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authorStephane Chazelas <stephane.chazelas@gmail.com>2014-11-23 18:27:41 +0000
committerPeter Stephenson <p.w.stephenson@ntlworld.com>2014-11-23 18:29:09 +0000
commitff292af95f9bb6f07a56c162e583a145bbaa389d (patch)
tree0c52f30bf62a39eb76728f7a09fd383e81653606 /Etc
parent02bca2ea0fe47611644bfc1ca8b93f215317c97d (diff)
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33740: FAQ: another way of avoiding MULTIOs effects on pipes
Diffstat (limited to 'Etc')
-rw-r--r--Etc/FAQ.yo9
1 files changed, 8 insertions, 1 deletions
diff --git a/Etc/FAQ.yo b/Etc/FAQ.yo
index 7d4b86ec3..eeb7c13de 100644
--- a/Etc/FAQ.yo
+++ b/Etc/FAQ.yo
@@ -1784,7 +1784,14 @@ sect(Why is my output duplicated with `tt(foo 2>&1 >foo.out | bar)'?)
   to both files when the redirector appears twice.  What's going on in the
   first example is exactly the same, however the second redirector is
   disguised as a pipe.  So if you want to turn this effect off, you need
-  to unset the option mytt(MULTIOS).
+  to unset the option mytt(MULTIOS), or alternatively write the following:
+  verb(
+    % { print output; print error >&2 } 2>&1 >&- >foo.out | sed 's/error/erratic/'
+    erratic
+  )
+  By closing stdout with tt(>&-), we're cancelling the previous redirections
+  (to the pipe) and start anew with tt(>foo.out) instead of adding it as a
+  redirection target to stdout.
 
 
 sect(What are these `^' and `~' pattern characters, anyway?)