4.9 Explicit Input with getline

So far we have been getting our input data from awk’s main input stream—either the standard input (usually your terminal, sometimes the output from another program) or from the files specified on the command line. The awk language has a special built-in command called getline that can be used to read input under your explicit control.

The getline command is used in several different ways and should not be used by beginners. The examples that follow the explanation of the getline command include material that has not been covered yet. Therefore, come back and study the getline command after you have reviewed the rest of this Web page and have a good knowledge of how awk works.

The getline command returns one if it finds a record and zero if it encounters the end of the file. If there is some error in getting a record, such as a file that cannot be opened, then getline returns -1. In this case, gawk sets the variable ERRNO to a string describing the error that occurred.

In the following examples, command stands for a string value that represents a shell command.

NOTE: When ‘--sandbox’ is specified (see section Command-Line Options), reading lines from files, pipes and coprocesses is disabled.