When using expect script on boot the output of a list of lines gets shorted. How to increase expect's or the terminal's buffer on boot?

Question

I use the following script that I generated with autoexpect. When used on command line command sudo surfshark-vpn multi gives a list of about 15 lines and then asks for a final input by the user in the form of a number.

However, when using the expect script on boot those 15 lines become one line each with asking for Enter after each line.

I wonder why this happens. Somehow the command seems to think the shell has just one line.

 $ cat startsurfshark.sh
#!/usr/bin/expect -f
#
# This Expect script was generated by autoexpect on Sat Dec 12 15:36:12 2020

set force_conservative 0  ;# set to 1 to force conservative mode even if
              ;# script wasn't run conservatively originally
if {$force_conservative} {
    set send_slow {1 .1}
    proc send {ignore arg} {
        sleep .1
        exp_send -s -- $arg
    }
}

set timeout -1
log_file /home/USER/startshark.log
spawn $env(SHELL)
match_max 100000
send -- "sudo surfshark-vpn multi\r"
expect -exact "\[sudo\] Passwort for USER: "
send -- "PASSWORD"

expect -exact "press enter for next page"
send -- "\r"

expect -exact "press enter for next page"
send -- "\r"

expect -exact "press enter for next page"
send -- "\r"

expect -exact "press enter for next page"
send -- "\r"

# ... in here should be a lot more 

# ... it then should continou like this

expect -exact "Enter a number to select the location\r"
send -- "2\r"

expect -exact "\r
Enter a number to select the VPN connection type. For default UDP, press ENTER\r
0 TCP\r
1 UDP\r
1 selected\r
"
send -- "\r"
expect -exact "\r
Checking for connection status...\r"
sleep 15
send -- "exit"

Note that I added several lines in the following form manually. That's how I found out about the weird behaviour:

expect -exact "press enter for next page"
send -- "\r"

Note also, that this script would work fine with attack instead of multi because the other command will not print a list that tries to stay on the monitor for the user to watch even if it is too large for the monitor size.

The output of my logfile is:

 $ cat ../startshark.log 
spawn /bin/bash
sudo surfshark-vpn multi
~ - 21:19:10 - ben - [email protected] Mo Dez 14 
 $ sudo surfshark-vpn multi
[sudo] Passwort für ben: 

press enter for next page
0 France Paris
press enter for next page
1 Germany Frankfurt am Main
press enter for next page
2 Hong Kong Hong Kong
press enter for next page
3 India Chennai

When running the script from a terminal manually (not on boot) it will display the list as follows:

0 France Paris
1 Germany Frankfurt am Main
2 Hong Kong Hong Kong
3 India Chennai
4 Netherlands Amsterdam
5 Netherlands Amsterdam
6 Portugal Loule
7 Singapore Singapore
8 Sweden Stockholm
9 United Kingdom Manchester
10 United Kingdom London
11 United States San Francisco
12 United States Dallas
13 United States New York
Enter a number to select the location

I could also use a form of a while loop to press enter until the list ends. How would I do that?

meuh · Accepted Answer · 2020-12-15 15:28:54Z

When you do spawn ... in expect, it creates a pty terminal that inherits the setting of the current tty the program is running in.

So, when testing the script in a terminal with, for example, 24 rows (lines), the vpn program will see this and interact appropriately, prompting for input every 24 lines of output.

If you now run your script from a systemd unit, for example, there is no tty to inherit settings from, and the number of rows and columns default to 0. The vpn program therefore behaves differently.

The solution is to explicitly set the desired number of rows and columns before doing the spawn. In expect this is done by setting a variable before the spawn ... line:

set stty_init "rows 24 cols 80"

You might even ben able to set rows 999 and avoid all page prompts.

glenn jackman · Accepted Answer · 2020-12-14 21:23:41Z

1

I don't understand about the boot/non-boot differences.

However, this is how to loop over that "press enter" business:

expect {
    -exact "press enter for next page" {
        send -- "\r"
        exp_continue
    }
    -exact "Enter a number to select the location\r"
}
send -- "2\r"

answered Dec 14, 2020 at 21:23

glenn jackman

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