Well, if you ran my test program (see above) on unix and got different results than I did, then I will have to defer to an observable fact that different versions of perl handle this differently. But on all the unix machines I've tested this on, it is 100% consistent (I will concede that Windows perl handles this differently).

Plus, the docs for $! state "after a failure". There is no definition for "failure" given, but I assume it means after readline returns undef, which it does on both EOF and I/O error. Therefore, it is valid to check the value of $! in the case under consideration, since readline has returned undef.

Could you please post the output of "uname -a" on the version of unix where you ran my test program and the version of perl you used to run it? Here are my results for a variety of perl versions and unices, plus Windows XP. The only version that displays the strange behavior of modifying $! on EOF is Windows XP. 

AIX 5.2
This is perl, version 5.005_03 built for aix
n=5 s=I/O error
n=6 s=No such device or address
n=0 s=
This is perl, v5.8.0 built for aix-thread-multi
n=5 s=I/O error
n=6 s=No such device or address
n=0 s=

AIX 5.3
This is perl, v5.8.2 built for aix-thread-multi
n=5 s=I/O error
n=6 s=No such device or address
n=0 s=

SunOS 5.8
This is perl, version 5.005_03 built for sun4-solaris
n=5 s=I/O error
n=6 s=No such device or address
n=0 s=
This is perl, v5.6.0 built for sun4-solaris
n=5 s=I/O error
n=6 s=No such device or address
n=0 s=

SunOS 5.9
This is perl, version 5.005_03 built for sun4-solaris
n=5 s=I/O error
n=6 s=No such device or address
n=0 s=
This is perl, v5.6.0 built for sun4-solaris
n=5 s=I/O error
n=6 s=No such device or address
n=0 s=
This is perl, v5.6.1 built for sun4-solaris-64int
n=5 s=I/O error
n=6 s=No such device or address
n=0 s=

Linux 2.4.2-2
This is perl, v5.6.0 built for i386-linux
n=5 s=Input/output error
n=6 s=No such device or address
n=0 s=

Linux 2.4.21-47.0.1.ELsmp
This is perl, v5.8.0 built for i386-linux-thread-multi
n=5 s=Input/output error
n=6 s=No such device or address
n=0 s=

CYGWIN_NT-5.1 1.5.19(0.150/4/2)
This is perl, v5.8.7 built for cygwin-thread-multi-64int
n=5 s=Input/Output error
n=6 s=No such device or address
n=0 s=

Windows XP
This is perl, v5.8.7 built for MSWin32-x86-multi-thread
n=0 s=
n=0 s=
n=0 s=

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In reply to Re^8: Best way to handle readline errors? by jrw
in thread Best way to handle readline errors? by jrw

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