close()’s Return Value ¶In many older versions of Unix awk, the close() function
is actually a statement.
(d.c.)
It is a syntax error to try and use the return
value from close():
command = "..." command | getline info retval = close(command) # syntax error in many Unix awks
gawk treats close() as a function.
The return value is −1 if the argument names something
that was never opened with a redirection, or if there is
a system problem closing the file or process.
In these cases, gawk sets the predefined variable
ERRNO to a string describing the problem.
In gawk, starting with version 4.2, when closing a pipe or
coprocess (input or output), the return value is the exit status of the
command, as described in Table 5.1.31 Otherwise, it is the return value from the system’s close()
or fclose() C functions when closing input or output files,
respectively. This value is zero if the close succeeds, or −1
if it fails.
Recent versions of BWK awk also return the same values
from close().
| Situation | Return value from close() |
|---|---|
| Normal exit of command | Command’s exit status |
| Death by signal of command | 256 + number of murderous signal |
| Death by signal of command with core dump | 512 + number of murderous signal |
| Some kind of error | −1 |
Table 5.1: Return values from close() of a pipe
The POSIX standard is very vague; it says that close()
returns zero on success and a nonzero value otherwise. In general,
different implementations vary in what they report when closing
pipes; thus, the return value cannot be used portably.
(d.c.)
In POSIX mode (see Command-Line Options), gawk just returns zero
when closing a pipe.
Prior
to version 4.2, the return value from closing a pipe or co-process
was the full 16-bit exit value as defined by the wait() system
call.