Ashier for Automating Terminal Interactions
Ashier is a program that serves the same purpose as expect: helping users script terminal interactions. It is a computer assistant that watches the terminal screen over your shoulder and interacts with the terminal using its own keyboard; someone to answer the boring questions and enter the tedious commands for you. Unlike expect, Ashier supports multiple programming languages and provides a readable template language for terminal output matching. These features make it easier to create and to maintain scripted terminal interactions.
Ashier is not an official Google product.
wargames is a program that asks you to play a game and then tells you that
the only winning move is not to play. This example shows how you can make
First, create a file
wargames.ahr with the following contents. The first
line, which starts with
>, is a template that tells Ashier what to look for
on the terminal. Here, it tells Ashier to look for a line that starts with the
sentence "Would you like to play a game?". The second line, which starts with
!terminal, tells Ashier how to react when it matches terminal output to the
template. Here, it tells Ashier to type
no into the terminal and press
>Would you like to play a game? !terminal "no"
Then, enter the following command to run Ashier, which starts a new interactive
-c option points Ashier to the configuration file you just
ashier -c wargames.ahr
When you run
/usr/games/wargames in this shell, Ashier automatically answers
"no" to the "Would you like to play a game?" prompt.
To stop Ashier, type
exit in the interactive shell.
ping is a program that sends network packets to a remote host and reports the
responses. It has a command line option to send a specific number of packets,
but no option to continue sending packets until it receives, say, 10 responses.
This example shows how you can implement that feature with Ashier.
ping example differs from the
wargames example in two ways. First,
wargames has a fixed prompt, but
ping responses vary in reported packet
size, source, sequence number, Time-to-Live value, and latency. So Ashier
needs to match only some parts of the template and ignore differences in
wargames takes only a fixed
no response, but here Ashier
needs to react differently to
ping responses: do nothing for the first 9, and
Ctrl-C for the 10th. In other words, Ashier needs to support dynamic
behavior through custom stateful logic.
Ashier solves the first problem with variable markers, which appear on lines
2-6 in the
ping-output.ahr configuration file (shown below). Each variable
marker line starts with
?, followed by an optional sequence of
characters, and then a sequence of
. dots. The dots on each variable marker
line marks the corresponding part of the template as a variable, which tells
Ashier to ignore differences there when matching terminal output with the
template. Each variable marker can also have a name, which appears after the
>64 bytes from slashdot.org (188.8.131.52): icmp_seq=3 ttl=230 time=94.4 ms ?.. ? ............................ ? . seq ? ... ttl ? .... time !controller "REPLY $seq $ttl $time"
Ashier solves the second problem with a controller process. When Ashier starts, it in turn starts another program in the background. That running program is the controller process, which implements dynamic behavior for Ashier. Ashier talks to the controller process by sending messages to its standard input. In return, the controller process may send data to standard output, which Ashier forwards verbatim to the terminal as keystrokes.
Here, the last line of
ping-output.ahr (above) tells Ashier to send a message
to the controller process (instead of typing into the terminal) when it matches
terminal output to the template. The controller program
below) reads these messages and dynamically generates keystrokes. Since Ashier
starts with a new interactive shell, the controller process first enters a
shell command to run the
ping program. Then, it reads 10 Ashier messages
(each representing a
ping response) from standard input and logs each message
to the output file. After receiving all 10 messages, it sends the
combination to standard output, which terminates
ping and drops the terminal
back to the interactive shell. Finally, it enters the
exit command to quit
the interactive shell and stop Ashier.
#!/usr/bin/python import sys print '/bin/ping %s' % sys.argv # Run ping from the interactive shell with open(sys.argv, 'w') as output: # Open output file for writing responses = 0 while responses < 10: # Loop until 10 responses line = sys.stdin.readline() # Read Ashier controller message if line.startswith('REPLY '): # Check message label output.write(line[6:]) # Write response statistics to file responses += 1 # Increment response count sys.stdout.write(chr(3)) # Terminate ping with Ctrl-C print 'exit' # Quit the interactive shell
You can now enter the following command to run Ashier, which starts a new
interactive shell. The
-c option points Ashier to its configuration file,
and the remaining arguments specify the controller program
ashier -c ping-output.ahr ./ping-react.py google.com output.txt
In the new shell, Ashier automatically runs
ping and writes the statistics of
each response to
output.txt. When it counts 10 responses, it terminates
Ctrl-C and types
exit to quit the new interactive shell.