5.3.2 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 Other 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 are run. The -v option and its assignment must precede all the file name arguments, as well as the program text. (See 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 BBS-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 the file 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 BBS-list:

     $ awk '{ print $n }' n=4 inventory-shipped n=2 BBS-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 ARGC and ARGV). awk processes the values of command-line assignments for escape sequences (see Escape Sequences). (d.c.)