6.1.3.2 Assigning Variables on the Command Line

Any awk variable can be set by including a variable assignment among the arguments on the command line when awk is invoked (see section Other Command-Line Arguments). Such an assignment has the following form:

variable=text

With it, a variable is set either at the beginning of the awk run or in between input files. When the assignment is preceded with the -v option, as in the following:

-v variable=text

the variable is set at the very beginning, even before the BEGIN rules execute. The -v option and its assignment must precede all the file name arguments, as well as the program text. (See section Command-Line Options for more information about the -v option.) Otherwise, the variable assignment is performed at a time determined by its position among the input file arguments—after the processing of the preceding input file argument. For example:

awk '{ print $n }' n=4 inventory-shipped n=2 mail-list

prints the value of field number n for all input records. Before the first file is read, the command line sets the variable n equal to four. This causes the fourth field to be printed in lines from inventory-shipped. After the first file has finished, but before the second file is started, n is set to two, so that the second field is printed in lines from mail-list:

$ awk '{ print $n }' n=4 inventory-shipped n=2 mail-list
-| 15
-| 24
…
-| 555-5553
-| 555-3412
…

Command-line arguments are made available for explicit examination by the awk program in the ARGV array (see section Using ARGC and ARGV). awk processes the values of command-line assignments for escape sequences (see section Escape Sequences). (d.c.)

Normally, variables assigned on the command line (with or without the -v option) are treated as strings. When such variables are used as numbers, awk’s normal automatic conversion of strings to numbers takes place, and everything “just works.”

However, gawk supports variables whose types are “regexp”. You can assign variables of this type using the following syntax:

gawk -v 're1=foo|bar/' '…' /path/to/file1 're2=baz|quux/' /path/to/file2

Strongly typed regexps are an advanced feature (see section Strongly Typed Regexp Constants). We mention them here only for completeness.