I realized that I've spent more time on this issue than necessary, hence the question.
Sometimes I need to save the last typed shell command into the clipboard.
I can do something like this:
echo !! | xsel --clipboard
Which works successfully.
But when I try to alias the above command:
alias echoxs='echo !! | xsel --clipboard'
Things do not work as expected. In particular, the clipboard contents become literally !!. Obviously, I am missing something about how bash preprocesses commands and aliases. My hope was that an alias, as is intuitive, would be something like a C macro, and that typing the alias would be equivalent to typing its target.
I've tried other approaches and none seem to work. Using HISTFILE inside a script does not work because either commands are cached by the shell session and not immediately written to the file, or multiple terminals mess with the file such that the last command in the file is not always reliably the last command in the current session.
alias='history 1 | xsel --clipboard'
Almost works, except all fails when attempting to modify (eg, cut or sed) the output of history because it is a built-in command.
Is the a way to get the shell's last command through sane stdout?
I'm not sure to understand what you said about "failing when attempting to modify the output of history", so I hope my solution will suit you. I'm using fc to get the last command:
fc -ln -1 | xsel --clipboard
Here are the meaning of the options:
l is to use the standard output
n is to hide the command history number
-1 is to get the last command from the history
Client: pass the option -XY to the ssh command to enable (trusted) X11 forwarding for this session:
ssh -XY USER#IP
Server: check /etc/ssh/sshd_config to make sure X11 forwarding is enabled on server
X11Forwarding yes
yum install xclip -y
echo `hostname -I` `hostname` >> /etc/hosts
echo "alias cplastcmd='history 2 | cut -c 8- | head -n 1 | xclip -selection clipboard'" >> ~/.bashrc
Restart bash and type cplastcmd to copy last bash command to clipboard via X11.
Related
I need to capture the output of a bash command which prompts for a user's confirmation without altering its flow.
I know only 2 ways to capture a command output:
- output=$(command)
- command > file
In both cases, the whole process is blocked without any output.
For instance, without --assume-yes:
output=$(apt purge 2>&1 some_package)
I cannot print the output back because the command is not done yet.
Any suggestion?
Edit 1: The user must be able to answer the prompt.
EDIT 2: I used dash-o's answer to complete a bash script allowing a user to remove/purge all obsolete packages (which have no installation candidate) from any Debian/Ubuntu distribution.
To capture partial output from that is waiting for a prompt, one can use a tail on temporary file, potentiality with 'tee' to keep the output flowing if needed. The downside of this approach is that stderr need to be tied with stdout, making it hard to tell between the two (if this is an issue)
#! /bin/bash
log=/path/to/log-file
echo > $log
(
while ! grep -q -F 'continue?' $log ; do sleep 2 ; done ;
output=$(<$log)
echo do-something "$output"
) &
# Run command with output to terminal
apt purge 2>&1 some_package | tee -a $log
# If output to terminal not needed, replace above command with
apt purge 2>&1 some_package > $log
There is no generic way to tell (from a script) when exactly a program prompts for input. The above code looks for the prompt string ('continue?'), so this will have to be customized per command.
It seems that when my screen is locked for some period of time, my S.gpg-agent.ssh disappears, and so in order to continue using my key I have to re-initialise it.
Obviously, this is a relatively frequent occurrence, so I've written a function for my shell to kill gpg-agent, restart it, and reset the appropriate environment variables.
This may be a bit of an 'X-Y problem', X being above this line, but I think Y below is more generally useful to know anyway.
How can I automatically run a command when an extant file no longer exists?
The best I've come up with is:
nohup echo "$file" | entr $command &
at login. But entr runs a command when files change, not just deletion, so it's not clear to me how that will behave with a socket.
According to your comment, cron daemon does not fit.
Watch socket file deletion
Try auditd
# auditctl -w /var/run/<your_socket_file> -p wa
$ tail -f /var/log/audit/audit.log | grep 'nametype=DELETE'
Howto run a script if event occurred
If you want to run a script on socketile deletion, you can use while loop, e.g.:
tail -Fn0 /var/log/audit/audit.log | grep 'name=<your_socket_file>' | grep 'nametype=DELETE' \
while IFS= read -r line; do
# your script here
done
thx to Tom Klino and his answer
You don't mention the OS you're using, but if it's linux, you can use inotifywait from the inotify-tools package:
#!/bin/sh
while inotifywait -qq -e delete_self /path/to/S.gpg-agent.ssh; do
echo "Socket was deleted!"
# Recreate it.
done
Abstract: How to run an interactive task in background?
Details: I am trying to run this simple script under ash shell (Busybox) as a background task.
myscript.sh&
However the script stops immediately...
[1]+ Stopped (tty input) myscript.sh
The myscript.sh contents... (only the relvant part, other then that I trap SIGINT, SIGHUP etc)
#!/bin/sh
catpid=0
START_COPY()
{
cat /dev/charfile > /path/outfile &
catpid = $!
}
STOP_COPY()
{
kill catpid
}
netcat SOME_IP PORT | while read EVENT
do
case $EVENT in
start) START_COPY;;
stop) STOP_COPY;;
esac
done
From simple command line tests I found that bot cat and netcat try to read from tty.
