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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.

Example: wargames

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 Ashier refuse wargames automatically.

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 ENTER.

>Would you like to play a game?
!terminal "no"

Then, enter the following command to run Ashier, which starts a new interactive shell. The -c option points Ashier to the configuration file you just created.

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.

Example: ping

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.

This 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 others. Second, wargames takes only a fixed no response, but here Ashier needs to react differently to ping responses: do nothing for the first 9, and press 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 SPACE 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 dots.

>64 bytes from ( 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 (shown 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 Ctrl-C key 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.


import sys

print '/bin/ping %s' % sys.argv[1]  # Run ping from the interactive shell

with open(sys.argv[2], '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 and its arguments.

ashier -c ping-output.ahr ./ 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 ping with Ctrl-C and types exit to quit the new interactive shell.


Automating Terminal Interactions with Templates



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