Gawk/Getline
Next: Read Timeout, Previous: Multiple Line, Up: Reading Files [Contents][Index]
4.10 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 keyboard, sometimes
the output from another program) or 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 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 section 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
--sandboxis specified (see section Command-Line Options),reading lines from files, pipes, and coprocesses is disabled.
| • Plain Getline | Using getline with no arguments.
| |
| • Getline/Variable | Using getline into a variable.
| |
| • Getline/File | Using getline from a file.
| |
| • Getline/Variable/File | Using getline into a variable from a
file. | |
| • Getline/Pipe | Using getline from a pipe.
| |
| • Getline/Variable/Pipe | Using getline into a variable from a
pipe. | |
| • Getline/Coprocess | Using getline from a coprocess.
| |
| • Getline/Variable/Coprocess | Using getline into a variable from a
coprocess. | |
| • Getline Notes | Important things to know about getline.
| |
| • Getline Summary | Summary of getline Variants.
|
Next: Read Timeout, Previous: Multiple Line, Up: Reading Files [Contents][Index]
