I'm looking for something like command1 ; command2 i.e. how to run command2 after command1 but I'd like to plan execution of command2 when command1 is already running.
It can be solved by just typing the command2 and confirming by Enter supposed that the command1 is not consuming standard input and that the command1 doesn't produce to much text on output making it impractical to type (typed characters are blended with the command1 output).
Generally what I do is: Ctrl+Z fg && command2
bg, to resume command1 in the background while you type out command2.fg && command2 to resume command1 in the foreground and queue up command2 afterwards if command1 succeeds. You can of course substitute ; or || for the && if you so desire.start a command
command1
pause the execution by pressing Ctrl+Z
find the job number of the paused command (it's usually already printed to console when to console when to command is paused) by executing
jobs
let command1 continue in background
bg
plan execution of command2 to await finish of command1
wait -n <command1 job number> ; command2
Documentation Job Control Builtins
fg ; command. Or even fg && command to only run the 2nd command / pipeline if the first one was successful. (You can still use bg while thinking / typing, if it doesn't spew text on the terminal.)
command1; command2 syntax. Could you please clarify this for me?
command1 & proceed_after=$! then when you've got the next command figured out wait -n $proceed_after; command 2
There are several alternatives.
With one ampersand, 'push to background', the second program starts after the first one starts, but they will probably run alongside each other.
command1 & command2
With two ampersands, 'logical and', the second program will start only if the first program finished successfully.
command1 && command2
With a semicolon separating the commands in the command line, the the second program will start, when the first program finished, even if it failed or was interrupted.
command1 ; command2
You can use wait <PID> to wait for the first command to finish, if it is already running from the same shell (in the same terminal window).
Otherwise if the first command is already running from another shell (in another window), you can use a small while loop using ps to check if the PID is still found by ps. When it is no longer found, the second command will be started.
This demo example for bash checks if top is running via the PID, and runs the command
echo "*** $USER, I am ready now ***"
if/when top is no longer running.
pid=$(ps -A|grep top|cut -d ' ' -f 1); \
while [ "$pid" != "" ]; do ps -A|grep "$pid" > /dev/null; \
if [ $? -eq 0 ]; then sleep 5;else pid=""; fi; done; \
echo "*** $USER, I am ready now ***"
The standard way is just to let command 1 start in the background and then have command 2 start either in the background or in the foreground. The full command is this:
command1 & command2
& is not a connector between these two commands. It can be used with command1 alone to have it started in the background:
command1 &
And this is right syntax for starting both commands in the background:
command1 & command2 &
;. Or do you want to do something while the first one is still running?
If you have a choice to use two terminals, here's what you can do:
ps -ef | grep <command1> (you might want to properly form the filter string in grep command so that you do not accidently find another process having as a substring).wait <command1_pid> ; command2Basically, wait is a bash built-in command that waits until the provided PIDs exit and then return. You are simply delegating your waiting for command1 to finish, on to bash's wait command.
wait in different terminal outputs following error message: bash: wait: pid 19531 is not a child of this shell.
wait system calls only work on child processes, so one bash process can't wait for the children of a different instance of bash. man7.org/linux/man-pages/man2/wait.2.html#ERRORS says wait and waitpid return with ECHILD error status in this case.