In the typical awk program, all input is read either
from the standard input (by default, this is the keyboard, but often it
is a pipe from another command) or from files whose names you specify
on the awk command line. If you specify input
files, awk reads them in order, processing all the
data from one before going on to the next. The name of the current
input file can be found in the built-in variable
the Section 6.5 in Chapter 6).
The input is read in units called records, and is processed by the rules of your program one record at a time. By default, each record is one line. Each record is automatically split into chunks called fields. This makes it more convenient for programs to work on the parts of a record.
On rare occasions, you may need to use the
getline command is valuable, both
because it can do explicit input from any number of files, and because
the files used with it do not have to be named on the
awk command line (see Section 3.8 later in this chapter).
The awk utility divides the input for your
awk program into records and fields.
awk keeps track of the number of records that have
been read from the current input file. This value is stored in a
built-in variable called
FNR. It is reset to zero
when a new file is started. Another built-in variable,
NR, is the total number of input records read so far from all datafiles. It starts at zero, but is never automatically ...