List of interesting commands

SSH Keys

• rsa keys with openssl

  # Write the public part of a RSA key in OpenSSH format (basically
  # just prefix it with 'ssh-rsa' and collapse everything. Also remove
  # the ASCII guards.
  openssl pkey -in file.pem -pubout | sed -ne :a -e '1d;$!{H;n;ba;}' \
    -e 'x;s/\n//g;s/^/ssh-rsa /p'
  
  # Generate a RSA private SSH key, using OpenSSL's genpkey command
  # (4096 bits)
  openssl genpkey -out file.pem -outform PEM -algorithm rsa \
    -pkeyopt rsa_keygen_bits:4096
  

Bash

• group files by extension with associative arrays

  # Read a list of files with sizes and group them by extension, adding
  # the size.
    
  declare -A files=();
  while read -r size filename; do
    basename=${filename##*/}; ((files["${basename##*.}"]+=size));
  done <<<  $'10 foo/bar/baz.ext\n20 foo/bar/bleh.ext\n40 music/some/song.mp3'
  declare -p files
    
  Output:
  > declare -A files='([mp3]="40" [ext]="30" )'
  

Git

• branches

  # Delete a branch in a remote
  git push <remote> :branch_name
  
  # Update a remote, considering also deleted branches
  git remote update -p # -p comes from 'prune'