Expect: automation and semi-automation of processes under Linux
Friday August 7th 2020 by SocraticDev
Expect is a
TCL based utility which excels in automating interactive tasks.
Expectis a program that "talks" to other interactive programs according to a script. Following the script, Expect knows what can be expected from a program and what the correct response should be. An interpreted language provides branching and high-level control structures to direct the dialogue. In addition, the user can take control and interact directly when desired, afterward returning control to the script.
-- man page for
This short script below (** strongly discouraged **) automatically provides your root password when requested by the system. This example illustrates the interactive aspect of automation with
Expect. The script starts, performs certain actions, and returns control to the user.
expect -c ' spawn bash sleep 0.3 send -- "sudo ls\n" expect "password for" send -- "<Your Password>\n" interact exit '
Some use cases
Expectwas used, in the time of telephone modem connections, for the server to call users and, thus, avoid charges for the call;
- Reliability and sustainability: it is used as an automated testing tool by critical components of
LLVM. It is therefore worth the cost of investing time and effort to learn how to use it well and integrate it into your workflow;
- Executing tasks usually performed by humans as they involve periods of inactivity, cursor movement, etc;
- Automatically triggering completion with
TABand then hand over to the user;
- Automatically invoking keyboard shortcuts in
- Interacting naturally with programs like a human would;
- Filling in the gaps of a program where it would lack ways to interact programmatically with it, but on the other hand allowing a human user to do it manually;
- Partial automation: performing certain operations and then handing over to a human user.
Expect better known?
- It is a very ecclectic application. First of all, its name,
Expect, is really not great in terms of
SEO. Rather difficult to look for help in
- Then, it's an interpreter who doesn't really have his own language.
TCLwhile adding extensions to it. Thus, it is sometimes difficult to determine if we are dealing with vanilla
TCLor a peculiarity of
- Despite its weak presence on the web, by reading the documentation related to
TCL, we discover a universe of unsuspected possibilities to benifit from your