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Full Discussion: I/O redirection
Top Forums Shell Programming and Scripting I/O redirection Post 302502756 by alister on Tuesday 8th of March 2011 09:47:22 PM
Old 03-08-2011
http://www.tldp.org/LDP/abs/html/io-redirection.html
Quote:
Originally Posted by Advanced Bash Scripting Guide
Code:
# Redirecting only stderr to a pipe.

exec 3>&1                              # Save current "value" of stdout.
ls -l 2>&1 >&3 3>&- | grep bad 3>&-    # Close fd 3 for 'grep' (but not 'ls').
#              ^^^^   ^^^^
exec 3>&-                              # Now close it for the remainder of the script.

In my opinion, that's simply a poorly-worded comment on their part. fd 3 is closed for both. Perhaps what the author was trying to convey is that ls still has access to fd 3's destination because it was dup'd before closing (the >&3 before 3>&-). But, then, so does grep, since its inherited stdout leads to the same place as fd 3.

My advice would be to not get hung up on this example.

Regards,
Alister
 

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LEARN ABOUT PHP

zgrep

ZGREP(1)						      General Commands Manual							  ZGREP(1)

NAME

       zgrep - search possibly compressed files for a regular expression

SYNOPSIS

       zgrep [ grep_options ] [ -e ] pattern filename...

DESCRIPTION

       Zgrep  invokes  grep  on  compressed  or  gzipped  files.   These  grep	options  will  cause  zgrep  to  terminate  with  an  error  code:
       (-[drRzZ]|--di*|--exc*|--inc*|--rec*|--nu*).  All other options specified are passed directly to grep.  If no file is specified,  then  the
       standard input is decompressed if necessary and fed to grep.  Otherwise the given files are uncompressed if necessary and fed to grep.

       If the GREP environment variable is set, zgrep uses it as the grep program to be invoked.

EXIT CODE

       2 - An option that is not supported was specified.

AUTHOR

       Charles Levert (charles@comm.polymtl.ca)

SEE ALSO

       grep(1), gzexe(1), gzip(1), zdiff(1), zforce(1), zmore(1), znew(1)

																	  ZGREP(1)
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