Automation Gateway provides a Script Execution Engine that allows for the decoration and execution of scripts written in any language including Python, Perl, and Bash. Users determine the scripts being managed by providing a list of directory paths in their properties.yml configuration file. A recursive search of the directory paths is performed. Once a script has been discovered, it is available to be decorated. The decoration of scripts within Automation Gateway is similar to that of Ansible playbooks.
However, instead of decorating the variables within a playbook, users decorate the command line arguments and environment variables utilized to execute a script. A permanent copy of each script's decoration is stored in a local database that is maintained by Automation Gateway. Scripts that have been decorated can be executed either locally or on a remote set of hosts. Decorating a script involves creating metadata in a JSON file format that describes the command line arguments and environment variables used to execute a script. The metadata is more specifically known as a JSON schema. Not surprisingly, the format of the flags and arguments that make up a script's command line can vary significantly from script to script.
To help users with the decoration process, Automation Gateway provides a low-level schema that serves as a template for creating script specific schemas. Based on their knowledge of the script, users identify the parameters that will compose the script's schema. At a low level, parameters are JSON objects with type and description fields.
All parameters are considered to be either a string or an array of strings. If a script has a minimum set of parameters that are needed for successful execution, the required field can be added to the decoration. In practice, it requires the sys module to process input data properly. To do so, both the sys module and the getopt module have to be loaded beforehand. Next, from the list of input parameters we remove the first list element , and store the remaining list of command line arguments in the variable called argument_list. Complex tools like this are typically controlled by the user via command line arguments, which allows the user to use specific commands, set options, and more.
For example, these options could tell the tool to output additional information, read data from a specified source, or send output to a certain location. Another benefit of command-line arguments is the additional security that comes with it. Let's say we have a program to save data into the database. If we store the database credentials in the script or some configuration file, it can be accessed and executed by anyone having access to the files. But, if the user/password is provided as a command-line argument, then it's not present in the file system and our program is more secured. This can be done via the Automation Gateway UI or by a separate application.
Scripts can either be executed on the host the AG server is running or on a set of remote hosts. The API returns an array of objects, each containing results for the host upon which the script was executed. The first index of the array consists of the python script file name. And from the second position, you'll have the command line arguments passed while running the python script.
In every shell script, there is a collection of numbered variables, which are generally referred to as $1, $2, etc. These are the "positional parameters", more commonly known as the command line arguments. You can think of these as variables named 1, 2, etc. and to get their values, you would use $1, $2, etc. When you call a script named my_script via the command line ./my_script a b c, it would get three arguments which are stored in the three variables $1, $2, and $3. You cannot assign to these variables , but you can examine and use their values.
For example, echo "$1" would print the first argument to your script. This article explores these two methods for getting data into the script and controlling the script's execution path. Make a new file with the name "Check.sh" in your home directory. Add the same bash script as shown in the below image.
In this script, we have a variable "var" to store the argument value passed by the user. Then we have an "if" statement, which will check for the argument value to be matched or not. If the argument value is matched with the value provided in the parenthesis, then the first "echo" statement will be executed.
If the value does not match, the second "echo" statement will be executed. Supports the passing of parameters to scripts even when you run them from a command line. You can pass a single parameter, multiple parameters, parameter and value pairs for multiple parameters, and even lists. Parameter values are passed as text strings to the script immediately preceding them.
Keep this in mind if you are running multiple scripts in a command. Note that the 0th argument is the name of the PHP script that is run. The rest of the array are the values passed in on the command line.
This approach works, but it is very simplistic and doesn't play well if you're looking to transition from a query parameter way of passing in values to your script. With this approach there is no way to give names the the command line arguments being passed in. You added a help function and the ability to process command line options to display the help selectively.
And you added an optional argument that allows entering a name on the command line. The getops command reads any and all options specified at the command line and creates a list of those options. The while command loops through the list of options by setting the variable $options for each in the code below. The case statement is used to evaluate each option in turn and execute the statements in the corresponding stanza. The while statement will continue to assess the list of options until they have all been processed or an exit statement is encountered, which terminates the program.
The following were the process and specification of passing and parsing the variables in the bash script. The logic of shifting and making modifications to the variables is in the hands of the user. This was just a demonstration of passing in and parsing down the arguments from the command line to the script to make them more dynamic. The above screenshot displays the parameters passed to the script, how we'll do that, which we'll explain in the next section. But right now we can see we have passed in the parameters from outside of the script using bash environment variables. You can even use strings and other data types but beware of any whitespace.
White space will make the variable a separate parameter. So, for strings especially, be careful to strictly surround them with quotation marks. Parsing and Passing of Arguments into bash scripts/ shell scripts is quite similar to the way in which we pass arguments to the functions inside Bash scripts.
We'll see the actual process of passing on the arguments to a script and also look at the way to access those arguments inside the script. Open this newly created file and add some bash script to it. I have added some default variables, e.g. "$1", "$2", and "$3" consequently. Whatever arguments will be passed through the terminal will be stored in the stated variables. Most of the Linux Mint 20 Users find themselves stuck when passing an argument in a bash script. You can pass the arguments to any bash script when it is executed.
