Room for Elad and terdon

Elad

10:24

@terdon hi

terdon

@Elad Hi

So, why would you need to replace anything?

The $0 is the name of the script. That's a special shell variable and, no matter what your script, $0 will always be the path to it.

Elad

@terdon but there is no $0 in the syntax. it's "${0##*/}"

terdon

@Elad Sure there is. Right before the first #

Elad

@Elad I don't see $0 I see ${0

@terdon I don't see $0 I see ${0

terdon

@Elad Yes, $var and ${var} are the same thing.

In this case, we are using the shells text replacement capabilities to change the variable.

Elad

10:27

@terdon so it should be ${abcd.sh} ?

terdon

No, it should be exactly as it is: ${0##*/}

The general format is ${var##pattern} which will remove pattern from the beginning of the string.

For example:

Elad

@terdon ${abcd.sh##*/}

terdon

@Elad No, ${0##*/}

Here, look at this example:

Elad

@terdon can you give an example with an actual file name? I don't understand the syntax

terdon

$ var="foobar"
$ echo ${var}
foobar
$ echo ${var##foo}
bar

@Elad The file name is automatically saved as $0 in your script. You don't need to change anything at all.

Elad

10:29

@terdon so jsut run it as it is?

terdon

In the example above, the variable $var has the value foobar. If I then echo ${var##foo} (which means "the value of the variable $var after removing the string foo from the beginning), I get bar

@Elad Yep. The $0 is a special variable that always holds the name of the current script. Well, the path to the current script anyway. Here, consider this script:

#!/bin/bash
echo "\$0 is $0"
echo "\${0##*/} is ${0##*/}"

I have saved it as foo.sh:

Elad

@terdon Ok. Ill test it now

terdon

$ foo.sh
$0 is /home/terdon/scripts/foo.sh
${0##*/} is foo.sh

Now, I rename it to bar.sh:

Elad

@terdon just for my kownledge what -gt 1 means?

terdon

cp ~/scripts/foo.sh ~/scripts/bar.sh

And run it again:

$ bar.sh
$0 is /home/terdon/scripts/bar.sh
${0##*/} is bar.sh

See? Same script, same code, but the value of $0 changes.

@Elad "greater than". It's a numerical operator. You have -gt, -ge (greater than or equal) and similarly -lt ("less than"), -le (less than or equal) and -eq (equal)

Elad

10:35

@terdon OK. the file name is ok but the script doesn't work. It doesn't recognize that another instance is running. I opened two consoles and ran it

terdon

@Elad don't look at FreeBSD manuals, there will often be differences if you're using Linux.

@Elad OK, can you show me the exact code you ran?

Elad

@terdon Copy paste from your code. didn't change anything. Just after ur code I run my SQL comand... It should do EXIT if it found another instance running

terdon

@Elad Why would an SQL command exit? Was it the exact same shell script running twice?

Look, the trick (and what you asked for in your question) is to make a shell script exit if another copy of the same shell script is running. If you go and run the SQL command without the script, it won't work.

Elad

@terdon The SQL is the command my script suppos to run. I want it to run it only if there is no other instance of the script running. What happens after ur IF is just the regular operation of my script

terdon

@Elad The script won't stop the same SQL command from running, it will stop another copy of the script from running.

If you instead run the SQL command manually, of course that will run.

Elad

10:38

@terdon You missundestod. My script is: if [ $(pgrep -c "${0##*/}") -gt 1 ]; then
echo "Another instance of the script is running. Aborting."
exit
fi SQL COMMAND.

terdon

OK. And you ran two of those?

Elad

@terdon The SQL should happen when the IF is false. IF it's true the exit after echo should stop the script.

terdon

Yes

Elad

@terdon I opened two consoles.. ran it once.. and while it's running I ran it again.

terdon

How long does the SQL command take? Are you sure it was still running when you launched the second instance?

Elad

10:40

@terdon I'm sure because I see on colsole when it's done...

terdon

OK, hang on, let's take this to another room so we don't hijack this one. Gimme a sec.

Elad

@terdon You can test it with sleep... instad of my SQL command you can use sleep for 5 minutes...

terdon

@Elad I know. I already have and it works.

← 54 messages moved from Ask Ubuntu General Room

OK. So, can you try this please:

#!/bin/bash
if [ $(pgrep -c "${0##*/}") -gt 1 ]; then
     echo "Another instance of the script is running. Aborting."
     exit
fi
sleep 10

Elad

yes just a second

terdon

Then run it twice and tell me what happens. On my system:

$ foo.sh &
[1] 19072
$ foo.sh
Another instance of the script is running. Aborting.

Elad

10:45

both run at the same time

im using ubuntu 12 could this be related?

terdon

No. There's something else going on. OK, can you run this please:

#!/bin/bash
if [ $(pgrep -c "${0##*/}") -gt 1 ]; then
     echo "Another instance of the script is running. Aborting."
     exit
fi
else
    echo "PP: ${0##*/} : $(pgrep -c ${0##*/})"
fi

Elad

I should note that the pgrep always give me 0

terdon

@Elad Yes, that's what I expect.