Note that this netcat version does not have -e to supress tty.
Now what can be done to avoid myscript becoming stopped?
Things I have tried so for without any success:
1) netcat/cat ... < /dev/tty (or the output of tty)
2) Running the block containing cat and netcat in a subshell using (). This may work but then how to grab PID of cat?
Over to you experts...
The problem still exists.
A simple test for you all to try:
1) In one terminal run netcat -l -p 11111 (without &)
2) In another terminal run netcat localhost 11111 & (This should stop after a while with message Stopped (TTY input) )
How to avoid this?
you probably want netcat's "-d" option, which tells it not to read from STDIN.
I can confirm that -d will help netcat run in the background.
I was seeing the same issue with:
nc -ulk 60001 | nc -lk 60002 &
Every time I queried the jobs, the pipe input would stop.
Changing the command to the following fixed it:
nc -ulkd 60001 | nc -lk 60002 &
Are you sure you've given your script as is or did you just type in a rough facsimile meant to illustrate the general idea? The script in your question has many errors which should prevent it from ever running correctly, which makes me wonder.
The spaces around the = in catpid=$! make the line not a valid variable assignment. If that was in your original script I am surprised you were not getting any errors.
The kill catpid line should fail because the literal word catpid is not a valid job id. You probably want kill "$catpid".
As for your actual question:
cat should be reading from /dev/charfile and not from stdin or anywhere else. Are you sure it was attempting to read tty input?
Have you tried redirecting netcat's input like netcat < /dev/null if you don't need netcat to read anything?
I have to use a netcat that doesn't have the -d option.
"echo -n | netcat ... &" seems to be an effective workaround: i.e. close the standard input to netcat immediately if you don't need to use it.
As it was not yet really answered, if using Busybox and -d option is not available, the following command will keep netcat "alive" when sent to background:
tail -f /dev/null | netcat ...
netcat < /dev/null and echo -n | netcat did not work for me.
Combining screen and disown-ing process work for me, as '-d' option is not a valid anymore for netcat. Tried redirecting like nc </dev/null but session ends prematurely (as I need -q 1 to make sure nc process stop as file transfer finished)
Setup Receiver side first,
on Receiver side, screen keep stdin for netcat so it won't terminated
EDIT: I was wrong, you need to enter command INSIDE screen. You'll end with no file saved, or weird binary thing flow in your terminal while attach to screen, if you redirecting nc inline of screen command. (Example, this is THE WRONG WAY: screen nc -l -p <listen port> -q 1 > /path/to/yourfile.bin)
Open screen , then press return/Enter on welcome message. new blank shell will appear (you're inside screen now)
type command: nc -l -p 1234 > /path/to/yourfile.bin
then, press CTRL + a , then press d to detach screen.
on Sender sides, disown process, quit 1s after reaching EOF
cat /path/to/yourfile.bin | nc -q1 100.10.10.10 1234 & disown
I want to run a few tasks in shell.
tail a file into a new file: for example: tail -f debug|tee -a test.log
at the same time, run other tasks.
My question is: how to make the command tail -f debug|tee -a test.log run in background, so that I can run other tasks then in shell script?
You don't need tee at all for this, just use the shell's built-in append operator:
tail -f debug >> test.log &
The trailing & works as normal in the shell. You only need tee to send the output to a file as well as standard out, which if you have it in the background probably isn't what you want.
Normally you just use an ampersand after the command if you want to background something.
tail -f debug|tee -a test.log &
Then you can bring it back to the foreground later by typing fg. Did this answer your question or have I missed what you were asking?
The simple way to do this is:
screen -R -D
tail -f debug|tee -a test.log
Ctrl-A c
ps ax |grep tail
Ctrl-A [Backspace]
...
Ctrl-A [Spacebar]
screen lets you run multiple terminal sessions on one terminal connection. You switch back and forth with Ctrl-A [Backspace]|[Space]. To create another separate shell Ctrl-A c
A major benefit of screen is that if the terminal session disconnects, it keeps everything runnning. Just close the terminal window or disconnect ssh, go to another computer, log in and run screen -R -D to reconnect to everything which is still running.
If you only occasionally need this, just run tail, type Ctrl-Z, run a command, then fg %1 to bring the tail process back into the foreground, or bg %1 to make it run in the background permanently. If you do use Ctrl-Z, then the jobs command shows all of your detached jobs.
This is what was trying to do:
$ wget -qO- www.example.com/script.sh | sh
which quietly downloads the script and prints it to stdout which is then piped to sh. This unfortunately doesn't quite work, failing to wait for user input at various points, aswell as a few syntax errors.
This is what actually works:
$ wget -qOscript www.example.com/script.sh && chmod +x ./script && ./script
But what's the difference?
I'm thinking maybe piping the file doesn't execute the file, but rather executes each line individually, but I'm new to this kind of thing so I don't know.
When you pipe to sh , stdin of that shell/script will be the pipe. Thus the script cannot take e.g. user input from the console. When you run the script normally, stdin is the console - where you can enter input.
You might try telling the shell to be interactive:
$ wget -qO- www.example.com/script.sh | sh -i
I had the same issue, and after tinkering and googling this is what worked for me.
wget -O - www.example.com/script.sh | sh