I have a script which solicits a numeric input from the user while booting the computer. The computer is running Fedora 16. It used work, on Fedora 13, but after the upgrade
read INTEGER
returns immediately, without catching any user input. I tried
read INTEGER
wait $!
but (predictably) that too doesn't work. The script is run from a systemd service file (see comments below). It must be run as root, and must started before the user logs in. It currently calls bash as its interpreter, but with some effort, that could be changed. Can anyone help return this script to normal?
Extra credit: In F13, it used to halt booting for user input (as desired) but the input was not displayed as the user typed. Is there a way to add this functionality?
During a normal boot, the keyboard is connected to Plymouth (I believe)
On Fedora, I believe you want something like:
plymouth ask-question --prompt="Pick a number between 0 and ∞" \
--command="/usr/bin/numberguesser"
possibly with
--dont-pause-progress
That should display the Plymouth prompt screen, not dissimilar from the way that crypto filesystems prompt for their passwords.
Note that /usr/bin/numberguesser would only get the string entered piped in on its standard input.
Untested, sorry :-(
Related
I'm using go's exec Run command to get command output, which works great when the command 'Stdout' field is set to os.Stdout, and the error is sent to os.Stderr.
I want to display the output and the error output to the console, but I also want my program to see what the output was.
I then made my own Writer type that did just that, wrote both to a buffer and printed to the terminal.
Here's the problem—some applications change their output to something much less readable by humans when it detects it's not writing to a tty. So the output I get changes to something ugly when I do it in the latter way. (cleaner for computers, uglier for humans)
I wanted to know if there was some way within Go to convince whatever command I'm running that I am a tty, despite not being os.Stdout/os.Stderr. I know it's possible to do using the script bash command, but that uses a different flag depending on Darwin/Linux, so I'm trying to avoid that.
Thanks in advance!
The only practical way to solve this is to allocate a pseudo terminal (PTY) and make your external process use it for its output: since PTY is still a terminal, a process checking whether it's connected to a real terminal thinks it is.
You may start with this query.
The github.com/creack/ptyis probably a good starting point.
The next step is to have a package implementing a PTY actually allocate it, and connect "the other end" of a PTY to your custom writer.
(By the way, there's no point in writing a custom "multi writer" as there exist io.MultiWriter).
(Please, help me adjust title and tags.)
When I run connmanctl I get a different prompt,
enrico:~$ connmanctl
connmanctl>
and different commands are available, like services, technologies, connect, ...
I'd like to know how this thing works.
I know that, in general, changing the prompt can be just a matter of changing the variable PS1. However this thing alone (read "the command connmanctl changes PS1 and returns) wouldn't have any effect at all on the functionalities of the commands line (I would still be in the same bash process).
Indeed, the fact that the available commands are changed, looks to me like the proof that connmanctl is running all the time the prompt is connmanctl>, and that, upon running connmanctl, a while loop is entered with a read statement in it, followed by a bunch of commands which process the the input.
In this latter scenario that I imagine, there's not even need to change PS1, as the connmanctl> line could simply be obtained by echo -n "connmanctl> ".
The reason behind this curiosity is that I'm trying to write a wrapper to connmanctl. I've already written it, and it works as intended, except that I don't know how to properly setup the autocompletion feature, and I think that in order to do so I first need to understand what is the right way to write an interactive shell script.
How can I capture the input/ output from a script in realtime (such as with tee), but line-by-line instead of character-by-character? My goal is to capture the input typed into the interactive prompts of a script only after backspaces and auto-completion have finished processing (after the RETURN key is hit).
Specifically, I am trying to create a wrapper script for ssh that creates a timestamped log of commands used on remote servers. The script, which uses tee to redirect the output for filtering, works well, but the redirected output gets jumbled with unsubmitted characters whenever I use the backspace key or the up/down keys to scroll through my remote history. For example: service test stopexitservice test stopart or cd ..logs[1Pls -al.
Perhaps there is a way to capture the terminal's scrollback and redirect that like with tee?
Update: I have found a character-based cleanup solution that does what I want most of the time. However, I am still hoping for an answer to this question (which may well be msw's answer that it is very difficult to do).
In the Unix world there are two primary modes of handling keyboard input. These are known as 'raw' in which characters are passed from the terminal to the reading program one at a time. This is the mode that editors (and such) will use because the editor needs to respond immediately when you press a key.
The other terminal discipline is called 'cooked' which is the line by line behavior that you think of as the bash line by line input where you get to backspace and the command is not executed until you press return. Ssh has to take your input in raw, character-by-character mode because it has no idea what is running on the other side. For example, if you are running an editor on the far side, it can't wait for a return before sending the key-press. So, as some have suggested, grabbing shell history on the far side is the only reasonable way to get a command-by-command record of the bash commands you typed.
I oversimplified for clarity; actually most installations of bash take input in raw mode because they allow editor like command modification. For example, Ctrl-P scrolls up the command history or Ctrl-A goes to the beginning of the line. And bash needs to be able to get those keys the moment they are typed not waiting for a return.
