3.5.6. Using Arrays in Conditional Statements

⁠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:

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Example 3.19. vfsreads-print-if-1kb.stp

global readsprobe 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 3.19, “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:

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Example 3.20. vfsreads-stop-on-stapio2.stp

global readsprobe 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.