Associative Arrays; Examples; Types Of Values; Array Capacity - Red Hat ENTERPRISE LINUX 5.4 - SYSTEMTAP LANGUAGE Reference Manual

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Chapter 7.

Associative arrays

Associative arrays are implemented as hash tables with a maximum size set at startup. Associative

arrays are too large to be created dynamically for individual probe handler runs, so they must be

declared as global. The basic operations for arrays are setting and looking up elements. These

operations are expressed in awk syntax: the array name followed by an opening bracket ([), a comma-

separated list of up to five index index expressions, and a closing bracket (]). Each index expression

may be a string or a number, as long as it is consistently typed throughout the script.

# Increment the named array slot:

foo [4,"hello"] ++

# Update a statistic:

processusage [uid(),execname()] ++

# Set a timestamp reference point:

times [tid()] = get_cycles()

# Compute a timestamp delta:

delta = get_cycles() - times [tid()]

Array elements may be set to a number or a string. The type must be consistent throughout the use

of the array. The first assignment to the array defines the type of the elements. Unset array elements

may be fetched and return a null value (zero or empty string) as appropriate, but they are not seen by

a membership test.

Array sizes can be specified explicitly or allowed to default to the maximum size as defined

Section 1.6, "Safety and security"

by MAXMAPENTRIES. See Section

for details on changing

MAXMAPENTRIES.

You can explicitly specify the size of an array as follows:

global ARRAY[<size>]

If you do not specify the size parameter, then the array is created to hold MAXMAPENTRIES number

of elements

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