I've written a shell script to soft-restart HAProxy (reverse proxy). Executing the script from the shell works. But I want a daemon to execute the script. That doesn't work. system() returns 256. I have no clue what that might mean.
#!/bin/sh
# save previous state
mv /home/haproxy/haproxy.cfg /home/haproxy/haproxy.cfg.old
mv /var/run/haproxy.pid /var/run/haproxy.pid.old
cp /tmp/haproxy.cfg.new /home/haproxy/haproxy.cfg
kill -TTOU $(cat /var/run/haproxy.pid.old)
if haproxy -p /var/run/haproxy.pid -f /home/haproxy/haproxy.cfg; then
kill -USR1 $(cat /var/run/haproxy.pid.old)
rm -f /var/run/haproxy.pid.old
exit 1
else
kill -TTIN $(cat /var/run/haproxy.pid.old)
rm -f /var/run/haproxy.pid
mv /var/run/haproxy.pid.old /var/run/haproxy.pid
mv /home/haproxy/haproxy.cfg /home/haproxy/haproxy.cfg.err
mv /home/haproxy/haproxy.cfg.old /home/haproxy/haproxy.cfg
exit 0
fi
HAProxy is executed with user haproxy. My daemon has it's own user too. Both run with sudo.
Any hints?
According to this and that, Perl's system() returns exit values multiplied by 256. So it's actually exiting with 1. It seems this happens in C too.
Unless system returns -1 its return value is of the same format as the status value from the wait family of system calls (man 2 wait). There are macros to help you interpret this status:
man 3 wait
Lists these macros and what they tell you.
A code of 256 probably means that the system command cannot locate the binary to run it. Remember that it may not be calling bash and that it may not have paths setup. Try again with full paths to the binaries!
I have the same problem when call script that contains `kill' command in a daemon.
The daemon must have closed the stdout, stderr...
Use something like system("scrips.sh > /dev/null") should work.
Related
I have a script where I need to start a command, then pass some additional commands as commands to that command. I tried
su
echo I should be root now:
who am I
exit
echo done.
... but it doesn't work: The su succeeds, but then the command prompt is just staring at me. If I type exit at the prompt, the echo and who am i etc start executing! And the echo done. doesn't get executed at all.
Similarly, I need for this to work over ssh:
ssh remotehost
# this should run under my account on remotehost
su
## this should run as root on remotehost
whoami
exit
## back
exit
# back
How do I solve this?
I am looking for answers which solve this in a general fashion, and which are not specific to su or ssh in particular. The intent is for this question to become a canonical for this particular pattern.
Adding to tripleee's answer:
It is important to remember that the section of the script formatted as a here-document for another shell is executed in a different shell with its own environment (and maybe even on a different machine).
If that block of your script contains parameter expansion, command substitution, and/or arithmetic expansion, then you must use the here-document facility of the shell slightly differently, depending on where you want those expansions to be performed.
1. All expansions must be performed within the scope of the parent shell.
Then the delimiter of the here document must be unquoted.
command <<DELIMITER
...
DELIMITER
Example:
#!/bin/bash
a=0
mylogin=$(whoami)
sudo sh <<END
a=1
mylogin=$(whoami)
echo a=$a
echo mylogin=$mylogin
END
echo a=$a
echo mylogin=$mylogin
Output:
a=0
mylogin=leon
a=0
mylogin=leon
2. All expansions must be performed within the scope of the child shell.
Then the delimiter of the here document must be quoted.
command <<'DELIMITER'
...
DELIMITER
Example:
#!/bin/bash
a=0
mylogin=$(whoami)
sudo sh <<'END'
a=1
mylogin=$(whoami)
echo a=$a
echo mylogin=$mylogin
END
echo a=$a
echo mylogin=$mylogin
Output:
a=1
mylogin=root
a=0
mylogin=leon
3. Some expansions must be performed in the child shell, some - in the parent.
Then the delimiter of the here document must be unquoted and you must escape those expansion expressions that must be performed in the child shell.
Example:
#!/bin/bash
a=0
mylogin=$(whoami)
sudo sh <<END
a=1
mylogin=\$(whoami)
echo a=$a
echo mylogin=\$mylogin
END
echo a=$a
echo mylogin=$mylogin
Output:
a=0
mylogin=root
a=0
mylogin=leon
A shell script is a sequence of commands. The shell will read the script file, and execute those commands one after the other.
In the usual case, there are no surprises here; but a frequent beginner error is assuming that some commands will take over from the shell, and start executing the following commands in the script file instead of the shell which is currently running this script. But that's not how it works.
