Go parser for SSH config files
GitHub - kevinburke/ssh_config: Go parser for ssh_config files
ssh_config
This is a Go parser for ssh_config files. Importantly, this parser attempts
to preserve comments in a given file, so you can manipulate a ssh_config file
from a program, if your heart desires.
It's designed to be used with the excellent
x/crypto/ssh package, which handles SSH
negotiation but isn't very easy to configure.
The ssh_config Get() and GetStrict() functions will attempt to read values
from $HOME/.ssh/config and fall back to /etc/ssh/ssh_config. The first
argument is the host name to match on, and the second argument is the key you
want to retrieve.
port := ssh_config.Get("myhost", "Port")
Certain directives can occur multiple times for a host (such as IdentityFile),
so you should use the GetAll or GetAllStrict directive to retrieve those
instead.
files := ssh_config.GetAll("myhost", "IdentityFile")
You can also load a config file and read values from it.
var config = `
Host *.test
  Compression yes
`

cfg, err := ssh_config.Decode(strings.NewReader(config))
fmt.Println(cfg.Get("example.test", "Port"))
Some SSH arguments have default values - for example, the default value for
KeyboardAuthentication is "yes". If you call Get(), and no value for the
given Host/keyword pair exists in the config, we'll return a default for the
keyword if one exists.
Manipulating SSH config files
Here's how you can manipulate an SSH config file, and then write it back to
disk.
f, _ := os.Open(filepath.Join(os.Getenv("HOME"), ".ssh", "config"))
cfg, _ := ssh_config.Decode(f)
for _, host := range cfg.Hosts {
    fmt.Println("patterns:", host.Patterns)
    for _, node := range host.Nodes {
        // Manipulate the nodes as you see fit, or use a type switch to
        // distinguish between Empty, KV, and Include nodes.
        fmt.Println(node.String())
    }
}

// Print the config to stdout:
fmt.Println(cfg.String())
Spec compliance
Wherever possible we try to implement the specification as documented in
the ssh_config manpage. Unimplemented features should be present in the
issues list.
Notably, the Match directive is currently unsupported.
Errata
This is the second comment-preserving configuration parser I've written, after
an /etc/hosts parser. Eventually, I will write one for every Linux
file format.
Sponsorships
Thank you very much to Tailscale and Indeed for sponsoring development of this
library. Sponsors will get their names featured in the README.
You can also reach out about a consulting engagement: https://burke.services
