nextfile Statement ¶The nextfile statement
is similar to the next statement.
However, instead of abandoning processing of the current record, the
nextfile statement instructs awk to stop processing the
current data file.
Upon execution of the nextfile statement,
FILENAME is
updated to the name of the next data file listed on the command line,
FNR is reset to one,
and processing
starts over with the first rule in the program.
If the nextfile statement causes the end of the input to be reached,
then the code in any END rules is executed. An exception to this is
when nextfile is invoked during execution of any statement in an
END rule; in this case, it causes the program to stop immediately.
See The BEGIN and END Special Patterns.
The nextfile statement is useful when there are many data files
to process but it isn’t necessary to process every record in every file.
Without nextfile,
in order to move on to the next data file, a program
would have to continue scanning the unwanted records. The nextfile
statement accomplishes this much more efficiently.
In gawk, execution of nextfile causes additional things
to happen: any ENDFILE rules are executed if gawk is
not currently in an END rule, ARGIND is
incremented, and any BEGINFILE rules are executed. (ARGIND
hasn’t been introduced yet. See Predefined Variables.)
There is an additional, special, use case
with gawk. nextfile is useful inside a BEGINFILE
rule to skip over a file that would otherwise cause gawk
to exit with a fatal error. In this special case, ENDFILE rules are not
executed. See The BEGINFILE and ENDFILE Special Patterns.
Although it might seem that ‘close(FILENAME)’ would accomplish
the same as nextfile, this isn’t true. close() is
reserved for closing files, pipes, and coprocesses that are
opened with redirections. It is not related to the main processing that
awk does with the files listed in ARGV.
NOTE: For many years,
nextfilewas a common extension. In September 2012, it was accepted for inclusion into the POSIX standard. See the Austin Group website.
The current version of BWK awk and mawk
also support nextfile. However, they don’t allow the
nextfile statement inside function bodies (see User-Defined Functions).
gawk does; a nextfile inside a function body reads the
first record from the next file and starts processing it with the first
rule in the program, just as any other nextfile statement.