Bash shell configuration files

Then why do we have two different configuration files? Well, the short answer is freedom and convenience. The longer answer is as follows: Suppose, You wish to run a system diagnostic every time you log in to your Linux system.

You can edit the configuration file to print the results or save it in a file. But you only wish to see it at startup and not every time you open your terminal. This is when you need to use the. Shells are one of, if not the most powerful tools available to a Linux user. Without shells, it is practically impossible for a person to utilise the features and functionality offered by the kernel installed on their system.

With the bash shell configuration files such as. It can help us make our work efficient and easier. We hope this tutorial was able to help you to get understand the concept the. If you have any feedback, queries or suggestions, feel free to reach out to us in the comments below. The main disadvantages are security, if someone can alter the config file then they can execute code, and it is harder to make it idiot proof.

The advantages are speed, on a simple test it is more than 10, times faster to source a config file than to run pq, and flexibility, anyone who likes monkey patching python will appreciate this. Usually only a few 1 to 3 values. If you are using eval to set multiple values then you are executing selected parts of the config file No need to eval anything.

The performance hit of using a standard format with an existing parser even though it's an external utility is negligible in comparison to the robustness, the amount of code, the ease of use, and maintainability. Show 3 more comments. NFarrington NFarrington 87 2 2 bronze badges.

I had high hopes for that article came up in my search results too , but the author's suggestion of attempting to use regex to filter out malicious code is an exercise in futility. The procedure with dot, requires an absolute path? With the relative one it doesn't work — Davide.

Asclepius 3 3 silver badges 7 7 bronze badges. Isn't this supposed to first create the config file if it doesn't exist? This is succinct and secure: Read common vars from common. Tested on mac with bash, i.

Marcin Marcin 2 2 gold badges 5 5 silver badges 13 13 bronze badges. Just see how evil1 and evil2 files are created if you put this to common. Running on mac. I've tried env -i However, if you remove "garbage", it will work. So thanks for explaining. Asclepius Asclepius 3 3 silver badges 7 7 bronze badges.

It's also compliant with bash --posix. See bottom for test. But sh doesn't support it because of declare. Basic test for those who want proof Create file evil. Yuri Pozniak Yuri Pozniak 4 4 bronze badges. Iiridayn Iiridayn 3 3 silver badges 12 12 bronze badges.

Sign up or log in Sign up using Google. Which one is the best or may be there are some better ways to do that? I want to do that in pure Bash it's easy in PHP for example. BTW, how do I redirect output to external file here? Do I need to escape something if variables contain, say, quotes? Seems bad to me because of the need to escape many different symbols and with many variables the line will be tooooo long.

Try envsubst. I have a bash solution like mogsie but with heredoc instead of herestring to allow you to avoid escaping double quotes. I think eval works really well. It handles templates with linebreaks, whitespace, and all sorts of bash stuff.

If you have full control over the templates themselves of course:. This method should be used with care, of course, since eval can execute arbitrary code. Running this as root is pretty much out of the question. Quotes in the template need to be escaped, otherwise they will be eaten by eval.

Edit: Added comment about how quotes need to be escaped, added plockc's solution to the mix! I needed to keep double quotes in my configuration file so double escaping double quotes with sed helps:.

Instead of reinventing the wheel go with envsubst Can be used in almost any scenario, for instance building configuration files from environment variables in docker containers. If on mac make sure you have homebrew then link it from gettext:. If you want to use Jinja2 templates, see this project: j2cli. Here is another solution: generate a bash script with all the variables and the contents of the template file, that script would look like this:.

Taking the answer from ZyX using pure bash but with new style regex matching and indirect parameter substitution it becomes:. If using Perl is an option and you're content with basing expansions on environment variables only as opposed to all shell variables , consider Stuart P. Bentley's robust answer. This answer aims to provide a bash-only solution that - despite use of eval - should be safe to use. Here is an improved version of the bash-only, eval -free solution from the accepted answer :.

Perfect case for shtpl. But here is the solution it offers anyhow. May you want to test it. This page describes an answer with awk. This is the pure bash function adjustable to your liking, used in production and should not break on any input. If it breaks - let me know. To follow up on plockc's answer on this page, here is a dash-suitable version, for those of you looking to avoid bashisms.

Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Collectives on Stack Overflow. The first command connects to the remote system and opens an interactive shell only. In contrast, the second command connects to the remote system, executes the given command in a non-interactive login shell, and terminates the ssh connection. The example below shows this in more detail:.

In order to find out if you are logged into your computer using a login shell, type the following echo command in your terminal:.

For a non-login shell, the output is just the name of the shell. Regarding the configuration for this type of shell, three files are taken into account. See below for a detailed description of these files. This mode describes opening a new terminal, for example, xterm or Gnome Terminal, and executing a shell in it.

This mode is in use when executing a shell script. The shell script runs in its own subshell. It is classified as non-interactive unless it asks for user input. The shell only opens to execute the script and closes it immediately once the script has terminated.

This mode covers logging into a computer from a remote, for example, via Secure Shell ssh.