgument('hello'))
;

# 2:
ShellBuilder::new()
    // adding a variable "a" with the value "6"
    // the third argument replaces $() through backticks --> a=$(cat) ~> a=`cat`
    // the fourth argument sets escpaing to false.
    // Escaping is disabled for commands as value.
    ->addVariable('a', '6', false, false)
    ->add(ArithmeticExpression::create()->greater('$a', '5'))
    ->and(ShellBuilder::command('echo')->addArgument('hello'))
;

# 3:

ShellBuilder::new()
    ->addVariable('a',
        ShellBuilder::new()
        ->createCommand('cat')
        ->addNoSpaceArgument('file')
        ->addToBuilder()
        ->addFileEnding('txt'),
        true // enable backticks
    )
    ->add(ArithmeticExpression::create()->greater('$a', '5')->escapeValue(true))
    ->and(ShellBuilder::command('echo')->addArgument('hello'))
;

Coprocess

To run commands in the background, the ShellBuilder class supports the coproc keyword.
This keyword lets the command run asynchronously in a subshell and can be combined with pipes and redirections.

More information on Coprocesses can be found in the Bash Reference.

Let's look at an example: {coproc tee {tee logfile;} >&3 ;} 3>&1
This starts tee in the background and redirects its output to stdout

use PHPSu\ShellCommandBuilder\Definition\GroupType;
use PHPSu\ShellCommandBuilder\ShellBuilder;

// we first create a new ShellBuilder, that will be wrapped in the group-syntax that does not open a subshell
// -> { command-list ;}
$builder = new ShellBuilder(GroupType::SAMESHELL_GROUP);
// then we set that builder to be asynchronous.
// the second argument of this method gives the coprocess a name.
// default is no name
// -> coproc [NAME] command
$builder->runAsynchronously(true)
    ->createCommand('tee')
    ->addArgument(
// createGroup again wraps it into a group-syntax and the true indicates, that is is in the same-shell notation
// false would open a subshell like e.g ( command ).
// default is false
        $builder->createGroup(true)
            ->createCommand('tee')
            ->addArgument('logfile', false)
            ->addToBuilder(),
        false
    )
    ->addToBuilder()
// redirectDescriptor is the more powerful way of writing redirects between File Descriptors
// argument 1: command that we redirect from/to
// argument 2: direction of the redirect (true: >&, false <&)
// argument 3: file descriptor before redirection
// argument 4: file descriptor after redirection
// the example below would render: >&3
    ->redirectDescriptor('', true, null, 3);
ShellBuilder::new()->add($builder)->redirectDescriptor('', true, 3, 1);            

If you want to direct a single command or a list of commands into the background, you can achieve that by appending an ampersand & at the end of a command.

So maybe you want to do this: ./import-script & ./import-script2 &

Then, this can be achieved like this:

<?php
use PHPSu\ShellCommandBuilder\ShellBuilder;

ShellBuilder::new()->add('./import-script')->async('./import-script2')->async();

Special

Pattern-Class - ShellWord parsing

The pattern-class validates string inputs as valid Bourne Shellwords. It is based on its equivalent implementations in the Ruby and Rust languages.
It takes a string and applies the word parsing rules of shell to split it into an array.

use PHPSu\ShellCommandBuilder\Definition\Pattern;

Pattern::split('three blind mice');
// ['three', 'blind', 'mice']

Pattern::split respects escaping and quoting and only splits outside of these:

use PHPSu\ShellCommandBuilder\Definition\Pattern;

Pattern::split('/home/user/dev/hallo\ welt.txt');
// ['/home/user/dev/hallo welt.txt']

Pattern::split('a "b b" a');
// ['a', 'b b', 'a']

The method will throw an exception if there is an invalid input.
For example the following has an unmatched quoting:

use PHPSu\ShellCommandBuilder\Definition\Pattern;
Pattern::split("a \"b c d e");
// ShellBuilderException::class
// The given input has mismatching Quotes

Debugging the ShellBuilder

Sometimes there is a need to better understand why the output is rendered the way it is.
For those situations, all classes implement a __toArray()-method, that take the current class-state and print it as an array. The ShellBuilder additionally implements jsonSerializable. It itself calls the __toArray-method and is meant as a shortcut for outputting to a client.

If you call __toArray() on a ShellBuilder, it will go through all commands and turn them into an array too. That way you have a deeply nested structure, that represents the list of commands you want to execute.

Contributing

install for contributing

git clone git@github.com:phpsu/ShellCommandBuilder.git
cd ShellCommandBuilder
composer install

Testing

composer test

You can also check, whether any changes you made are affecting your tests immediately on save:

composer test:watch

Type-Checking is being done with psalm.

composer psalm

If you see a low Mutation Score Indicator (MSI) value, you can show the mutations that are escaping:

composer infection -- -s

Security

Email git@cben.co if you discover any security related issues.

Credits

• Chris Ben
• Matthias Vogel

License

The MIT License (MIT). Please see License File for more information.