[GRASS-dev] Re: [GRASS GIS] #181: tac command missing in OSX

[GRASS GIS]

#181: tac command missing in OSX
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  Reporter:  kyngchaos  |       Owner:  grass-dev at lists.osgeo.org
      Type:  defect     |      Status:  new                      
  Priority:  minor      |   Milestone:  6.3.1                    
 Component:  default    |     Version:  6.3.0                    
Resolution:             |    Keywords:  v.in.garmin, v.in.mapgen 
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Comment (by 1gray):

 Replying to [comment:3 kyngchaos]:
 > Replying to [comment:2 hamish]:
 > > Can the Mac build provide a copy of tac somehow? (or just
 automatically apply the 'tail -r' patches with your build..)

 > I ''could'' provide a copy or patch it in my binary, but that's just a
 packager's solution, and those who build from source would still have to
 deal with it somehow.  tac is annoying in that it's part of a GNU bundle,
 core-utilities, I couldn't find only tac source.  And my first
 quick-n-dirty attempt to compile it failed.

 That's how most bundles work.  One couldn't, e. g., easily compile
 `r.what` without compiling the rest of GRASS as well.

 > How about testing for the -r flag, as I mentioned?  A non-existent
 option on OSX returns `tail: illegal option xxx` plus a usage string with
 the available flags.  What about other versions of tail?  Or can you thing
 of a good way to test for the flag?  If anything, I could test for
 uname=Darwin (tho that's awfully specific).

 I'd recommend to check for the existence of `tac` instead, like
 (untested):
 {{{
 search_for_executable () {
     echo "$PATH" | tr : \\n | while read _search_for_executable_dir ; do
         if [ -x "$_search_for_executable_dir/$1" ]; then
             echo "$_search_for_executable_dir/$1"
             break
         fi
     done
 }

 if [ -n "$TAC" ]; then
     TAC=tac
 else
     TAC=$(search_for_executable "tac")
 fi

 if [ -z "$TAC" ]; then
     ## no `tac' found, fall back to `tail -r' instead
     TAC="tail -r"
 fi

 ...

 $TAC arguments...
 }}}

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Ticket URL: <https://trac.osgeo.org/grass/ticket/181#comment:4>
GRASS GIS <http://grass.osgeo.org>