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

|
|
|
Files that you specify on the command line with the file argument provide the input
data for awk to manipulate. If you specify no files or you specify a dash (–) as a
file, awk reads data from standard input (stdin).
You can initialize variables on the command line using:
var=value
You can intersperse such initializations with the names of input files on the
command line. awk processes initializations and input files in the order they appear
on the command line. For example, the command:
awk -f progfile a=1 f1 f2 a=2 f3
sets a to 1 before reading input from f1 and sets a to 2 before reading input from f3.
Variable initializations that appear before the first file on the command line are
performed immediately after the BEGIN action. Initializations appearing after the
last file are performed immediately before the END action. For more information on
BEGIN and END, see Patterns.
The –v option lets you assign a value to a variable before the awk program begins
execution (that is, before the BEGIN action). For example, in:
awk -v v1=10 -f prog datafile
awk assigns the variable v1 its value before the BEGIN action of the program (but
after default assignments made to such built-in variables as FS and OFMT; these
built-in variables have special meaning to awk, as described later).
awk divides input into records. By default, newline characters separate records;
however, you can specify a different record separator if you want.
One at a time, and in order, awk compares each input record with the pattern of
every rule in the program. When a pattern matches, awk performs the action part of
the rule on that input record. Patterns and actions often refer to separate fields
within a record. By default, white space (usually blanks, newlines, or horizontal tab
characters) separates fields; however, you can specify a different field separator
string using the –F ere option).
You can omit the pattern or action part of an awk rule (but not both). If you omit
pattern, awk performs the action on every input record (that is, every record
matches). If you omit action, awk's default action is equivalent to: {print}.
awk considers everything after a # in a program line to be a comment. For
example:
# This is a comment
To continue program lines on the next line, add a backslash (\) to the end of the
line. Statement lines ending with a comma (,), double or-bars (||), or double
ampersands (&&) continue automatically on the next line.
Variables and expressions
There are three types of variables in awk: identifiers, fields, and array elements.
An identifier is a sequence of letters, digits, and underscores beginning with a letter
or an underscore. These characters must be from the POSIX portable character
set. (Data can come from other character sets.)
awk
Chapter 2. Shell command descriptions 33