Oh hang on.

You're running the script as bash scriptName.sh right?

Elad

it doesn't matter if another one is running pgrep always give 0

terdon

And not just scriptName.sh?

Elad

10:47

no bash... just the scriptname.sh

terdon

OK, can you run the one above then?

I need to see the output of the PP line

I just made a small correction, that should be PP: ${0##*/} and not PP: $${0##*/}

Argh.

Sorry, I'm being dense

Syntax error. Give me a sec

Elad

yes syntax error

terdon

OK, please run this:

#!/bin/bash
printf "0: %s\n" "$0"
ps aux | grep "$0"

Elad

I removed also the fi

I got 0 in the result

terdon

Yes, please run the one above

Elad

10:52

remove the last and run this?

terdon

Yes

That will show me i) the value of $0 and ii) what name the script runs under. It should help us figure out why it's not found by pgrep

Elad

sec

root 20722 0.0 0.0 9360 620 pts/0 S+ 13:52 0:00 grep /scripts/syncpoallocation

terdon

I need all the output.

Elad

this is the output

terdon

???

You should see something like this:

$ foo.sh
0: /home/terdon/scripts/foo.sh
terdon   22749  0.0  0.0  14948  2796 pts/6    S+   13:50   0:00 /bin/sh /home/terdon/scripts/foo.sh
terdon   22751  0.0  0.0  12020  2244 pts/6    R+   13:50   0:00 grep /home/terdon/scripts/foo.sh

Elad

10:55

this is what it give.. it doesn't seem to be running

terdon

You are only showing me the last line of output.

Elad

ok now it shows more:

0: /scripts/syncpoallocation
root 21623 0.0 0.0 4404 612 ? Ss 13:56 0:00 /bin/sh -c /scripts/syncpoallocation 1>/dev/null 2>/dev/null
root 21624 0.0 0.0 4404 612 ? S 13:56 0:00 /bin/sh /scripts/syncpoallocation
root 21640 0.0 0.0 9360 620 pts/0 S+ 13:56 0:00 grep /scripts/syncpoallocation

"${0##*/}" is ok. it shows what you said. $0 is also ok

I tried to re run it.. now also just one line: 0: /scripts/syncpoallocation
root 21672 0.0 0.0 9360 616 pts/0 S+ 13:57 0:00 grep /scripts/syncpoallocation

terdon

HOw are you running it? What exact command are you using?

Elad

/scripts/syncpoallocation

terdon

And you changed the #!/bin/bash I told you to #/bin/sh

Even so, it should work.

But please run it again exactly as I showed it so with #!/bin/bash as the first line and not #!/bin/sh

Elad

11:01

in both cases it doesn't work :(

sec

This? #/bin/sh printf "0: %s\n" "$0"
ps aux | grep "$0"

terdon

@Elad No. You changed it to sh instead of bash again

#!/bin/bash
printf "0: %s\n" "$0"
ps aux | grep "$0"

Elad

it's not running

this is what i get:

terdon

?

Elad

any ideas?

terdon

@Elad Depends, what do you get? You haven't shown me.

Elad

11:10

I did...

0: /scripts/syncpoallocation
root 23678 0.0 0.0 9360 620 pts/0 S+ 14:04 0:00 grep /scripts/syncpoallocation

This is the returned value. The script is not ruuning with this command

terdon

If it isn't running, how do you get output?

Oh hang on. Please tell me you are not using a Windows machine to connect to Ubuntu

Elad

No, Ubuntu directly

terdon

And you're not editing anything on Windows?

Elad

No windows involved.

Say I want to print to colnsole the number of scrips running (with this name) something like: print number, sleep 1000 If i'll run it 3 time I should see 0 then 1 then 2 right?

terdon

No. You should never see 0.

That's the problem.

OK, one more try. Run this and show me the output:

#!/bin/bash
printf "0: %s\nCut: %s\n" "$0" "${0##*/}"
ps aux | grep "$0"
echo "P1: $(pgrep ${0##*/})"
echo "P2: $(pgrep -f  ${0##*/})"

Elad

11:17

sec

0: /scripts/syncpoallocation.sh
Cut: syncpoallocation.sh
root 25884 0.0 0.0 9360 616 pts/1 S+ 14:17 0:00 grep /scripts/syncpoallocation.sh
P1:
P2:

terdon

OK, no, that's just impossible :)

Makes no sense. One more try:

#!/bin/bash
printf "0: %s\nCut: %s\n" "$0" "${0##*/}"
ps aux | grep "syncpoallocation"

Elad

When I do:

#!/bin/bash
printf "0: %s\nCut: %s\n" "$0" "${0##*/}"
echo $0
echo ${0##*/}
ps aux | grep "$0"
echo "P1: $(pgrep ${0##*/})"
echo "P2: $(pgrep -f ${0##*/})"

I get:

0: /scripts/syncpoallocation.sh
Cut: syncpoallocation.sh
/scripts/syncpoallocation.sh
syncpoallocation.sh
root 26169 0.0 0.0 9360 620 pts/1 S+ 14:19 0:00 grep /scripts/syncpoallocation.sh
P1:
P2:

terdon

@Elad Yes, and that makes no sense at all. The ps aux | grep $0 should have two results, not one. Which is why I asked you to run it again but searching explicitly for syncpoallocation

Ah, no, even better. Try this:

#!/bin/bash
ps aux | grep "$$"

Elad

I think I know what may cause it

terdon

@Elad Oh?

