---
name: "stapex"
section: "5"
platform: "linux"
package: "systemtap"
version: "0.0.20080705-1+lenny1"
release: "Debian 5.0 (Lenny)"
platforms: ["linux"]
url: "https://new.carta.tech/stapex/5"
---

# stapex(5)

systemtap examples

## NAME

stapex - systemtap examples

## LANGUAGE BASICS

These examples give a feel for basic systemtap syntax and control structures.

```
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] = %d0, x, odds[x])
  }
  foreach (x in evens-) {
    printf ("evens[%d] = %d0, x, evens[x])
  }
}
```

This prints:\

```
odds[1] = 1
odds[3] = 5
odds[4] = 7
odds[5] = 9
evens[5] = 8
evens[4] = 6
evens[2] = 2
evens[1] = 0
```

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

This script prints the primes between 0 and 49.\

```
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("%d0, i)
  exit()
}
```

This script demonstrates recursive functions.\

```
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: %d0, fibonacci (11))
  exit ()
}
```

Any larger number may exceed the MAXACTION or MAXNESTING limits, and result in an error.

## PROBING

To trace entry and exit from a function, use a pair of probes:\

```
probe kernel.function("sys_mkdir") { println ("enter") }
probe kernel.function("sys_mkdir").return { println ("exit") }
```

To list the probeable functions in the kernel, use the listings mode.\

```
% stap -l 'kernel.function("*")'
```

## SEE ALSO

**/usr/share/doc/systemtap/examples** [*stap*(1)](/stap/1.md) [*stapprobes*(5)](/stapprobes/5.md) [*stapfuncs*(5)](/stapfuncs/5.md)