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Useful Commands

This is a collection of useful linux commands that can be easily copy pasted.

General

Replacing lines in a file 

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sed -i 's/^key_in_file=.*$/key_in_file=new_value/' ./path/to/my_file.txt
This will iterate over all lines of ./path/to/my_file.txt and apply the specified changes. In this case these changes are the value of the key_in_file key. The sed command can also be used to apply the same changes to outputs of other functions.

Extract values from JSON files 

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MY_VARIABLE=$(jq -r '.version' path/to/my/file.json)
The jq package is a useful utility for processing .json files. Make sure to install it before attempting to use the above command. As mentioned on the webpage jq is like sed for JSON data.

GIT

View all remotes 

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git remote -v

Change remote URL of specific remote 

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git remote set-url remote_name new_url
This can be useful if you for example moved your repository to a new domain / git platform or if you want to change the way you interact with a repository (e.g. change from ssh to https).

Add a new remote 

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git remote add remote_name https://my.gitlab.instance/user/project.git
In some cases you may wish to add a second remote. For example in cases where your code is stored on multiple git platforms that you wish to keep in sync.

Push to a specific remote 

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git push -u -f remote_name

Revert already pushed commits 

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# Assuming last commit was commit 5 and the one before was commit 4 and then 3 et.
# We want to undo the last two commits
git revert <commit_hash_5>
git revert <commit_hash_4>
# Push the reverts to your brachn
git push

CRON

The cron command-line utility is a job scheduler on Unix-like operating systems 1. It can be used to periodically run various scripts on your server. A detailed CRON guide is provide by DigitalOcean. A helpful utility for understanding the cron time settings can be found on the following link: https://crontab.guru

Editing the crontab of the current user: 

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crontab -e

Erasing the crontab of the current user: 

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crontab -r

Storing the output of a cron job to a log file: 

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*/1 * * * * bash /path/to/your/command_or_script >> /path/to/cron_output.log 2>&1

Info

In some environments you may need to setup environment variables such as the PATH and the DOCKER_HOST. This will enable your cron scripts to access and interact with services such as docker.

Tip

Ensure that you terminate commands with new lines and escape percentage signs using a backslash \% as this may cause issues if it is not done.

  1. https://en.wikipedia.org/wiki/Cron ↩