if i install an app x with apt install x, how can i reference this app later on to change one of its params in bash

To modify parameters of an installed application using Bash after installing it with apt, you generally need to identify the configuration file associated with that application or use specific command-line options provided by the app. Below, we delve into the methods to reference and change parameters for an application installed via apt.

Understanding Package Configuration

When you install an application using apt install x, several things occur:

• The application is downloaded and installed, often with dependencies.
• Configuration files may be generated and placed in standard directories like /etc/, where they can be modified as needed.

Typically, applications have their configuration files located in /etc/<package-name>/ or sometimes within a subdirectory of this path. For example, if you installed nginx, its configuration file might be located at /etc/nginx/nginx.conf.

Finding Configuration Files

1. Location of Configuration Files

Most applications have associated configuration files located in the following typical directories:

• Global configuration: /etc/<application-name>/
• User-specific configuration: ~/.config/<application-name>/

You can search for the configuration files using:

dpkg -L <package-name> | grep config

This command lists all files installed by the package, filtered to show those likely containing configurations.

2. Modifying Parameters

Once you locate the configuration file, you can modify it using a text editor like nano, vim, or gedit. Here’s how you can do this:

sudo nano /etc/<application-name>/<config-file>

After making your changes, save the file and exit the editor.

Using Command-Line Options

Alternatively, many applications allow parameters to be changed directly through command-line options. For instance, many servers or daemons can start with different parameters like port numbers, paths, or modes. You can reference the app in a Bash script with both the name of the app and its options.

Example

If you are manipulating a service, you can run:

sudo systemctl restart <service-name>

Or if it allows custom parameters, adjust accordingly, like so:

<application-name> --option value

Scripting Changes

To automate changes, you can create a Bash script. For instance, if you want to change a value in a configuration file regularly, you could write a script like this:

#!/bin/bash
# Script to update nginx config

# Backup the current config file
sudo cp /etc/nginx/nginx.conf /etc/nginx/nginx.conf.bak

# Update the server name (as an example)
sudo sed -i 's/old.server.name/new.server.name/' /etc/nginx/nginx.conf

# Reload the service to apply changes
sudo systemctl reload nginx

This script backs up the original config file, modifies a parameter, and reloads the service to apply the changes.

Conclusion

Referencing and modifying parameters of installed applications in Bash is primarily done through configuration files or application-specific command options. Identifying the configuration files using dpkg -L allows you to access and edit them securely. For repetitive tasks, automating changes with Bash scripts is an effective approach.

This method not only simplifies management but also ensures changes are consistently applied. If you need further details on a specific application, please let me know!