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Is it possible to make a bash shell script interact with another command line program?
(6 answers)
Closed 1 year ago.
I have a program JLinkExe which opens it's own prompt uponn execution. So I normally run it like this:
JLinkExe
and then type the commands at it's prompt that appears:
J-Link>
There are many applications with it's own prompt and I am interested in a general method that would enable me to send commands to any kind of application that has it's own prompt.
I already tried two methods. They both try to send commands in this order:
connect
Enter
Enter
Enter
Enter
erase
loadbin program.bin , 0x0
r
q
but both fail. Here is the first method:
{ echo 'connect';
echo '';
echo '';
echo '';
echo '';
echo 'erase';
echo 'loadbin program.bin , 0x0';
echo 'r';
echo 'q'; } | JLinkExe
And the second method (source):
JLinkExe <<EOF
connect
erase
loadbin program.bin , 0x0
r
q
EOF
I found these method on the internet but I don't understand why they fail. Especially the first one that worked in the past...
Can anyone propose any better / working / universally applicable method?
I think it might be because here-docs do not wait for output. Unfortunately for you I switched company, thus can't test my code below.
#! /bin/bash
expect <<-EOF
set timeout -1
spawn JLinkExe
expect "J-Link> " { send "connect\r" }
expect "J-Link> " { send "\r" }
expect "J-Link> " { send "\r" }
expect "J-Link> " { send "\r" }
expect "J-Link> " { send "\r" }
expect "J-Link> " { send "erase\r" }
expect "J-Link> " { send "loadbin program.bin , 0x0\r" }
expect "J-Link> " { send "r\r" }
expect "J-Link> " { send "q\r" }
expect eof
catch wait result
exit [lindex \$result 3]
EOF
exit $?
Except waits until J-Link> turns up and then sends the command through the connection.
If it doesn't work please notify me. I'll try to help you after the weekend :-)
EDIT:
A: Why did you wrap everything in expect 2>&1 <<-EOF and EOF?
You can add expect in the shebang, but I often use it as part of my Bash scripts. My knowledge of Bash is better.
B: Why a -EOF instead of EOF?
That's because <<-EOF allows leading tabs when you want to end the here-doc. You can indent it in functions for instance.
C: Why did you redirect stderr to stdout (2>&1)?
In your case I should've removed this. I took the code from one of my other answer about expect and tailored it to your needs.
D: What does catch wait result and exit [lindex \$result 3] do after we catch the eof?
Nice question, I had to look this one up a little myself:
lindex takes 4rd argument in \$result and exits the here-doc (0 is arg 1).
\$result is set by catch wait result.
Catch takes the output of wait and puts that into result.
Wait returns four integers:
First: pid of process that's being waited on.
Second: spawn ID.
Third: -1 for errors, 0 otherwise.
Forth: Exit status of the program as set by the OS.
Sources:
https://linux.die.net/man/1/expect
https://www.tcl.tk/man/tcl/TclCmd/catch.html
https://www.tcl.tk/man/tcl/TclCmd/lindex.html
Note that you have to escape the $ in the here-doc, otherwise Bash tries to process it. Hence \$result.
E: Why you exit with exit $?
Bash exits a script with the last known error code. Although you can leave it implicitly, I like to add it anyhow. It keeps the script more readable for beginners.
Related
I'm trying to write a shell function that spawns a ssh process and authentificates with a password. Then, I'd like to use the spawned process to do further stuff with expect.
Here's the function I have so far:
ssh_cmd() {
ssh $USER#$HOST 2>&1 | expect -c "
log_user 0
set timeout 5
expect password: {
send \"$PASS\n\"
sleep 2
log_user 1
}
"
}
And then I'd like to use given function in other places to interact with the ssh process like this:
ssh_cmd | expect -c "
expect '#' {
send pwd\n
send exit\n
}
expect eof
"
However, running the ssh_cmd function with -d option for expect I get the following result:
expect version 5.45.4
expect: does "" (spawn_id exp0) match glob pattern "password:"? no
ubnt#ui1's password: expect: timed out
From what I understand, the output of ssh does not get piped correctly. I know the common way to do this would be to use spawn, but that would mean the process would get killed after expect exits and I could not have a generic function that authentificates ssh sessions and keeps the process alive for further usage.