Elad

11:23

when the script is running.. I don't see it on ps aux it's like it doesn't exists

terdon

I know. That's what's so weird.

Try what I gave you above. That will search for $$ (the script's process id).

#!/bin/bash
ps aux | grep "$$"

@Elad?

Elad

sec

root 28772 0.0 0.0 12320 1380 pts/0 S+ 14:29 0:00 /bin/bash /scripts/syncpoallocation.sh
root 28774 0.0 0.0 9360 616 pts/0 S+ 14:29 0:00 grep 28772

terdon

Argh! That makes no sense! There's the script, running normally, so why isn't it shown when we grep for it?

Elad

Could this be a bug in the operating system?

terdon

No

Elad

11:32

my ubuntu is old (12)

terdon

This hasn't changed since long before Linux was even created.

Could there be some sort of strange character in the script's name? Try this:

#!/bin/bash
ps aux | grep "$$" | grep -v grep | od -c

Elad

it's regular english letters...

terdon

Te output will be several weird looking lines. Just paste them here

@Elad I know. I'm clutching at straws here. There might be a non-printing character in there and this should show it.

Elad

root@pg-production01:~# /scripts/syncpoallocation.sh
0000000 r o o t 2 9 7 7 4
0000020 0 . 0 0 . 0 2 3 3 1 2
0000040 3 5 4 8 p t s / 0 S
0000060 + 1 4 : 3 4 0 : 0 0
0000100 - b a s h \n
0000107

terdon

OK.

So it looks like it's only showing the script as "bash" and not "bash scriptName.sh"

Elad

11:37

what is that means?

terdon

@Elad Nothing, it's a trick that will show you each character. Note the \n at the end, that's a newline which is normally invisible. The point is that the script name isn't included, it only shows bash for some reason.

And that's why it doesn't work when we search for the script name

Elad

How do I solve it?

terdon

OK, forget it then, use the second approach with the lock file:

Add this to the beginning of the real script:

if [ -e "/tmp/i.am.running" ]; then
    echo "Another instance of the script is running. Aborting."
    exit
fi
else
    touch  "/tmp/i.am.running"
fi

(you might want to change i.am.running to syncpoallocation.running or something. But it's up to you. )

Then, add this to the end of the script:

Elad

I prefer not to do it with file locks.. :(

terdon

Yeah. I can understand that.

But if your system is behaving in this weird way, I don't know how to get around it.

Elad

11:40

I think i'll wait till we upgrade to ubuntu 14 maybe it will be resolved on itself

terdon

I doubt it. It's really odd.

What in the world are you doing on Ubuntu 12 anyway?

Oh, and are you really doing this logged in as root on a production system?

If I were your boss, I'd have probably fired you now.

You never, ever test commands given by random strangers on the internet as root and NEVER as root on a production system!

Elad

our last upgrade was at 2014. Since ubuntu also upgrades packages like python etc.. we can not "just upgrade it".... it effects everything in our system... it takes about 4-5 months to check everything works with the new OS

terdon

Seriously. Don't ever do that again.

I might have given you a command that would break the system. Either because I'm malicious or just by mistake. Never test things as root.

(sorry, rant over, I couldn't help myself)

Elad

it's not our root production.. it's just called this way :) it's a server which used to be production but not used anymore

terdon

Ah, phew

I feel better now :)

Elad

11:43

lol... it took me a while to respond to use because i double checked your instructions.. even when it's test server i double check :)

terdon

Good! You wouldn't believe how many ~~idiots~~ users break their systems this way.

Let's test one more thing. Run these commands and tell me their output:

file /bin/bash
/bin/bash --version
type -a bash

Elad

sec

4.2.24 (1)-release

terdon

And file /bin/bash tells you it's an ELF executable, right?

Elad

11:59

I have to go to a meeting so I won't be able to contine... Thank you so much for your time... I'll try to look for more solutions :)

terdon

@Elad You're welcome and sorry I couldn't be more help. I suggest you ask a new question but on Unix & Linux (your version of Ubuntu is off topic here). Give one of the really simple scripts we tried here and the output of ps and ask why ps only shows bash and not the name of the script.

If we can figure that out, the rest should be easy.

Elad

will do. thank you :)

terdon

@Elad Let me know if you do, please. I'm curious now :)

Transcript for

Room for Elad and terdon