3.5.6. Using Arrays in Conditional Statements
You can also use associative arrays in
if statements. This is useful if you want to execute a subroutine once a value in the array matches a certain condition. Consider the following example:
Example 3.17. vfsreads-print-if-1kb.stp
global reads
probe vfs.read
{
reads[execname()] ++
}
probe timer.s(3)
{
printf("=======\n")
foreach (count in reads-)
if (reads[count] >= 1024)
printf("%s : %dkB \n", count, reads[count]/1024)
else
printf("%s : %dB \n", count, reads[count])
}
Every three seconds, Example 3.17, “vfsreads-print-if-1kb.stp” prints out a list of all processes, along with how many times each process performed a VFS read. If the associated value of a process name is equal or greater than 1024, the
if statement in the script converts and prints it out in kB.
Testing for Membership
You can also test whether a specific unique key is a member of an array. Further, membership in an array can be used in if statements, as in:
if([index_expression] in array_name) statement
To illustrate this, consider the following example:
Example 3.18. vfsreads-stop-on-stapio2.stp
global reads
probe vfs.read
{
reads[execname()] ++
}
probe timer.s(3)
{
printf("=======\n")
foreach (count in reads+)
printf("%s : %d \n", count, reads[count])
if(["stapio"] in reads) {
printf("stapio read detected, exiting\n")
exit()
}
}
The
if(["stapio"] in reads) statement instructs the script to print stapio read detected, exiting once the unique key stapio is added to the array reads.
