Nonfatal (The GNU Awk User’s Guide)
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5.10 Enabling Nonfatal Output
This section describes a gawk
-specific feature.
In standard awk
, output with print
or printf
to a nonexistent file, or some other I/O error (such as filling up the disk) is a fatal error.
$ gawk 'BEGIN { print "hi" > "/no/such/file" }' error→ gawk: cmd. line:1: fatal: can't redirect to `/no/such/file' (No error→ such file or directory)
gawk
makes it possible to detect that an error has occurred, allowing you to possibly recover from the error, or at least print an error message of your choosing before exiting. You can do this in one of two ways:
- For all output files, by assigning any value to
PROCINFO["NONFATAL"]
. - On a per-file basis, by assigning any value to
PROCINFO[filename, "NONFATAL"]
. Here,filename
is the name of the file to which you wish output to be nonfatal.
Once you have enabled nonfatal output, you must check ERRNO
after every relevant print
or printf
statement to see if something went wrong. It is also a good idea to initialize ERRNO
to zero before attempting the output. For example:
$ gawk ' > BEGIN { > PROCINFO["NONFATAL"] = 1 > ERRNO = 0 > print "hi" > "/no/such/file" > if (ERRNO) { > print("Output failed:", ERRNO) > "/dev/stderr" > exit 1 > } > }' error→ Output failed: No such file or directory
Here, gawk
did not produce a fatal error; instead it let the awk
program code detect the problem and handle it.
This mechanism works also for standard output and standard error. For standard output, you may use PROCINFO["-", "NONFATAL"]
or PROCINFO["/dev/stdout", "NONFATAL"]
. For standard error, use PROCINFO["/dev/stderr", "NONFATAL"]
.
When attempting to open a TCP/IP socket (see section Using gawk for Network Programming), gawk
tries multiple times. The GAWK_SOCK_RETRIES
environment variable (see section Other Environment Variables) allows you to override gawk
’s builtin default number of attempts. However, once nonfatal I/O is enabled for a given socket, gawk
only retries once, relying on awk
-level code to notice that there was a problem.
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