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Editorial Team
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Asked: 2026-06-14T16:45:41+00:00

The ‘N’ command in sed works differently with Cygwin’s sed(GNU sed I think) &

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The ‘N’ command in sed works differently with Cygwin’s sed(GNU sed I think) & AIX’s sed.

$cat > input
Apple
$cat input
Apple
$sed 'N' input
$cat > input
Apple
Orange
$sed 'N' input
Apple
Orange
$

As seen above, the first sed 'N' input command printed nothing for AIX’s sed as there was no new input line. However Cygwin’s sed printed Apple for the same.
Can some unix/sed guru throw some light into this? Thanks in advance.

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1 Answer

  1. Editorial Team

    It looks like AIX is behaving correctly, as per the POSIX standard (my italics):

    [2addr]N

    Append the next line of input, less its terminating < newline >, to the pattern space, using an embedded < newline > to separate the appended material from the original material. Note that the current line number changes.

    If no next line of input is available, the N command verb shall branch to the end of the script and quit without starting a new cycle or copying the pattern space to standard output.

    This is from http://pubs.opengroup.org/onlinepubs/009695399/utilities/sed.html.

    So, you’ve probably found a bug (or a least a non-conformance to POSIX) in GNU sed.

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