Append line to /etc/hosts file with shell script

Question

I have a new Ubuntu 12.04 VPS. I am trying to write a setup script that completes an entire LAMP installation. Where I am having trouble is appending a line to the /etc/hosts file. My current hosts file looks like this:

127.0.0.1       localhost Venus

# The following lines are desirable for IPv6 capable hosts
::1     ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters

I would like it to look like this:

127.0.0.1       localhost Venus
192.241.xx.xx  venus.example.com venus

# The following lines are desirable for IPv6 capable hosts
::1     ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters

I have tried a variety of sed commands using the append (\a) command. For some reason Ubuntu either just echoes the contents of the hosts file in terminal or does nothing at all. How would I properly inject the second line into the file with a bash script?

Solution 1

Make sure to use the -i option of sed.

-i[SUFFIX], --in-place[=SUFFIX]
  edit files in place (makes backup if extension supplied)

sed -i "2i192.241.xx.xx  venus.example.com venus" /etc/hosts

Otherwise,

echo "192.241.xx.xx  venus.example.com venus" >> /etc/hosts

would append the line at the end of the file, which could work as you expect.

Solution 2

Insert/Update Entry

If you want to programmatically insert/update a hosts entry using bash, here's a script I wrote to do that:

#!/bin/bash

# insert/update hosts entry
ip_address="192.168.x.x"
host_name="my.hostname.example.com"
# find existing instances in the host file and save the line numbers
matches_in_hosts="$(grep -n $host_name /etc/hosts | cut -f1 -d:)"
host_entry="${ip_address} ${host_name}"

echo "Please enter your password if requested."

if [ ! -z "$matches_in_hosts" ]
then
    echo "Updating existing hosts entry."
    # iterate over the line numbers on which matches were found
    while read -r line_number; do
        # replace the text of each line with the desired host entry
        sudo sed -i '' "${line_number}s/.*/${host_entry} /" /etc/hosts
    done <<< "$matches_in_hosts"
else
    echo "Adding new hosts entry."
    echo "$host_entry" | sudo tee -a /etc/hosts > /dev/null
fi

The script is intended for use with OS X but would work on linux as well with minor tweaking.

Solution 3

If your in mac or you need sudo permission to this try this:

sudo -- sh -c -e "echo '192.34.0.03   subdomain.domain.com' >> /etc/hosts";

It will still ask you for password.

alternative way from @kainjow

echo '192.34.0.03 subdomain.domain.com' | sudo tee -a /etc/hosts

Solution 4

echo "127.0.0.1 localhost `hostname`">./temp_hosts
echo "192.241.xx.xx  venus.example.com">>./temp_hosts
cat /etc/hosts |tail -n +2 >>./temp_hosts
cat ./temp_hosts > /etc/hosts
rm ./temp_file

Solution 5

I should point out that sed (the stream editor) is not actually intended for editing files, although it can be used to do that. (Standard sed doesn't have a built-in mechanism for writing to other than standard output.) A more appropriate tool would be ed.

The following ed script says "find the line containing the (admittedly sloppy) regular expression /127.0.0.1/ and append at the next line." (The lone period tells ed to stop appending.)

ed /etc/hosts <<-'EOF'
    /127.0.0.1/a
    192.241.xx.xx  venus.example.com
    .
    wq
EOF

That said, you can really just append this line to the end of your /etc/hosts file very trivially:

echo '192.241.xx.xx  venus.example.com' >> /etc/hosts

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