UNIX for Advanced & Expert Users

please suggest me a way to write c program that takes pattern of the process and returns true or false


my case is i need to keep track of dhcpcd

dhcpcd -d eth1

so i tried popen("ps -ef | grep dhcpcd | grep eth1 | wc -l", "r");

but pipe is storing 1 or 2 when not running
and 2 or 3 when running.

please suggest a good way to do this

is there any api in linux for the same instead of doing file operations.

When the process is not running, it will return the value 2
1. popen invokes the shell to execute the given command ( that sh command also will have the given pattern)
2. grep command with the given patter

and when the process is running it will return the value >2

So one of the way to find this is,

you have to convert the data reading from the pipe to integer through atoi()
and subtract 2. Then if the result is 0 - the process is not running.
if the result is > 0 the process is running.

Thanks for reply skmdu

some times when dhcpcd is not running it is returning 1 mostly and 2 rarely
and when dhcpcd is running it is returning 2 mostly and 3 some times
problem is both cases are having 2 as output some time.

not understanding the reason why

generally it would be like

if ps -ef | grep dhcpcd
it would give
1) if dhcpcd is running that entry and our command entry (grep dhcpcd)
so the number of lines should be 2
2) if not running just (grep dhcpcd) entry , so the number of lines should be 1

any reason for returning 3 when running and returning 2 when not running ?

You just remove wc -l from the command and see the result of grep..

Then you will get some understanding when it is returning 2 for both the case?

Code:

ps -eo pid,ppid,cmd | grep <process_name> | grep -v grep

Replace the process_name and u can get the result as having pid in the first column, ppid as the second column and command name as the third column.

The first line probably has the ppid 1. Perhaps, if u see a second line, its ppid will be the first line's pid which means it is started from that process.

what grep -v grep indicates ?

Works at least under Solaris and Gnu/Linux:

Code:

pgrep -f "dhcpd.*eth1"