What you're designing won't work. Expect needs the process to be spawned from within the expect interpreter using the spawn command. Passing the command's stdout into expect is insufficient.
You could try this:
ssh_cmd() {
# a default bit of code if user does not provide one.
# you probably want some checking and emit an error message.
local user_code=${1:-set timeout 1; send "exit\r"; expect eof}
expect -c "
log_user 0
set timeout 5
spawn ssh -l $USER $HOST
expect password: {
send \"$PASS\n\"
sleep 2
log_user 1
}
$user_code
"
}
and then invoke it like:
ssh_cmd '
expect "#" {
send pwd\r
send exit\r
}
expect eof
'
Note that single quotes have no special meaning in expect, they are just plain characters: you probably don't want to expect the prompt to be the 3 character pattern '#'
Given the very simple script script.expect
#!/usr/bin/expect
spawn bash
expect "#"
send "/bin/false; echo \"process returned with $?\"\r"
expect -exact "process returned with 0"
send -- "exit\r"
expect eof
I don't seem to be able how the script can not fail since /bin/false will cause the echo command to print process returned with 1, thus process returned with 0 can never be matched on the expect command. I expect expect script.expect to fail with return code 1 after expect -exact "process returned with 0".
#!/usr/bin/expect
spawn bash
expect "#"
send "/bin/true; echo \"process returned with $?\"\r"
expect -exact "process returned with 0" {
send -- "exit\r"
expect eof
exit 0
}
exit 1
Even if I change the logic of my "application" in order to be able to test it with a positive/logically negated flow the outcome is still unexplainable.
I worked through
How to make expect command in expect program script to wait for exact string matching
https://www.thegeekstuff.com/2010/10/expect-examples
https://unix.stackexchange.com/questions/66520/error-handling-in-expect
https://unix.stackexchange.com/questions/79310/expect-script-within-bash-exit-codes?rq=1
and have no clue why expect is behaving this way.
In your first script, the expect -exact... command is "succeeding" with a timeout. The default timeout is 10 seconds, and the default action on timeout is to do nothing. So the commands waits 10 seconds, matches timeout, and returns, so we continue with the next command.
You can explicitly match for timeout:
expect {
-exact "process returned with 0" {}
timeout { puts "timeout!"; exit 1 }
}
To avoid the wait to timeout, you can use a regexp that will match whether $? is 0 or 1 (or other numbers). If you put part of the regexp in a capture group (), you can then find it in built-in variable $expect_out(1,string):
expect -re {process returned with ([0-9]+)}
set returncode $expect_out(1,string)
puts "we got $returncode"
exit $returncode
Note, the regexp uses {} style quotes, because "" quotes dont allow you to use [] inside them.
I am not quite sure if it a good idea to create a new Thread or "reopen" this 3-year old Thread, if you think it's better to reopened it, please excuse my spam in this Forum but I have the same Problem and don't get a solution out of the information of the thread. At the Moment I had a script that looks like this:
#!/usr/bin/expect -f
set pass [lindex $argv 0]
spawn <CMD>
expect {
-re "Password: " {
send "$pass\r"
}
expect eof
catch wait result
}
exit [lindex $result 3]
but wenn I execute this Script I get the error
can't read "result": no such variable
while executing
"lindex $result 3"
invoked from within
"exit [lindex $result 3]"
(file "./call_tests.exp" line 13)
I already found out that probably the problem is that the SSH-Session is already closed when I try to read the exit code. But I started yesterday to understand the expect-command so I am a complete newbie and I would very thanks full if someone can help me out.
best regards
Dan
You should write like this:
expect {
-re "Password: " {
send "$pass\r"
}
}
expect eof
catch wait result
exit [lindex $result 3]
or this:
expect {
-re "Password: " {
send "$pass\r"
exp_continue
}
eof {
catch wait result
}
}
exit [lindex $result 3]
According to expect's man page:
expect [[-opts] pat1 body1] ... [-opts] patn [bodyn]
waits until one of the patterns matches the output of a spawned
process, a specified time period has passed, or an end-of-file
is seen. If the final body is empty, it may be omitted.
