How to loop a command until a return value =0 in a sh script?
I need to run a ftp upload many times until this works (return value=0) maybe with a little sleep command.
This should do the job:
until command here; do; done
You may want to sleep inside to not DoS the server or waste a lot of bandwidth:
until command here; do sleep 1; done
If your command contains semicolons, parenthesise it.
Related
I would like to execute any bash command. I found Command::new but I'm unable to execute "complex" commands such as ls ; sleep 1; ls. Moreover, even if I put this in a bash script, and execute it, I will only have the result at the end of the script (as it is explain in the process doc). I would like to get the result as soon as the command prints it (and to be able to read input as well) the same way we can do it in bash.
Command::new is indeed the way to go, but it is meant to execute a program. ls ; sleep 1; ls is not a program, it's instructions for some shell. If you want to execute something like that, you would need to ask a shell to interpret that for you:
Command::new("/usr/bin/sh").args(&["-c", "ls ; sleep 1; ls"])
// your complex command is just an argument for the shell
To get the output, there are two ways:
the output method is blocking and returns the outputs and the exit status of the command.
the spawn method is non-blocking, and returns a handle containing the child's process stdin, stdout and stderr so you can communicate with the child, and a wait method to wait for it to cleanly exit. Note that by default the child inherits its parent file descriptor and you might want to set up pipes instead:
You should use something like:
let child = Command::new("/usr/bin/sh")
.args(&["-c", "ls sleep 1 ls"])
.stderr(std::process::Stdio::null()) // don't care about stderr
.stdout(std::process::Stdio::piped()) // set up stdout so we can read it
.stdin(std::process::Stdio::piped()) // set up stdin so we can write on it
.spawn().expect("Could not run the command"); // finally run the command
write_something_on(child.stdin);
read(child.stdout);
how to declare variable in bash command. See "?"
I thought we could almost run any bash statement with ! or host in front of line
#!/bin/bash
sqlplus scott/tiger#orcl << EOF
! export v10="Hi" Doesn't work, why?
! echo $v10 Doesn't work, why?
! echo "Done" Works perfectly and also other bash commands
select * from dept; Works perfectly
exit
EOF
Thank you
What #jordanm says "probably" is exactly what is happening. When you specify a host command from within sqlplus, a separate shell process is spawned, the command executed by that process, then that process is terminated and control returns to sqlplus. Any environment variables that are set in that child shell process are good only within it, so when it terminates, they are gone.
As for your specific lines that "work" and "don't work" .. "export v10="Hi" does work but there is no stdout display of the 'export' command, and as explained, that variable v10 ceases to exist once the child process completes and control returns to sqlplus. The "echo $v10" also works, but since that is a new shell process, it has no value for $v10, so there is nothing to echo.
What are you trying to accomplish by setting enviornment variables from within sqlplus?
found it, all I had to do was
<< EOF
whenever sqlerror exit failure rollback
whenever oserror exit failure rollback
#scriptname.sql
EXIT
EOF
I want to use the pidof by a process given by name in tcl. I have used [exec pidof $proc_name ], but it always returns an error: child process exited abnormally.
I read somewhere exec always treat non-zero return as error as pidof return the process id number. Does anyone know if there is a workaround? Thanks in advance!
I want to use pidof is that i want to see if that process is running if not i will restart the process.
The problem is that pidof does strange things with exit codes:
Exit Status
At least one program was found with the requested name.
No program was found with the requested name.
This interacts badly with exec which treats a non-zero exit code as indicating that it should tell the rest of Tcl that there was an error.
The simplest way of dealing with this is a little extra shell script wrapper. Let's hide it inside a procedure for convenience:
proc pidof {name} {
exec /bin/bash -c "pidof '$name'; exit \$(( \$? - 1 ))"
}
All that does is subtract 1 from the exit code before it hits back into Tcl.
(You could also fix this using the techniques described in the exec manual but I think it's simpler to fix on the bash side this time.)
I ran into this and ended up causing some issues with the old linux environment I run in (no bash and exit code handling was a bit different with busybox).
My solution that should work anywhere would be similar to what a few suggested:
proc pidof {name} {
catch {exec -ignorestderr -- pidof $name} pid
if {[string is entier -strict $pid]} {
return $pid
}
}
I have an expect script which I need to run every 3 mins on my management node to collect tx/rx values for each port attached to DCX Brocade SAN Switch using the command #portperfshow#
Each time I try to use crontab to execute the script every 3 mins, the script does not work!
My expect script starts with #!/usr/bin/expect -f and I am calling the script using the following syntax under cron:
3 * * * * /usr/bin/expect -f /root/portsperfDCX1/collect-all.exp sanswitchhostname
However, when I execute the script (not under cron) it works as expected:
root# ./collect-all.exp sanswitchhostname
works just fine.
Please Please can someone help! Thanks.
The script collect-all.exp is:
#!/usr/bin/expect -f
#Time and Date
set day [timestamp -format %d%m%y]
set time [timestamp -format %H%M]
#logging
set LogDir1 "/FPerf/PortsLogs"
et timeout 5
set ipaddr [lrange $argv 0 0]
set passw "XXXXXXX"
if { $ipaddr == "" } {
puts "Usage: <script.exp> <ip address>\n"
exit 1
}
spawn ssh admin#$ipaddr
expect -re "password"
send "$passw\r"
expect -re "admin"
log_file "$LogDir1/$day-portsperfshow-$time"
send "portperfshow -tx -rx -t 10\r"
expect timeout "\n"
send \003
log_file
send -- "exit\r"
close
I had the same issue, except that my script was ending with
interact
Finally I got it working by replacing it with these two lines:
expect eof
exit
Changing interact to expect eof worked for me!
