z/OS V1R9.0 UNIX System Services Command ... - Christian Grothoff

Table 2. The Order of Operations for awk (continued)
Operators Order of operations
A || B Logical OR
A ? B : C Conditional expression
V=B V+=B V-=B V*=B V/=B V%=B V^=B Assignment
Notes:
1. A, B, C are any expression.
2. i is any expression yielding an integer.
3. V is any variable.
Command-line arguments
awk sets the built-in variable ARGC to the number of command-line arguments.
The built-in array ARGV has elements subscripted with digits from zero to ARGC−1,
giving command-line arguments in the order they appeared on the command line.
The ARGC count and the ARGV vector do not include command-line options
(beginning with -) or the program file (following –f). They do include the name of
the command itself, initialization statements of the form var=value, and the names
of input data files.
awk actually creates ARGC and ARGV before doing anything else. It then “walks
through” ARGV, processing the arguments. If an element of ARGV is an empty
string, awk skips it. If it contains an equals sign (=), awk interprets it as a variable
assignment. If it is a minus sign (−), awk immediately reads input from stdin until it
encounters the end of the file. Otherwise, awk treats the argument as a filename
and reads input from that file until it reaches the end of the file.
Note: awk runs the program by “walking through” ARGV in this way; thus, if the
program changes ARGV, awk can read different files and make different
assignments.
Input
awk divides input into records. A record separator character separates each record
from the next. The value of the built-in variable RS gives the current record
separator character; by default, it begins as the newline (\n). If you assign a
different character to RS, awk uses that as the record separator character from that
point on.
awk divides records into fields. A field separator string, given by the value of the
built-in variable FS, separates each field from the next. You can set a specific
separator string by assigning a value to FS, or by specifying the –F ere option on
the command line. You can assign a regular expression to FS. For example:
FS = "[,:$]"
says that commas, colons, or dollar signs can separate fields. As a special case,
assigning FS a string containing only a blank character sets the field separator to
white space. In this case, awk considers any sequence of contiguous space or tab
characters a single field separator. This is the default for FS. However, if you assign
FS a string containing any other character, that character designates the start of a
new field. For example, if we set FS=\t (the tab character),
texta \t textb \t \t \t textc
awk
Chapter 2. Shell command descriptions 37