mentels/TIL

Today I Learned

TIL

My personal Today I Learned inspired by jbranchaud/til

This a collection of small things that I learn on daily basis in the software engineering world. This is not only a record of my journey through tech but also a way to capture stuff that I find useful and don't want to forget. Finally, it's about practising writing.

89 TIL and counting...

Categories

• TIL
  • Categories
  • Ansible
  • Awk
  • Curl
  • Docker
  • Elixir
  • Erlang
  • Git
  • GPG
  • JavaScript
  • Linux
  • Make
  • PostgreSQL
  • RabbitMQ
  • Sed
  • Shell
  • SSL/TLS
  • Vim

---

Ansible

• Tell jinja2 not to template data
• Repeat task until certain criteria is met

Awk

• Print CSV file fields based on other fields properties

Curl

• Request an URL with basic auth
• PUT/POST JSON

Docker

• Get IP address of a container

Elixir

• Stream between files
• Regex to match several things in no particular order
• Limit and control the output of IO.inspect/2-3
• Row-level locking
• Testing macros with Code.eval_string/3
• nil can give unexpected results combined with the Access protocol
• Use with to pattern match only on a success case
• Skip a test in ExUnit
• Find Erlang/OTP version for a BEAM file

Erlang

• Parse Code as String and Evalute it
• Fix shell after killing rebar3 shell
• Matching signed integers uses Two's complement

Git

• Show git history with only your commits (skipping merges)
• Effectively clone with long history
• Ignore local changes to files with update-index
• print-only-commit-summar
• See diff (checkout) for a single file between branches
• See diff between stashes (also for a single file)
• Use multiple keys for single Github account
• Revert commit without commiting
• Handle deleted by us/them in rebase
• Print files from a commit
• Update branch after force push
• Revert merge commit
• Turn object reference into SHA-1 (e.g. HEAD)
• Choose version of a file when both added
• List untracked files
• Copy current branch to the clipboard
• Checkout previous branch
• Grep commit message or contents
• Remove remote git tag
• List all modified files
• Checkout a file from another branch
• Undo rebase
• Work with multiple branches at a time
• Fixup and Autosquash
• Stage only deleted files
• Add only untracked files to the index
• Ignore files locally
• Remove file from repo without removing local copy
• Find out a tracking branch
• Stop tracking a file
• Prepare a single-file patch and apply it
• Push an empty commit
• List all conflicted files
• Checkout only a subdirectory
• Trun a repo subdirectory into a separate repo

GPG

• Choose GPG key when signing
• Move keys between machines

JavaScript

• Maps are different from objects
• Map over map

Linux

• Check MX record for a domain

Make

• Keep going when a target fails or ignore specific errors of a recipe

PostgreSQL

• Add a column to a busy table
• Update with join
• Using grouping sets in postgresql
• Check if a key exists in a JSON or array
• How to cross join tables?
• Select data based on timestamps range
• grouping with aggregate filtering (group by ... having)
• Add non-null column to a large table
• Check if JSONB array contains element
• How to check table's indices?
• Run PostgreSQL in a docker container

RabbitMQ

• Execute an Erlang snippet on a node in container
• Wait for the node/app to start/stop
• Connect to a node via remote shell

Sed

• Use environment variable with replacement
• Replace lines in file

Shell

• find: Remove all files matching a pattern
• Test if a command or file exist
• Revert lines order
• See what processes are listening on TCP/UDP ports (OSX)
• Capture UDP data with nc
• Produce sequence of arbitrary strings
• Format a nice timestamp
• Increment a variable
• Iterate over pairs of items
• Print a range of commands from history
• Get the last match in a file and the following lines
• Remove string prefix and suffix
• Print lines from a file between patterns

SSL/TLS

• Generate chain of x590 v3 certificates

Vim

• Count The Number Of Matches