There are a number of system or built-in variables defined by awk. Awk has two types of system variables. The first type defines values whose default can be changed, such as the default field and record separators. The second type defines values that can be used in reports or processing, such as the number of fields found in the current record, the count of the current record, and others. These are updated by awk; for example, the current record number and input file name. There are a set of default values that affect the recognition of records and fields on input and their display on output. The system variable defines the field separator. By default, its value is a single space, which tells awk that any number of spaces and/or tabs separate fields. can also be set to any single character, or to a regular expression. Earlier, we changed the field separator to a comma in order to read a list of names and addresses. , which is a space by default. We'll see an example of redefining to be the number of fields for the current input record. Changing the value of actually has side effects. The interactions that occur when are changed is a murky area, particularly when is decreased. Increasing it creates new (empty) fields, and rebuilds , with the fields
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Topics of Interest
This section summarizes how awk processes input records and describes the various syntactic elements that make up an awk program. Each line of input is split into fields. By default, the field...
Awk makes the assumption that its input is structured and not just an endless string of characters. In the simplest case, it takes each input line as a record and each word, separated by spaces or...
Awk provides two system variables that are arrays: An array of command-line arguments, excluding the script itself and any options specified with the invocation of awk. The number of elements in this...
The built-in string functions are much more significant and interesting than the numeric functions. Because awk is essentially designed as a string-processing language, a lot of its power derives from...
Other Statements That Affect Flow Control System Variables That Are Arrays This chapter covers some fundamental programming constructs. It covers all the control statements in the awk programming...