Basically, scripts work exactly like interactive commands, but how exactly they work needs to be properly understood. Interactively, the shell reads a command (from standard input), runs that command (with input from standard input), and when it's done, it reads another command (from standard input).
Now, when executing a script, standard input is still the terminal (unless you used a redirection) but the commands are read from the script file, not from standard input. (The opposite would be very cumbersome indeed - any read would consume the next line of the script, cat would slurp all the rest of the script, and there would be no way to interact with it!) The script file only contains commands for the shell instance which executes it (though you can of course still use a here document etc to embed inputs as command arguments).
In other words, these "misunderstood" commands (su, ssh, sh, sudo, bash etc) when run alone (without arguments) will start an interactive shell, and in an interactive session, that's obviously fine; but when run from a script, that's very often not what you want.
All of these commands have ways to accept commands by ways other than in an interactive terminal session. Typically, each command supports a way to pass it commands as options or arguments:
su root -c 'who am i'
ssh user#remote uname -a
sh -c 'who am i; echo success'
Many of these commands will also accept commands on standard input:
printf 'uname -a; who am i; uptime' | su
printf 'uname -a; who am i; uptime' | ssh user#remote
printf 'uname -a; who am i; uptime' | sh
which also conveniently allows you to use here documents:
ssh user#remote <<'____HERE'
uname -a
who am i
uptime
____HERE
sh <<'____HERE'
uname -a
who am i
uptime
____HERE
For commands which accept a single command argument, that command can be sh or bash with multiple commands:
sudo sh -c 'uname -a; who am i; uptime'
As an aside, you generally don't need an explicit exit because the command will terminate anyway when it has executed the script (sequence of commands) you passed in for execution.
If you want a generic solution which will work for any kind of program, you can use the expect command.
Extract from the manual page:
Expect is a program that "talks" to other interactive programs according to a script. Following the script, Expect knows what can be expected from a program and what the correct response should be. An interpreted language provides branching and high-level control structures to direct the dialogue. In addition, the user can take control and interact directly when desired, afterward returning control to the script.
Here is a working example using expect:
set timeout 60
spawn sudo su -
expect "*?assword" { send "*secretpassword*\r" }
send_user "I should be root now:"
expect "#" { send "whoami\r" }
expect "#" { send "exit\r" }
send_user "Done.\n"
exit
The script can then be launched with a simple command:
$ expect -f custom.script
You can view a full example in the following page: http://www.journaldev.com/1405/expect-script-example-for-ssh-and-su-login-and-running-commands
Note: The answer proposed by #tripleee would only work if standard input could be read once at the start of the command, or if a tty had been allocated, and won't work for any interactive program.
Example of errors if you use a pipe
echo "su whoami" |ssh remotehost
--> su: must be run from a terminal
echo "sudo whoami" |ssh remotehost
--> sudo: no tty present and no askpass program specified
In SSH, you might force a TTY allocation with multiple -t parameters, but when sudo will ask for the password, it will fail.
Without the use of a program like expect any call to a function/program which might get information from stdin will make the next command fail:
ssh use#host <<'____HERE'
echo "Enter your name:"
read name
echo "ok."
____HERE
--> The `echo "ok."` string will be passed to the "read" command
Using supervisord, how do I execute a command before running the program?
For example in the code below, I want a file to be created before starting the program. In the code below I am using tail -f /dev/null to simulate the background process but this could be any running program like '/path/to/application'.
I tried '&&' and this doesn't seem to work. The requirement is that the file has to be created first in order for the application to work.
[supervisord]
nodaemon=true
logfile=~/supervisord.log
[program:app]
command:touch ~a.c && tail -f /dev/null
The problem is that supervisor isn't running a shell to interpret command sections, so "&&" is just one of 5 space separated arguments it is passing to the touch command; if this ran successfully, then there should be some unusual filenames in its working directory now.
You can use a shell as your command and pass it the shell logic you would like:
command=/bin/sh -c "touch ~a.c && tail -f /dev/null"
Usually, this type of shell wrapper should be the interface provided and managed by the app and is what supervisord and others just know how to call with paths and options, i.e.:
command=myappswrapper.sh ~a.c
(where myappswrapper.sh is:)
#!/bin/sh
touch $1 && tail -f /dev/null
Here is a trick.