This is another reason that capturing on the local side is obnoxiously difficult: if you capture on the local side, the stream will be filled with Backspaces and all of bash's editing commands. To get a true transcript of what the remote shell actually executed you have to parse the character stream as if you were the remote shell. There also a problem if you run something like
vi /some_file/which_is_on_the_remote/machine
the input stream to the local ssh will be filled with movement commands snippets of text including backspaces and so on and it would be bloody difficult to figure out what is part of a bash command and what is you talking to the editor.
Few things involving computers are impossible; getting clean input from the local side of an ssh invocation is really, really hard.
I question the actual utility of recording the commands that you execute on a local or remote machine. The reason is that there is so much state which is not visible from a command log. As a simple example here's a log of two commands:
17:00$ cp important_file important_file.bak
17:15$ rm important_file
and two days later you are trying to figure out whether important_file.bak should have the contents you intended or not. Given that log you can't answer that simple question. Even if you had the sequence
16:58$ cat important_file
17:00$ cp important_file important_file.bak
17:15$ rm important_file
If you aren't capturing the output, the cat in the log will not tell you anything. Give me almost any command sequence and I can envision a scenario in which it will not give you the information you need to make sense of what was done.
For a very similar purpose I use GNU screen which offer the option to record everything you do in a shell session (INPUT/OUTPUT). The log it creates also comes with undesirable characters but I clean them with perl:
perl -ne 's/\x1b[[()=][;?0-9]*[0-9A-Za-z]?//g;s/\r//g;s/\007//g;print' < screenlog.0
I hope this helps.
Some features of screen:
http://speaking-my-language.blogspot.com/2010/09/top-5-underused-gnu-screen-features.html
Site I found the perl-oneliner:
https://superuser.com/questions/99128/removing-the-escape-characters-from-gnu-screens-screenlog-n
I have a serial usb device that is connected to a linux box and it works fine with serial communication programs, such as minicom.
For instance, within that program, I send the string "V" and I get back an answer: "UBW FW D Version 1.4.3".
Now, I'd like to do a shell script that could do the same, in order to test variables. I investigated the possibility to use minicom without being "interactive" but it seems is not possible. I also tried the obvious "echo V > /dev/ttyACM0" but had no luck as well.
Any idea of how can I send and receive strings to/from a serial device in such way I can use the received data in a shell script?
Thanks
In the olden days of modems, we would use the program 'expect' to send and receive data from the serial line. This doesn't exactly solve your problem, but might get you some of the way there.
Have a look at Use expect in bash script to provide password to SSH command
The atinout program does exactly what you are asking for. Example:
$ echo AT | atinout - /dev/ttyACM0 -
AT
OK
$
Now, from you example command and response, I see that your "modem" seems to able to configure or modify to not return the OK Final Result Code, and atinout absolutely needs that for its operation, so make sure the UBW behaves properly.
I'm new to programming/development and I'm having trouble installing development tools.One of my biggest problems when installing something is understanding the shell or terminal (are they the same thing?) and how it relates to installing tools like uncrustify for example. What do I need to read to understand the shell/terminal and $PATH?
Have you tried Googling?
Environment variable
PATH (variable)
(I think you're getting good advice so far on PATH)
The most generic description of a shell is that is a program that facilitates interaction w programs. Programs facilitate 'communication' with the OS to perform work by the hardware.
There are two modes that you will normally interact with a shell.
a command-line processor, where you type in commands, letter-by-letter, word-by-word until you press the enter key. Then the shell will read what you have typed, validate that it understands the general form of what you have asked for, and then start running the 1 (or more) programs specified in what you have typed.
a batch-script processor. In this case you have assembled all of the commands you want executed into a file, and then thru 1 of several mechanisms, you arrange to have the batch-script run so it will in turn run the commands you have specified and the computer does your work for you. Have you done a Windows .Bat file? same idea, but more powerful.
So, a terminal widow is program that is responsible for a. getting input and b., printing output. When you get to the c-programming that underlies the Unix system, you are talking about a feature of the OS design which are called Standard In and Standard Out. Normal unix commands expect to read instructions from StdIn and print output to StdOut.
Of course, all good programs can get their input from files and write there output to files as well, and most programs will take over the StdIn/Out and process files instead of reading input from the keyboard and/or writing to the screen.
To return to the shell, this program that lets you type while the terminal window is open. There are numerous versions of the shell that you may run into AND have varying levels of features that support a. interactive-mode, b. batch-script mode.
To sum it up, here a diagram of what is involved (very basically) for terminal and shell
(run a) terminal-window (program)
shell-command-prompt (program) (automatically started as subprogram)
1. enter commands one at a time, with input from
a. typed at keyboard (std-in)
b. infile
and output to
a. screen (std-out)
b. outFile
program
calls OS level functions for
a. computation
b. I/O
OR 2.
(run the shell program without a terminal, usually from the cron sub-system)
shell-batch-processor
shell program reads batch-script file, 1 'statement' at a time
validate statements
run program, relying on script or cfg to provide inFile data and
indicate where to put outfile data.
I hope this helps.