Shell Programming and Scripting

Hello.
I would like to do this :

A_VAR_FLAG = "ABCD" +------------+...................................+---------+
...............................|.................|...................................|.............|
...............................| ................|...................................|.............|
...............................| ................|...................................|.............|
A_VAR_FLAG = ""....... + ................+------------------------+............. +-------------------------------

cron call

a script . . . . . . . the script after

which set . . . . . . 5sec reset

A_VAR_FLAG . . . . A_VAR_FLAG

to "ABCD" . . . . . . to ""

-
-
A_VAR_FLAG must be visible to rsyslog ( service started during boot ).

rsyslog.conf contains this filtre :

Code:

 if $msg  contains getenv('A_VAR_FLAG') then

So depending the value of A_VAR_FLAG, $msg is kept or thrown away.

Any help is welcome.

You cannot change the environment of a procees that is running except from within. Have the parent export A_VAR_FLAG before calling rsyslog.

Hello.
When rsyslog starts during boot ( or when it is restarted by hand ) , it read a config file which indicate some filter to use. And the filter syntax permit the use of environment variable as in my example "getenv('A_VAR_FLAG')" .

So do you mean that even if the global variable A_VAR_FLAG is created before rsyslog start, I have no way to change the point of view of rsyslog about the value of the variable A_VAR_FLAG ?

Can you not:

1. create two environment variables A_VAR_FLAG='ABCD' and B_VAR_FLAG="" in the process when it starts. This part has nothing to do with config files, just the cron (or services startup ) script needs to have two lines:

Code:

export A_VAR_FLAG="ABCD"
export B_VAR_FLAG=""

2. have two separate rsyslogd.conf (or whatever name you use) files, one which specifies

Code:

getenv('A_VAR_FLAGS')

the other is identical except for

Code:

getenv('B_VAR_FLAGS')

3. create 2 files, something_A and something_B (you make up names).
something_A is the original startup. At startup:

Code:

cp something_A rsyslogd.conf
# code to start rsyslogd goes here
sleep 5
cp something_B rsyslogd.conf
pid=$(pgrep rsyslogd)
kill -HUP $pid # force rsyslogd to reread the config files

Basically I do not understand your requirement. At all. If you need to turn this filter on and off there are other more conventional ways to do it. Like stopping rsyslogd.

( I do not know the services command for your version but it amounts to this)

Code:

rsyslogd -f fileA
sleep 5
kill $(prgrep rsyslogd)
rsyslogd -f fileB

DGPickett is correct you cannot change a running process environment variables unless the process already has a direct means to change it. Specifically an IPC tool. Instead, you have to force the process to use another already existing variable, using a round about method. Or stop the process completely and recreate it with the right environment in the first place.

One easy IPC is to fetch the value from a file each loop A_VAR_FLAGS=$(<file), or source (.) a small config file like a short .profile that can be modiified, so any proc can rewrite the file and change the next pass.

Stopping rsyslog is not the good way ( risk of loosing messages ).
I Know that I can use a file ( I use that often ) but rsyslog give function only to read environment variable.

You can modify rsyslog to store this flag in a mmap()'d file, so you can modify that file on the fly -- no overhead, no interruptions, 1 additional page in working set.