Pass php variable to exec - php

Question

I need to get dimm info using ipmitool as follows:
exec("/usr/bin/ipmitool -I lan -H $spip -U root -P '$thepassword' sunoem cli 'show System/Memory/DIMMs/$a' | grep -i location", $dimm_loc, $ipmiretval);
$a is previously defined as:
$a=$dimm[$i]
The return value for the above exec command is 1. If I replace $a with its vaule, i.e
exec("/usr/bin/ipmitool -I lan -H $spip -U root -P '$thepassword' sunoem cli 'show System/Memory/DIMMs/D5' | grep -i location", $dimm_loc, $ipmiretval);
The exec command executes as expected. So it looks like $a cannot be used in the above example. How else can I pass the variable to the exec command?
Thanks!!

Answer 1

Run var_dump($a) and see what actualy it contains. Also dump the executed command as a string to see if command is formated properly.

Answer 2

One more tip. Instead of doing an exec("some very long command line"), put your command line in a variable, then both LOG and exec() the variable. For example:
$fmt="/usr/bin/ipmitool -I lan -H %s -U root -P '%s' sunoem cli 'show System/Memory/DIMMs/%s' | grep -i location";
$cmd=sprintf($fmt, $spip, $thepassword, $a);
exec($cmd, $dimm_loc, $ipmiretval);
syslog(LOG_DEBUG, "Running: $cmd");
if ($ipmiretval > 0) {
syslog(LOG_ERR, "exec FAILED: $cmd");
} else {
syslog(LOG_DEBUG, "exec: $cmd");
}