11.2 Command-Line Syntax

The syntax for invoking awk has two forms:

awk  [options
]  'script
'  var
=value  file(s)

awk  [options
]  -f scriptfile  var
=value  file(s)

You can specify a script directly on the command line, or you can store a script in a scriptfile and specify it with -f . nawk allows multiple -f scripts. Variables can be assigned a value on the command line. The value can be a literal, a shell variable ($ name ), or a command substitution (` cmd ` ), but the value is available only after the BEGIN statement is executed.

awk operates on one or more files . If none are specified (or if - is specified), awk reads from the standard input.

The recognized options are:

-F fs

Set the field separator to fs . This is the same as setting the system variable FS . Original awk allows the field separator to be only a single character. nawk allows fs to be a regular expression. Each input line, or record, is divided into fields by whitespace (blanks or tabs) or by some other user-definable record separator. Fields are referred to by the variables $1 , $2 ,..., $ n . $0 refers to the entire record.

-v var = value

Assign a value to variable var . This allows assignment before the script begins execution (available in nawk only).

To print the first three (colon-separated) fields of each record on separate lines:

awk -F: '{ print $1; print $2; print $3 }' /etc/passwd

More examples are shown in Section 11.3.3, "Simple Pattern-Procedure Examples" .