How to split strings in shellscript

rasa · 09-22-2009, 02:09 AM

Hi,

I am trying to write a shell script. The purpose of the script is to provide the list of open files in server.

For that i need to get the pid. Here i am using pidof java and storing it in a variable

Quote:

[root@server usr1]# value=`pidof java`
[root@server usr1]# echo $value
13713 13643 13642
[root@server usr1]#

Here the value is a single string separated with space.
for executing ls -l /proc/procid/fd i need the process id value.

How i will get this.

Regards
Rasa.

acid_kewpie · 09-22-2009, 02:22 AM

for pid in $(pidof java)
do
something $pid
done

don't use backticks in scripting, use $(...) notation instead.

lutusp · 09-22-2009, 02:39 AM

Quote:

Originally Posted by rasa

Hi,

I am trying to write a shell script. The purpose of the script is to provide the list of open files in server.

For that i need to get the pid. Here i am using pidof java and storing it in a variable

Here the value is a single string separated with space.
for executing ls -l /proc/procid/fd i need the process id value.

How i will get this.

Regards
Rasa.

I assume you want the PIDs to be separated. Try this:

Code:

array=($(pidof java))

echo ${array[0]}

echo ${array[1]}

etc..

rasa · 09-23-2009, 12:09 AM

Quote:

Originally Posted by lutusp

I assume you want the PIDs to be separated. Try this:

Code:

array=($(pidof java))

echo ${array[0]}

echo ${array[1]}

etc..

Thanks very much for your replies.

I did it the following way.

Code:

PROCESS_ID=`pidof java`
echo "process id" $PROCESS_ID
VALUE1=`echo $PROCESS_ID | awk '{print $1}'`
VALUE2=`echo $PROCESS_ID | awk '{print $2}'`
VALUE3=`echo $PROCESS_ID | awk '{print $3}'`

slakmagik · 09-23-2009, 12:53 AM

What if there are two or four PIDs? acid_kewpie's method lets you iterate over however many there are and lutusp's can be modified to do that by iterating over the members of the array. But if it's constant, it's constant. Even so, those are probably more efficient than invoking multiple instances of awk. Even if you were going to do it your way, 'cut'ing on space delimiters would be more efficient.

And you're still using backticks.

acid_kewpie · 09-23-2009, 02:33 AM

Quote:

Originally Posted by rasa

Thanks very much for your replies.

I did it the following way.

Code:

PROCESS_ID=`pidof java`
echo "process id" $PROCESS_ID
VALUE1=`echo $PROCESS_ID | awk '{print $1}'`
VALUE2=`echo $PROCESS_ID | awk '{print $2}'`
VALUE3=`echo $PROCESS_ID | awk '{print $3}'`

Hmm, rather you than me, a number of much better solutions have already been posted, each with uses in slightly different ways. Seems illogical to me to assign three equivalent bits of data to three differently named variables. Arbitrary and overly rigid at best. Either loop through them implictly, or use an array for longer storage. Again, backticks are long obsolete, use $(...) instead.

mrrangerman · 09-23-2009, 06:07 AM

Quote:

acid_kewpie

for pid in $(pidof java)
do
something $pid
done

don't use backticks in scripting, use $(...) notation instead.

I'm rather new to scripting but I do know that both backticks and $(...) notation are legal forms of command substitution, so could you please explain why he shouldn't use backticks?

Thanks

i92guboj · 09-23-2009, 09:36 AM

I'd really use the looping or array approaches, jave tends to spawn threads all around after all, so just checking for one pid is misleading.

About `...` vs $(...), two things:

clarity: remember, you only have to write it once, it's not like in command line where `...` saves some typing... and it's much better readable
it can be nested, allowing you to do funny things like "echo $($(which ls) /etc)" -just a random example with no purpose, which can't be done with `...`

On the contrary, I am not sure how other shells deal with that, though. I think that this is a bashism and it's not compatible with the original sh, so if that's a concern to you, double check it, my memory is blurry.

acid_kewpie · 09-23-2009, 12:51 PM

what he said! To be honest I can't provide anything more formal, but backticks were "officially" deprecated over a decade ago now AFAIK.

slakmagik · 09-23-2009, 02:44 PM

Quote:

Originally Posted by i92guboj

On the contrary, I am not sure how other shells deal with that, though. I think that this is a bashism and it's not compatible with the original sh, so if that's a concern to you, double check it, my memory is blurry.

I'm almost positive it's not compatible with v7 sh but it is POSIX and ash has no problems with it. So I'd say it's not ultimately portable in the historical sense, but is portable in a current context.

unSpawn · 09-23-2009, 03:42 PM

Quote:

Originally Posted by rasa

I am trying to write a shell script. The purpose of the script is to provide the list of open files in server. For that i need to get the pid. Here i am using pidof java

Is there really a need to mess with 'ls' or arrays to get fds?:

Code:

pgrep -f java | xargs -iX /usr/sbin/lsof -P -w -n -p 'X' -a -d1-255

rasa · 09-24-2009, 08:45 AM

Quote:

Originally Posted by unSpawn

Is there really a need to mess with 'ls' or arrays to get fds?:

Code:

pgrep -f java | xargs -iX /usr/sbin/lsof -P -w -n -p 'X' -a -d1-255

Yes this is working fine. But what is the issue with the script which i have provided. Actually i have given that to my client. I am a java programmer and i don't know shell scripting much. I made it by referring some tutorial.

Regards
Rasa.

catkin · 09-24-2009, 09:08 AM

Quote:

Originally Posted by rasa

Yes this is working fine. But what is the issue with the script which i have provided.

Nothing, in the sense that it works, but it is unnecessarily complex and obscure so difficult to maintain and will call your competence into question if your client does not appreciate that you did you best in unknown territory and cannot be blamed for wielding a scalpel like a battle axe.

unSpawn's solution, on the other hand, is elegantly minimal and uses the power of the available tools.

acid_kewpie · 09-24-2009, 10:46 AM

Quote:

Originally Posted by unSpawn

Is there really a need to mess with 'ls' or arrays to get fds?:

Code:

pgrep -f java | xargs -iX /usr/sbin/lsof -P -w -n -p 'X' -a -d1-255

you're bloody good at this stuff. The things I learn from you never stop.