hostsfile
This library, and the associated command line binary, will help you manipulate your /etc/hosts file. Both the library and the binary will leave comments and other metadata in the /etc/hosts file as is, appending or removing only the lines that you want changed. A description of the API can be found at godoc.
Installation
On Mac, install via Homebrew:
brew install kevinburke/safe/hostsfile
If you have a Go development environment, you can install via source code:
go get github.com/kevinburke/hostsfile@latest
Command Line Usage
Easily add and remove entries from /etc/hosts.
# Assign 127.0.0.1 to all of the given hostnames
hostsfile add www.facebook.com www.twitter.com www.adroll.com 127.0.0.1
# Remove all hostnames from /etc/hosts
hostsfile remove www.facebook.com www.twitter.com www.adroll.com
You may need to run the above commands as root to write to /etc/hosts (which
is modified atomically).
To print the new file to stdout, instead of writing it:
hostsfile add --dry-run www.facebook.com www.twitter.com www.adroll.com 127.0.0.1
You can also pipe a hostsfile in:
cat /etc/hosts | hostsfile add --dry-run www.facebook.com www.twitter.com www.adroll.com 127.0.0.1
Or specify a file to read from at the command line:
hostsfile add --file=sample-hostsfile www.facebook.com www.twitter.com www.adroll.com 127.0.0.1
Library Usage
You can also call the functions in this library from Go code. Here's an example where a hosts file is read, modified, and atomically written back to disk.
package main
import (
"bytes"
"fmt"
"log"
"net"
"os"
hostsfile "github.com/kevinburke/hostsfile/lib"
)
func checkError(err error) {
if err != nil {
log.Fatal(err.Error())
}
}
func main() {
f, err := os.Open("/etc/hosts")
checkError(err)
h, err := hostsfile.Decode(f)
checkError(err)
local, err := net.ResolveIPAddr("ip", "127.0.0.1")
checkError(err)
// Necessary for sites like facebook & gmail that resolve ipv6 addresses,
// if your network supports ipv6
ip6, err := net.ResolveIPAddr("ip", "::1")
checkError(err)
h.Set(*local, "www.facebook.com")
h.Set(*ip6, "www.facebook.com")
h.Set(*local, "news.ycombinator.com")
h.Set(*ip6, "news.ycombinator.com")
// Write to a temporary file and then atomically copy it into place.
tmpf, err := os.CreateTemp("/tmp", "hostsfile-temp")
checkError(err)
err = hostsfile.Encode(tmpf, h)
checkError(err)
err = os.Chmod(tmp.Name(), 0644)
checkError(err)
err = os.Rename(tmp.Name(), "/etc/hosts")
checkError(err)
fmt.Println("done")
}