getline ¶So far we have been getting our input data from awk’s main
input stream—either the standard input (usually your keyboard, sometimes
the output from another program) or the
files specified on the command line. The awk language has a
special built-in function called getline that
can be used to read input under your explicit control.
The getline function is used in several different ways and should
not be used by beginners.
The examples that follow the explanation of the getline function
include material that has not been covered yet. Therefore, come back
and study the getline function after you have reviewed the
rest of
this Web page
and have a good knowledge of how awk works.
The getline function returns 1 if it finds a record and 0 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.
If ERRNO indicates that the I/O operation may be
retried, and PROCINFO["input", "RETRY"] is set,
then getline returns −2
instead of −1, and further calls to getline
may be attempted. See Retrying Reads After Certain Input Errors for further information about
this feature.
In the following examples, command stands for a string value that represents a shell command.
NOTE: When --sandbox is specified (see Command-Line Options), reading lines from files, pipes, and coprocesses is disabled.
getline with No Argumentsgetline into a Variablegetline from a Filegetline into a Variable from a Filegetline from a Pipegetline into a Variable from a Pipegetline from a Coprocessgetline into a Variable from a Coprocessgetlinegetline Variants