In AWK, the `getline` function is used to read input from a file or command. The syntax of `getline` is:
getline [var] [file]
The `var` argument is the variable to store the input, and the `file` argument specifies the input file or command. If the `var` argument is omitted, `getline` reads the input into the default variable `$0`.
Here is an example of using `getline` to read input from a file:
awk '{
getline line < "file.txt"
print line
}' input.txt
In this example, we use `getline` to read a line from the file `file.txt`, and store it in the variable `line`. We then print the contents of `line` to the standard output. The input for the AWK program is taken from the file `input.txt`.
You can also use `getline` to read input from a command by using a pipe (`|`) to pass the output of the command to `getline`. Here is an example:
awk '{
cmd = "ls -l | sort"
while ((cmd | getline line) > 0) {
print line
}
close(cmd)
}' input.txt
In this example, we use `getline` to read the output of the command `ls -l | sort` into the variable `line`. We use a `while`loop to read each line of output until there is no more input, and then print each line to the standard output. We also use the `close` function to close the command after reading all of its output.
Note that when using `getline` with a file or command, you need to be careful about when you close the file or command. It is generally a good practice to close the file or command as soon as you are done reading from it, using the `close` function. This helps to avoid potential conflicts or errors when reading input from multiple files or commands.