web scraping to fill out (and retrieve) search forms?

Beautiful Soup is great for parsing webpages- that's half of what you want to do. Python, Perl, and Ruby all have a version of Mechanize, and that's the other half:

http://wwwsearch.sourceforge.net/mechanize/

Mechanize let's you control a browser:

# Follow a link
browser.follow_link(link_node)

# Submit a form
browser.select_form(name="search")
browser["authors"] = ["author #1", "author #2"]
browser["volume"] = "any"
search_response = br.submit()

With Mechanize and Beautiful Soup you have a great start. One extra tool I'd consider is Firebug, as used in this quick ruby scraping guide:

http://www.igvita.com/2007/02/04/ruby-screen-scraper-in-60-seconds/

Firebug can speed your construction of xpaths for parsing documents, saving you some serious time.

Good luck!

Python Code: for search forms.

# import 
from selenium import webdriver

from selenium.common.exceptions import TimeoutException

from selenium.webdriver.support.ui import WebDriverWait # available since 2.4.0

from selenium.webdriver.support import expected_conditions as EC # available since 2.26.0

# Create a new instance of the Firefox driver
driver = webdriver.Firefox()

# go to the google home page
driver.get("http://www.google.com")

# the page is ajaxy so the title is originally this:
print driver.title

# find the element that's name attribute is q (the google search box)
inputElement = driver.find_element_by_name("q")

# type in the search
inputElement.send_keys("cheese!")

# submit the form (although google automatically searches now without submitting)
inputElement.submit()

try:
    # we have to wait for the page to refresh, the last thing that seems to be updated is the title
    WebDriverWait(driver, 10).until(EC.title_contains("cheese!"))

    # You should see "cheese! - Google Search"
    print driver.title

finally:
    driver.quit()

Source: https://www.seleniumhq.org/docs/03_webdriver.jsp