01.26
When I have to migrate servers to new OS or reinstall list of gems on another box you can get a quite big list of gems to install. This post will describe how to do it “admin way” which basically means that whatever has to be done more than once should be scripted 
To get a list of all installed gems you can use this command:
*** LOCAL GEMS ***
actionmailer (2.3.2, 2.1.0, 2.0.2, 1.3.3)
actionpack (2.3.2, 2.1.0, 2.0.2, 1.13.6, 1.13.3)
actionwebservice (1.2.6, 1.2.3)
activerecord (2.3.2, 2.1.0, 2.0.2, 1.15.6, 1.15.3)
activeresource (2.3.2, 2.1.0, 2.0.2)
activesupport (2.3.2, 2.1.0, 2.0.2, 1.4.4, 1.4.2)
archive-tar-minitar (0.5.2)
builder (2.1.2)
camping (1.5)
capistrano (2.5.5, 1.4.1)
cgi_multipart_eof_fix (2.5.0, 2.1)
chronic (0.2.3)
color (1.4.0)
columnize (0.3.0)
daemons (1.0.10, 1.0.6)
dcov (0.2.2)
fastthread (1.0.7, 1.0)
GData (0.0.4)
gem_plugin (0.2.3, 0.2.2)
googlecalendar (1.1.0)
highline (1.5.1)
hoe (1.12.2, 1.8.3)
hpricot (0.8.1, 0.6)
httpclient (2.1.5.2)
json (1.2.0, 1.1.6)
json_pure (1.2.0)
kwala (0.9.1)
linecache (0.43)
log4r (1.0.5)
markaby (0.5)
memcache-client (1.7.6)
metaid (1.0)
mocha (0.9.8, 0.9.5, 0.5.5)
mongrel (1.1.5, 1.0.1)
mongrel_cluster (1.0.5, 0.2.1)
needle (1.3.0)
net-scp (1.0.2)
net-sftp (2.0.2, 1.1.0)
net-ssh (2.0.11, 1.1.1)
net-ssh-gateway (1.0.1)
packet (0.1.15)
parseexcel (0.5.2)
passenger (2.2.5)
pdf-writer (1.1.8)
rack (1.0.0)
rails (2.3.2, 2.1.0, 2.0.2, 1.2.3)
rake (0.8.7, 0.8.6, 0.8.4, 0.8.3, 0.8.1, 0.7.3)
redgreen (1.2.2)
rfacebook (0.9.8, 0.9.7)
rmagick (2.12.2, 1.15.7)
roo (1.2.3)
ruby-debug (0.10.3)
ruby-debug-base (0.10.3)
ruby-hmac (0.3.2)
ruby-ole (1.2.8.2)
ruby-openid (2.1.6, 2.0.4)
rubyforge (2.0.3, 1.0.3, 1.0.2)
rubyzip (0.9.1)
select_with_include (0.0.1)
simple-rss (1.2, 1.1)
sources (0.0.1)
spreadsheet (0.6.3.1)
system_timer (1.0)
termios (0.9.4)
test-spec (0.10.0)
tmail (1.2.3.1)
transaction-simple (1.4.0)
will_paginate (2.2.2)
xml-simple (1.0.12, 1.0.11)
Imagine that you have to install those gems one by one…. grrrrrrrrrrrr :[
Here is a small Perl script that will create commands for you which you can use to install all of listed gems at another server:
# We're strict
use strict;
# Get list of installed gems
my @gems = qx(gem list);
chomp(@gems);
# Create commands
foreach my $gem (@gems)
{
# Match gem and versions
$gem =~ m/(\S+)\s\((.+)\)/i;
# Gem name
$gem = $1;
# Save them into array
my @gem_versions = split(/,/, $2);
# Print out commands
foreach (@gem_versions)
{
# Remove all whitespaces
$_ =~ s/^\s+//;
print "gem install $gem --version=$_\n";
}
}
Now when you run it you will se something like this:
gem install actionmailer --version=2.3.2
gem install actionmailer --version=2.1.0
gem install actionmailer --version=2.0.2
gem install actionmailer --version=1.3.3
gem install actionpack --version=2.3.2
gem install actionpack --version=2.1.0
gem install actionpack --version=2.0.2
...
gem install xml-simple --version=1.0.12
gem install xml-simple --version=1.0.11
That’s a lot of gems (I’ve cut the output to shorten scrolling) ! Thanks God I wrote that script
Let’s reinstall these gems:
Now paste what you did get form the script or print (pipe) to file and run it via sh on another box:
Successfully installed activesupport-2.3.2
Successfully installed actionpack-2.3.2
...
And when this is cooking, we can handle the real stuff, someone just send a ticket about new vhost in Apache, boy this is so much more interesting than installing gems
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