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1.4. Sample SystemTap scripts

Following are some example scripts that illustrate the basic operation of SystemTap. For more examples, see the examples/small_demos/ directory in the source directory, the SystemTap wiki at http://sourceware.org/systemtap/wiki/HomePage, or the SystemTap War Stories at http://sourceware.org/systemtap/wiki/WarStories page.

1.4.1. Basic SystemTap syntax and control structures

The following code examples demonstrate SystemTap syntax and control structures.

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global odds, evens

probe begin {
# "no" and "ne" are local integers
for (i = 0; i < 10; i++) {
if (i % 2) odds [no++] = i
else evens [ne++] = i
}

delete odds[2]
delete evens[3]
exit()
}

probe end {
foreach (x+ in odds)
printf ("odds[%d] = %d", x, odds[x])

foreach (x in evens-)
printf ("evens[%d] = %d", x, evens[x])
}

global odds, evens

probe begin {
# "no" and "ne" are local integers
for (i = 0; i < 10; i++) {
if (i % 2) odds [no++] = i
else evens [ne++] = i
}

delete odds[2]
delete evens[3]
exit()
}

probe end {
foreach (x+ in odds)
printf ("odds[%d] = %d", x, odds[x])

foreach (x in evens-)
printf ("evens[%d] = %d", x, evens[x])
}

This prints:

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odds[0] = 1
odds[1] = 3
odds[3] = 7
odds[4] = 9
evens[4] = 8
evens[2] = 4
evens[1] = 2
evens[0] = 0

odds[0] = 1
odds[1] = 3
odds[3] = 7
odds[4] = 9
evens[4] = 8
evens[2] = 4
evens[1] = 2
evens[0] = 0

Note that all variable types are inferred, and that all locals and globals are initialized.

1.4.2. Primes between 0 and 49

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function isprime (x) {
if (x < 2) return 0
for (i = 2; i < x; i++) {
if (x % i == 0) return 0
if (i * i > x) break
}
return 1
}

probe begin {
for (i = 0; i < 50; i++)
if (isprime (i)) printf("%d\n", i)
exit()
}

function isprime (x) {
if (x < 2) return 0
for (i = 2; i < x; i++) {
if (x % i == 0) return 0
if (i * i > x) break
}
return 1
}

probe begin {
for (i = 0; i < 50; i++)
if (isprime (i)) printf("%d\n", i)
exit()
}

This prints:

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1.4.3. Recursive functions

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function fibonacci(i) {
if (i < 1) error ("bad number")
if (i == 1) return 1
if (i == 2) return 2
return fibonacci (i-1) + fibonacci (i-2)
}

probe begin {
printf ("11th fibonacci number: %d", fibonacci (11))
exit ()
}

function fibonacci(i) {
if (i < 1) error ("bad number")
if (i == 1) return 1
if (i == 2) return 2
return fibonacci (i-1) + fibonacci (i-2)
}

probe begin {
printf ("11th fibonacci number: %d", fibonacci (11))
exit ()
}

This prints:

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11th fibonacci number: 118

11th fibonacci number: 118

Any larger number input to the function may exceed the MAXACTION or MAXNESTING limits, which will be caught at run time and result in an error. For more about limits see Section Section 1.6, “Safety and security”.

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