Show HN: Xo, a sed-like command line utility that composes regex matches

I typically fall back to perl when sed isn't quite versatile/cross-platform enough. What do Go regular expressions offer over Perl regular expressions? (Performance, I imagine.)

Obviously it is not line-oriented. So the selling points are? 1. custom delimiters 2. special syntax for fallback values 3. extended regular expression with Unicode support

More?

Some fun examples of what you can do with `xo`,

Hello world:

    echo 'Hello! My name is C3PO, human cyborg relations.' | xo '/^(\w+)! my name is (\w+)/$1, $2!/i'
    # => Hello, C3PO!

A quick breakdown on the syntax:

    echo 'Hello! My name is C3PO.' | xo '/^(\w+)?! my name is (\w+)/$1, $2!/i'
    ^                              ^     ^^                       ^ ^     ^ ^
    |______________________________|     ||_______________________| |_____| |
                    |                    + Delimiter |                 |    + Flag
                    + Piped output                   + Pattern         + Formatter

Boot up a Rails server with Stripe keys:

    # ./secrets/stripe.yml
    secret_key: fE3J2Z76ry
    publishable_key qYB7936Qos

Then read it and boot Rails with keys set as env vars, (without logging to the console!)

    cat secrets/stripe.yml | xo '/secret_key:\s([\w]+).*?publishable_key:\s([\w]+)/PUBLISHABLE_KEY=$1 SECRET_KEY=$2 rails s/mis' | sh
    # => PUBLISHABLE_KEY=fE3J2Z76ry SECRET_KEY=qYB7936Qos rails s

View modified files in the last commit:

    git --no-pager log -n 1 | xo '/^commit\s([^\n]+)/git diff-tree --no-commit-id --name-status -r $1/' | sh
    # =>
    # M     some-modified-file.txt
    # A     some-added-file.txt

Nice to put this in a script called `git-last-modified` inside of `/usr/local/bin`, then use `git last-modified`.

Decode a hidden message:

    # ./hidden-message.txt
    WITHIN THIS MULTILINE the STRING
    LIES A HIDDEN MESSAGE meaning of
    life  THAT COULD  BE is HARD  TO
    READ 42
    
    8)

Then read it with,

    cat hidden-message.text | xo '/([a-z0-9\)]+)/$1/' | xargs
    # => the meaning of life is 42 8)

Read a config file containing SSH info:

    # ./servers.yml
    stages:
      production:
        server: 192.168.1.1:1234
        user: user-1
      staging:
        server: 192.168.1.1
        user: user-2

Then read it with,

    ssh $(cat servers.yml | xo '/.*?(production):\s*server:\s+([^:\n]+):?(\d+)?.*?user:\s+([^\n]+).*/$4@$2 -p $3?:22/mis')
    # => ssh user-1@192.168.1.1 -p 1234
    

What if we didn't specify a port, i.e. like staging? Fallback values! (Notice the ternary operator, `?:`)

    ssh $(cat servers.yml | xo '/.*?(staging):\s*server:\s+([^:\n]+):?(\d+)?.*?user:\s+([^\n]+).*/$4@$2 -p $3?:22/mis')
    # => ssh user-2@192.168.1.1 -p 22

Now turn that into a `~/.bashrc` function and we're golden,

    function shh() {
      ssh $(cat servers.yml | xo "/.*?($1):\s*server:\s+([^:\n]+):?(\d+)?.*?user:\s+([^\n]+).*/\$4@\$2 -p \$3?:22/mis")
    }
    

And then we can use it like,

    shh production
    # => ssh user-1@192.168.1.1 -p 1234