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(head invocation, tail invocation, sort invocation):

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Give advice about porting to hosts that support only obsolete syntax.
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Paul Eggert
2006-05-03 23:10:04 +00:00
parent b400a630ae
commit c1f85fb9e1
2 changed files with 38 additions and 14 deletions
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doc/ChangeLog
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@@ -1,3 +1,9 @@
2006-05-03 Paul Eggert <eggert@cs.ucla.edu>
* coreutils.texi (head invocation, tail invocation, sort invocation):
Give advice about porting to hosts that support only obsolete syntax.
Problem reported by Zack Weinberg.
2006-04-23 Francesco Montorsi <fr_m@hotmail.com>
* coreutils.texi (Which files are listed): Describe new option:
doc/coreutils.texi
+32 -14
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@@ -2435,8 +2435,11 @@ For compatibility @command{head} also supports an obsolete option syntax
specified first. @var{count} is a decimal number optionally followed
by a size letter (@samp{b}, @samp{k}, @samp{m}) as in @option{-c}, or
@samp{l} to mean count by lines, or other option letters (@samp{cqv}).
New scripts should use @option{-c @var{count}} or @option{-n
@var{count}} instead.
Scripts intended for standard hosts should use @option{-c @var{count}}
or @option{-n @var{count}} instead. If your script must also run on
hosts that support only the obsolete syntax, it is usually simpler to
avoid @command{head}, e.g., by using @samp{sed 5q} instead of
@samp{head -5}.
@exitstatus
@@ -2620,8 +2623,6 @@ file. In the option, @var{count} is an optional decimal number optionally
followed by a size letter (@samp{b}, @samp{c}, @samp{l}) to mean count
by 512-byte blocks, bytes, or lines, optionally followed by @samp{f}
which has the same meaning as @option{-f}.
New scripts should use @option{-c @var{count}[b]},
@option{-n @var{count}}, and/or @option{-f} instead.
@vindex _POSIX2_VERSION
On older systems, the leading @samp{-} can be replaced by @samp{+} in
@@ -2629,12 +2630,24 @@ the obsolete option syntax with the same meaning as in counts, and
obsolete usage overrides normal usage when the two conflict.
This obsolete behavior can be enabled or disabled with the
@env{_POSIX2_VERSION} environment variable (@pxref{Standards
conformance}), but portable scripts should avoid commands whose
behavior depends on this variable.
For example, use @samp{tail -- - main.c} or @samp{tail main.c} rather than
the ambiguous @samp{tail - main.c}, @samp{tail -c4} or @samp{tail -c 10
4} rather than the ambiguous @samp{tail -c 4}, and @samp{tail ./+4}
or @samp{tail -n +4} rather than the ambiguous @samp{tail +4}.
conformance}).
Scripts intended for use on standard hosts should avoid obsolete
syntax and should use @option{-c @var{count}[b]}, @option{-n
@var{count}}, and/or @option{-f} instead. If your script must also
run on hosts that support only the obsolete syntax, you can often
rewrite it to avoid problematic usages, e.g., by using @samp{sed -n
'$p'} rather than @samp{tail -1}. If that's not possible, the script
can use a test like @samp{if tail -c +1 </dev/null >/dev/null 2>&1;
then @dots{}} to decide which syntax to use.
Even if your script assumes the standard behavior, you should still
beware usages whose behaviors differ depending on the @acronym{POSIX}
version. For example, avoid @samp{tail - main.c}, since it might be
interpreted as either @samp{tail main.c} or as @samp{tail -- -
main.c}; avoid @samp{tail -c 4}, since it might mean either @samp{tail
-c4} or @samp{tail -c 10 4}; and avoid @samp{tail +4}, since it might
mean either @samp{tail ./+4} or @samp{tail -n +4}.
@exitstatus
@@ -3662,10 +3675,15 @@ On older systems, @command{sort} supports an obsolete origin-zero
syntax @samp{+@var{pos1} [-@var{pos2}]} for specifying sort keys.
This obsolete behavior can be enabled or disabled with the
@env{_POSIX2_VERSION} environment variable (@pxref{Standards
conformance}), but portable scripts should avoid commands whose
behavior depends on this variable.
For example, use @samp{sort ./+2} or @samp{sort -k 3} rather than
the ambiguous @samp{sort +2}.
conformance}).
Scripts intended for use on standard hosts should avoid obsolete
syntax and should use @option{-k} instead. For example, avoid
@samp{sort +2}, since it might be interpreted as either @samp{sort
./+2} or @samp{sort -k 3}. If your script must also run on hosts that
support only the obsolete syntax, it can use a test like @samp{if sort
-k 1 </dev/null >/dev/null 2>&1; then @dots{}} to decide which syntax
to use.
Here are some examples to illustrate various combinations of options.