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For 2023 (and 2024 ...) - we are now fully retired from IT training.
We have made many, many friends over 25 years of teaching about Python, Tcl, Perl, PHP, Lua, Java, C and C++ - and MySQL, Linux and Solaris/SunOS too. Our training notes are now very much out of date, but due to upward compatability most of our examples remain operational and even relevant ad you are welcome to make us if them "as seen" and at your own risk.

Lisa and I (Graham) now live in what was our training centre in Melksham - happy to meet with former delegates here - but do check ahead before coming round. We are far from inactive - rather, enjoying the times that we are retired but still healthy enough in mind and body to be active!

I am also active in many other area and still look after a lot of web sites - you can find an index ((here))
Automating processes through Expect

What is Expect? Let me give you an example of how it's used to help answer that question.

I want to connect to a remote host that I can access through FTP, and have a look at all the files with "top", "sql" and "txt" in their names in my home directory. And that's something I need to do on a regular basis - perhaps checking logs on a web server.

I could type in the instructions longhand - but that would get monotonous on a regular basis - so I would prefer to run FTP controlling it like a puppet on a string - and that string in Expect.

Firstly, I do the job manually, once, and note down the exact prompts that I get, and the exact strings I type in. You noted, I hope, that I say "exact", didn't you - I must get spaces, carriage returns, line feeds right.

Then I write my code. The spawn command is used to trigger FTP. The expect command is used to await a prompt. And the send command is used to answer those prompts. Finally, I can use the variable called expect_out(buffer) which stores the complete response received prior to each "expect" to look at my results.

Here's a working example.

log_user 0
# Expect is a Tcl extension
# So all the Tcl commands are available too
puts "yes I am tickling"
spawn ftp
expect "): "
send "trainee\r"
expect "sword: "
send "abc123\r"
expect "ftp> "
send "ls\r"
expect "ftp> "
# The response we just got will have included
# the lines we want (and much more!) so that we
# can now use regular Tcl commands to extract it
set parts [split $expect_out(buffer) \n]
foreach line $parts {
  if {[regexp top|sql|txt $line]} {puts $line}
# Close out cleanly
send "quit\r"
expect "eof"

That's very much a "spike" solution - a demonstration of principles; the expect command can wait for a whole series of alternatives (including error conditions) and the application above could be extended to handle them as appropriate, for example. And you can even run multiple spawned processes in parallel.

As well as Tcl commands, you can use Tk commands with Expect - that means that you can put a graphic front end onto it. One of the things I need to do from time to time is to check whether my servers are up and running, and an Expect and Tk tool is ideal for the purpose. You can see my source code here.

Expect, and Tcl are covered on our Tcl and Expect course. We cover Tk on our Tk course

(written 2008-04-05)

Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
T211 - Tcl/Tk - What is Expect? Why use it?
  [286] Automating regular manual procedures - (2005-04-21)
  [435] Expect for Windows - (2005-09-04)
  [1173] Cheat Sheet / Check list for Expect maintainers - (2007-05-02)
  [1174] Installing Tcl and Expect on Solaris 10 - a checklist - (2007-05-02)
  [1409] What is Expect? - (2007-10-26)
  [1411] Buffering of inputs to expect, and match order - (2007-10-27)
  [1469] Curley brackets v double quotes - Tcl, Tk, Expect - (2007-12-12)
  [1531] Expecting a item from a list of possibles - (2008-02-04)
  [2474] Using Tcl and Expect to automate repetitive jobs - (2009-10-24)
  [2489] Parallel Pinging, using Python Threads or Expect spawn lists - (2009-11-02)
  [3009] Expect in Perl - a short explanation and a practical example - (2010-10-22)
  [3286] Should we cover expect and/or Tk on our public Tcl courses? - (2011-05-11)
  [3572] Adding Expect on top of Tcl - what is it and where can I get a training course to learn about it? - (2012-01-08)
  [4405] Backup procedures - via backup server - (2015-01-24)
  [4678] Expect with Ruby - a training example to get you started - (2016-05-18)

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Do not SHOUT and do not whisper
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Cambidge - Tcl, Expect and Perl courses
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This is a page archived from The Horse's Mouth at http://www.wellho.net/horse/ - the diary and writings of Graham Ellis. Every attempt was made to provide current information at the time the page was written, but things do move forward in our business - new software releases, price changes, new techniques. Please check back via our main site for current courses, prices, versions, etc - any mention of a price in "The Horse's Mouth" cannot be taken as an offer to supply at that price.

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