Needed to remove the exit part, because I had more statements in the bash script after the expect line (calling expect inside a bash script).
There are two key differences between a program that is run normally from a shell and a program that is run from cron:
Cron does not populate (many) environment variables. Notably absent are TERM, SHELL and HOME, but that's just a small proportion of the long list that will be not defined.
Cron does not set up a current terminal, so /dev/tty doesn't resolve to anything. (Note, programs spawned by Expect will have a current terminal.)
With high probability, any difficulties will come from these, especially the first. To fix, you need to save all your environment variables in an interactive session and use these in your expect script to repopulate the environment. The easiest way is to use this little expect script:
unset -nocomplain ::env(SSH_AUTH_SOCK) ;# This one is session-bound anyway
puts [list array set ::env [array get ::env]]
That will write out a single very long line which you want to put near the top of your script (or at least before the first spawn). Then see if that works.
Jobs run by cron are not considered login shells, and thus don't source your .bashrc, .bash_profile, etc.
If you want that behavior, you need to add it explicitly to the crontab entry like so:
$ crontab -l
0 13 * * * bash -c '. .bash_profile; etc ...'
$
I'm betting that someone has already solved this and maybe I'm using the wrong search terms for google to tell me the answer, but here is my situation.
I have a script that I want to run, but I want it to run only when scheduled and only one at a time. (can't run the script simultaneously)
Now the sticky part is that say I have a table called "myhappyschedule" which has the data I need and the scheduled time. This table can have multiple scheduled times even at the same time, each one would run this script. So essentially I need a queue of each time the script fires and they all need to wait for each one before it to finish. (sometimes this can take just a minute for the script to execute sometimes its many many minutes)
What I'm thinking about doing is making a script that checks myhappyschedule every 5 min and gathers up those that are scheduled, puts them into a queue where another script can execute each 'job' or occurrence in the queue in order. Which all of this sounds messy.
To make this longer - I should say that I'm allowing users to schedule things in myhappyschedule and not edit crontab.
What can be done about this? File locks and scripts calling scripts?
add a column exec_status to myhappytable (maybe also time_started and time_finished, see pseudocode)
run the following cron script every x minutes
pseudocode of cron script:
[create/check pid lock (optional, but see "A potential pitfall" below)]
get number of rows from myhappytable where (exec_status == executing_now)
if it is > 0, exit
begin loop
get one row from myhappytable
where (exec_status == not_yet_run) and (scheduled_time <= now)
order by scheduled_time asc
if no such row, exit
set row exec_status to executing_now (maybe set time_started to now)
execute whatever command the row contains
set row exec_status to completed
(maybe also store the command output/return as well, set time_finished to now)
end loop
[delete pid lock file (complementary to the starting pid lock check)]
This way, the script first checks if none of the commands is running, then runs first not-yet run command, until there are no more commands to be run at the given moment. Also, you can see what command is executing by querying the database.
A potential pitfall: if the cron script is killed, a scheduled task will remain in "executing_now" state. That's what the pid lock at beginning and end is for: to see if the cron script terminated properly. pseudocode of create/check pidlock:
if exists pidlockfile then
check if process id given in file exists
if not exists then
update myhappytable set exec_status = error_cronscript_died_while_executing_this
where exec_status == executing_now
delete pidlockfile
else (previous instance still running)
exit
endif
endif
create pidlockfile containing cron script process id
You can use the at(1) command inside your script to schedule its next run. Before it exits, it can check myhappyschedule for the next run time. You don't need cron at all, really.
I came across this question while researching for a solution to the queuing problem. For the benefit of anyone else searching here is my solution.
Combine this with a cron that starts jobs as they are scheduled (even if they are scheduled to run at the same time) and that solves the problem you described as well.
Problem
At most one instance of the script should be running.
We want to cue up requests to process them as fast as possible.
ie. We need a pipeline to the script.
Solution:
Create a pipeline to any script. Done using a small bash script (further down).
The script can be called as
./pipeline "<any command and arguments go here>"
Example:
./pipeline sleep 10 &
./pipeline shabugabu &
./pipeline single_instance_script some arguments &
./pipeline single_instance_script some other_argumnts &
./pipeline "single_instance_script some yet_other_arguments > output.txt" &
..etc
The script creates a new named pipe for each command. So the above will create named pipes: sleep, shabugabu, and single_instance_script
In this case the initial call will start a reader and run single_instance_script with some arguments as arguments. Once the call completes, the reader will grab the next request off the pipe and execute with some other_arguments, complete, grab the next etc...
This script will block requesting processes so call it as a background job (& at the end) or as a detached process with at (at now <<< "./pipeline some_script")
#!/bin/bash -Eue
# Using command name as the pipeline name
pipeline=$(basename $(expr "$1" : '\(^[^[:space:]]*\)')).pipe
is_reader=false
function _pipeline_cleanup {
if $is_reader; then
rm -f $pipeline
fi
rm -f $pipeline.lock
exit
}
trap _pipeline_cleanup INT TERM EXIT
# Dispatch/initialization section, critical
lockfile $pipeline.lock
if [[ -p $pipeline ]]
then
echo "$*" > $pipeline
exit
fi
is_reader=true
mkfifo $pipeline
echo "$*" > $pipeline &
rm -f $pipeline.lock
# Reader section
while read command < $pipeline
do
echo "$(date) - Executing $command"
($command) &> /dev/null
done