You use a shell script to do that and beyond that
[program:app]
command:sh /path/to/your/script.sh
It's can your script.sh
touch ~a.c
exec tail -f /dev/null
notice exec
I am using this command fine:
ssh user#ip 'bash -s' -- < /usr/local/nagios/libexec/check_ssh_mem.sh
I don't like the results of that script so want to use a perl script instead and use this:
ssh user#ip 'perl -s' -- < /usr/local/nagios/libexec/check_mem.pl
check_mem.pl v1.0 - Nagios Plugin
usage:
check_mem.pl -<f|u> -w <warnlevel> -c <critlevel>
options:
-f Check FREE memory
-u Check USED memory
-C Count OS caches as FREE memory
-w PERCENT Percent free/used when to warn
-c PERCENT Percent free/used when critical
As you can see, I get proper feedback from the script. I want to pass it the -f, -w and -c variables but get errors when trying to do that.
man perlrun says:
Upon startup, Perl looks for your program in one of the following places
...
3. Passed in implicitly via standard input. This works only if there are
no filename arguments--to pass arguments to a STDIN-read program you must
explicitly specify a "-" for the program name.
So, you can use this:
ssh user#ip 'perl - -f -u -C' -- < /usr/local/nagios/libexec/check_mem.pl
The arguments after the - are passed to the script you are running.
You don't need the -s argument - I assume you copied that from your original bash implementation, but -s has a different meaning for perl.
If I have a basic .sh file containing the following script code:
#!/bin/sh
rm -rf "MyFolder"
How do I make this running script file display results to the terminal that will indicate if the directory removal was successful?
You don't really need to make it say it was successful. You could have it say something only on error ✖, and then silence means success ✔.
That's how the Unix philosophy works:
The rule of silence, also referred to as the silence is golden rule, is an important part of the Unix philosophy that states that when a program has nothing surprising, interesting or useful to say, it should say nothing. It means that well-behaved programs should treat their users' attention and concentration as being valuable and thus perform their tasks as unobtrusively as possible. That is, silence in itself is a virtue. http://www.linfo.org/rule_of_silence.html
That's the way rm itself behaves.
If you are asking about the general case, as suggested by your question's title, you can run your script with sh -x scriptname to see what it's doing. It's also quite common to write diagnostic output into the script itself, and control it with an option.
#!/bin/sh
verbose=false
case $1 in -v | --verbose )
verbose=true
shift ;;
esac
say () {
$verbose || return
echo "$0: $#" >&2
}
say "Removing $dir ..."
rm -rf "$dir" || say "Failed."
If you run this script without any options, it will run silently, like a well-behaved Unix utility should. If you run it with the -v option, it will print some diagnostics to standard error.
rm -rf "My Folder" && echo "Done" || echo "Error!"
You can read more on creating a sequence of pipelines in bash manual
In the bash (and other similar shells) the ? environment variable gives you the exit code of the last executed command. So you can do:
#!/bin/sh
rm -rf "My Folder"
echo $?
UPDATE
If once the rm command has been executed the directory doesn't exist (because it has been successfully removed or because it didn't exist when the command was executed) the script will print 0. If the directory exists (which will mean that the command has been unable to remove it) then the script will print an exit code other than 0. If I understand properly the question this is exactly the requested behavior. If it is not, please correct me.
The previous answers was wrong : rm don't exit with error code > 0 when the dir isn't present.
Instead, I recommend to use :
dir='/path/to/dir'
if [[ -d $dir ]]; then
rm -rf "$dir"
fi
If you want rm to return a status, remove -f flag.
Example on Linux Mint (the dir doesn't exists):
$ rm -rf /tmp/sdfghjklm
$ echo $?
0
$ rm -r /tmp/sdfghjklm
$ echo $?
1
Can sh itself check if a program exists or is in path?
I.e., not with the help of the "which" program.
I don't believe sh can directly. But perhaps something like:
which() {
save_IFS=$IFS
IFS=:
for d in $PATH; do
test -x $d/$1 && echo $d/$1
done
IFS=$save_IFS
}
and here's a nice variation that uses a subshell so that restoring IFS is not necessary:
which() (
IFS=:
for d in $PATH; do
test -x $d/$1 && echo $d/$1
done
)
Also, (in bash) if the command has been executed in the past and bash has already done the PATH search, you can see what it found with hash -t.
bash-3.2$ hash -t which
bash: hash: which: not found
bash-3.2$ which foo
bash-3.2$ hash -t which
/usr/bin/which
The utility command -v $CMD is apparently a portable option (in the sense of being part of POSIX); see also the very similar (though bash-specific) question, in particular this answer.