Don Libes' Expect: A Surprisingly Underappreciated Unix Automation Tool

Post by ChuckMcM » Thu, Dec 08, 2016, 10:09 PM UTC

kazinator wrote: post #67

ChuckMcM wrote: post #49

This tool keeps the command line interpreter (CLI) alive. Sysadmins everywhere can glue hundred different systems from a hundred different vendors together if they have CLI and the sysadmin has access to a machine that runs expect(1). There are many stories of complex infrastructure being taken down by new firmware on routers or switches that change the order of parameters in a command :-)

Rather, this tool keeps alive systems that do not have easily scriptable command interfaces, and must be driven at the character-level through their interactive visual interfaces. If the system has a CLI, you write a script in that CLI; you don't write an expect script. Sometimes systems have CLI, but only behind a remote access wall (telnet, serial, ...); then you might use expect---because there is no way to upload…

   > Sometimes systems have CLI, but only behind a 
   > remote access wall (telnet, serial, ...); then 
   > you might use expect-

Post by EvilTerran » Thu, Dec 08, 2016, 10:30 PM UTC

ianmcgowan wrote: post #34

geff82 wrote: post #28

I used expect heavily at several clients in the past and have never seen someone else use it. I never used it as a precise tool, rather as a Sledgehammer. I think I remember I used Expect to script remote machines (expect was literally the "programmer") when everything else failed and was "prevented" due to policy. I guess my script was also non-compliant, but noone complained.

I've done the same thing, and on the windows side of things AutoIT ( https://www.autoitscript.com/ ) is similarly flexible when all else fails. It's not pretty, but arguably is a good example of the hacker ethic.

Post by daenz » Thu, Dec 08, 2016, 10:57 PM UTC

spangry wrote: post #54

daenz wrote: post #47

Shameless self promotion: if you want to automate subprocesses with python in an intuitive way, give sh a try: https://github.com/amoffat/sh

Man, I was so happy when I discovered your library. It's how I always felt subprocess should be. With split('\n') and basic string parsing there's little that can't be automated with sh. Keep up the good work!

Post by [deleted] » Thu, Dec 08, 2016, 11:07 PM UTC

robertelder wrote: post #24

skywhopper wrote: post #19

Expect is a last ditch tool that becomes less and less necessary as automation libraries and remote APIs become more and more common. The examples given are cute but hardly representative of what expect is really for. The only times I've needed to use expect was to drive weird non-scriptable telnet-based remote systems and to automate unpackaging of intentionally-broken vendor-supplied self-expanding software archive…

Do you have any links to examples of what it is really for? I've had a hard time finding code examples because the reasons listed at the bottom of the article.

Post by schoen » Thu, Dec 08, 2016, 11:18 PM UTC

stcredzero wrote: post #51

seiferteric wrote: post #2

Expect is cool, I have used it in the past as well as the expect perl module, but in my opinion is always a suboptimal way to automate things. It's always better and more robust to have a proper interface to script things instead of relying on matching brittle text/regex responses and timers and such. Of course sometimes it's not possible, so expect comes in handy.

Expect is cool, I have used it in the past as well as the expect perl module, but in my opinion is always a suboptimal way to automate things. When I was a graduate Comp Sci TA in the 1990's, it was the perfect way to automate grading the Unix shell that the Systems Software class was supposed to write. Effectively, I was also writing a regression/functional testing system for the class. I explained that the Expect/T…