Patterns from the most recent expect_before command are implicitly used before any other patterns. Patterns from the most
recent expect_after command are implicitly used after any other
patterns.
If the arguments to the entire expect statement require more
than one line, all the arguments may be braced into one so as
to avoid terminating each line with a backslash. In this one
case, the usual Tcl substitutions will occur despite the braces.
I'm including simple Expect commands within a Bash script (I know I could be just writing a pure Expect script, but I would like to get it to work from within Bash).
The script is below:
#!/bin/bash
OUTPUT=$(expect -c '
spawn ssh mihail911#blah.org
expect "password:"
send "dog\r"
')
Upon ssh'ing to the above address, it will return something of the form mihail911's password: on the prompt, so I think my expect line is valid.
When I run this my script does not print anything. It does not even show the password: prompt. In general, even if I manually provide an incorrect password, I will receive a Incorrect password-type response prompt. Why is nothing printing and how can I get my script to execute properly?
I have tried debugging by using the -d flag and it seems to show that at least the first expect prompt is being matched properly.
In addition, what values should I expect in the OUTPUT variable? When I echo this variable, it simply prints the first the first command of the expect portion of the script and then mihail911's password:. Is this what it's supposed to be printing?
Use:
#!/bin/bash
OUTPUT=$(expect -c '
# To suppress any other form of output generated by spawned process
log_user 0
spawn ssh dinesh#xxx.xxx.xx.xxx
# To match some common prompts. Update it as per your needs.
# To match literal dollar, it is escaped with backslash
set prompt "#|>|\\$"
expect {
eof {puts "Connection rejected by the host"; exit 0}
timeout {puts "Unable to access the host"; exit 0;}
"password:"
}
send "root\r"
expect {
timeout {puts "Unable to access the host"; exit 0;}
-re $prompt
}
send "date\r"
# Matching only the date cmd output alone
expect {
timeout { puts "Unable to access the host";exit 0}
-re "\n(\[^\r]*)\r"
}
send_user "$expect_out(1,string)\n"
exit 1
')
echo "Expect's return value: $?"; # Printing value returned from 'Expect'
echo "Expect Output: $OUTPUT"
Output:
dinesh#MyPC:~/stackoverflow$ ./Meric
Expect's return value: 1
Expect Output: Wed Sep 2 09:35:14 IST 2015
dinesh#MyPC:~/stackoverflow$
I am using expect within bash. I want my script to telnet into a box, expect a prompt, send a command. If there is a different prompt now, it has to proceed or else it has to send that command again.
My script goes like this:
\#!bin/bash
//I am filling up IP and PORT1 here
expect -c "
set timeout -1
spawn telnet $IP $PORT1
sleep 1
send \"\r\"
send \"\r\"
set temp 1
while( $temp == 1){
expect {
Prompt1 { send \"command\" }
Prompt2 {send \"Yes\"; set done 0}
}
}
"
Output:
invalid command name "while("
while executing
"while( == 1){"
Kindly help me.
I tried to change it to while [ $temp == 1] {
I am still facing the error below:
Output:
invalid command name "=="
while executing
"== 1"
invoked from within
"while [ == 1] {
expect {
This is how I'd implement this:
expect -c '
set timeout -1
spawn telnet [lindex $argv 0] [lindex $argv 1]
send "\r"
send "\r"
expect {
Prompt1 {
send "command"
exp_continue
}
Prompt2 {
send "Yes\r"
}
}
}
' $IP $PORT1
use single quotes around the expect script to protect expect variables
pass the shell variables as arguments to the script.
use "exp_continue" to loop instead of an explicit while loop (you had the wrong terminating variable name anyway)
The syntax for while is "while test body". There must be a spce between each of those parts which is why you get the error "no such command while)"
Also, because of tcl quoting rules, 99.99% of the time the test needs to be in curly braces. So, the syntax is:
while {$temp == 1} {
For more information see http://tcl.tk/man/tcl8.5/TclCmd/while.htm
(you probably have other problems related to your choice of shell quotes; this answer addresses your specific question about the while statement)