There are several simple and useful ways to pass arguments in a bash script. In this article guide, we will let you know about some very easy ways to pass and use arguments in your bash scripts. In this second example we simply count the number of command line arguments using the built-in len() method. Thus, the actual number of arguments passed by the user is len(sys.argv) - 1. We can use "@" variable to access every parameter passed to the script via the command line.
It is a special variable that holds the array of variables in BASH. In this case, we are using it alone, so it contains the array of positional parameters passed in. We can use it to iterate over the parameters passed using loops or while loop as well. We can pass parameters just after the name of the script while running the bash interpreter command. Just the command for running the script normally by adding the value of the parameters directly to the script. Every parameter is a space-separated value to pass to the shell script.
Python 3 supports a number of different ways of handling command line arguments. In terms of names, and its usage, it relates directly to the C library . The second way is the getopt module, which handles both short and long options, including the evaluation of the parameter values.
By default, scripts are executed from the home directory of the user that owns the Automation Gateway server process. To change the default execution directory, add the working_dir key to the script's schema outside the properties object. The value of working_dir can be an absolute or a relative directory path. Each script being managed by Automation Gateway includes an env_vars parameter within its default schema. All environment variable decorations for a script must be contained within the env_vars object. Any parameter residing outside of env_vars will be treated as a script argument.
The default schema also includes the parameter env_list as a member of the env_vars object. The env_list parameter is of type array and allows variables to be passed to a script as if they were being entered directly on the command line within the Linux shell. As with every shell application, the PHP binary accepts a number of arguments; however, the PHP script can also receive further arguments. The number of arguments that can be passed to your script is not limited by PHP . The arguments passed to the script are available in the global array $argv. The first index always contains the name of the script as called from the command line.
The same is true if the code is executed via a pipe from STDIN. There you have it - an array containing any arguments you passed in. Notice the first two elements - node and the path to your script. In this write-up, we have learned how to pass arguments through the command line to a bash script. Command-line arguments help us write dynamic scripts which perform different functions depending on the input.
Use the parameter /stdout to enable streaming files to the standard output of winscp.com. When the parameter is used, the get command will stream the downloaded file to the standard output, when - is used as a download target. With the chunked flag, the files are individually encoded using Chunked transfer encoding, what allows separating contents of multiple streamed files. When the parameter is used, all console output that would normally be printed to the standard output is redirected to the error output. Instead, Bash functions work like shell commands and expect arguments to be passed to them in the same way one might pass an option to a shell command (e.g. ls -l). In effect, function arguments in Bash are treated as positional parameters ($1, $2..$9, $, $, and so on).
The variable is the array of all the input parameters. Using this variable within a for loop, we can iterate over the input and process all the arguments passed. Our third example outputs every single argument sent to the Python script, except the program name itself. Therefore, we loop through the command line arguments starting with the second list element. Recall that this is index 1 since lists are 0-based in Python.
Automation Gateway passes environment variables to scripts executed on the local host via the script API /scripts//execute. The contents of the variables are included within an env object in the same way script arguments are included using the args object. Like script arguments, environment variables can be decorated by including them in a script's schema. Each script being managed by Automation Gateway has a default schema. The schema consists of the parameters argument_list and env_vars. A description of the env_vars parameter can be found in the Decorating Environment Variables section later on in this document.
That's what happens when you attempt to expand a shell parameter that is not defined. You'll notice, further, that when more command-line arguments are passed, the ones past the third are not used. That's probably what you'd expect, since the script doesn't refer to them at all. In the case of your -h option, you want the program to print the help text to the terminal session and then quit without running the rest of the program. The ability to process options entered at the command line can be added to the Bash script using the while command in conjunction with the getops and case commands. Arguments passed to a Bash script follow the name of the script in the command line and they are separated from each other by a space.
Each argument can be referenced in the script by positional parameters defined by default in Bash ($1, $2, $3, etc…). We can print the arguments passed to the script by a simple powerful variable '@' which stores all the parameters passed. Using getopts, we can assign the positional arguments/ parameters from the command line to the bash variables directly. This allows us to manage the parameters nicely and in a systematic way. In the above script, we have used two arguments to store the bash variables using the getopts syntax, while loops and switch-case statements.
We are using the variable '#' as it holds the number of parameters passed in. We initialize the number of parameters and take away one as we are going to use an array to iterate over it. As this array is initialized from the last element or parameter passed, we need to decrement the counter until 0 to print every parameter in the order it is passed.
We simply use the BASH_ARGV array to access the parameters and print its value. Also, at every iteration, we decrease the value of i- the iterator or counter by one using the arithmetic double braces. From this, we simply print every parameter passed to the script using a while loop as shown from the output screenshot.
With this script, we can detect whether any positional parameters were passed in or nothing was passed. The -z flag checks for any NULL or uninitialized variables in BASH. The -z flag returns true if the variable passed is NULL or uninitialized.
