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Full Discussion: Named pipe hanging?
Top Forums UNIX for Dummies Questions & Answers Named pipe hanging? Post 302893545 by Ditto on Wednesday 19th of March 2014 04:25:46 PM
Old 03-19-2014
Quote:
Originally Posted by Corona688
The shell tries to open the pipe before it puts the command in background, and freezes waiting for it. You have to put it in a separate subshell to avoid this.

Code:
( command < pipe ) &

Yes, the tee command, I run using & to throw into background.
As I indicated, if you comment out the ls (which seems to have nothing to do with the PIPE - it works fine - no hang.
With the script as is - the first echo makes it into the pipe, the ls works fine - displays to screen only.
then the last echo just hangs. Yes - my script is hanging.

Quote:
What is your goal here, though?

What I'm trying to do:
- want to capture stdout and sterr to both display and log file
- need to capture the return code of the command as well (ie $?) (hence why I'm mucking around with PIPE's so I can displace the tee command).
 

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SHELL-QUOTE(1)						User Contributed Perl Documentation					    SHELL-QUOTE(1)

NAME
shell-quote - quote arguments for safe use, unmodified in a shell command SYNOPSIS
shell-quote [switch]... arg... DESCRIPTION
shell-quote lets you pass arbitrary strings through the shell so that they won't be changed by the shell. This lets you process commands or files with embedded white space or shell globbing characters safely. Here are a few examples. EXAMPLES
ssh preserving args When running a remote command with ssh, ssh doesn't preserve the separate arguments it receives. It just joins them with spaces and passes them to "$SHELL -c". This doesn't work as intended: ssh host touch 'hi there' # fails It creates 2 files, hi and there. Instead, do this: cmd=`shell-quote touch 'hi there'` ssh host "$cmd" This gives you just 1 file, hi there. process find output It's not ordinarily possible to process an arbitrary list of files output by find with a shell script. Anything you put in $IFS to split up the output could legitimately be in a file's name. Here's how you can do it using shell-quote: eval set -- `find -type f -print0 | xargs -0 shell-quote --` debug shell scripts shell-quote is better than echo for debugging shell scripts. debug() { [ -z "$debug" ] || shell-quote "debug:" "$@" } With echo you can't tell the difference between "debug 'foo bar'" and "debug foo bar", but with shell-quote you can. save a command for later shell-quote can be used to build up a shell command to run later. Say you want the user to be able to give you switches for a command you're going to run. If you don't want the switches to be re-evaluated by the shell (which is usually a good idea, else there are things the user can't pass through), you can do something like this: user_switches= while [ $# != 0 ] do case x$1 in x--pass-through) [ $# -gt 1 ] || die "need an argument for $1" user_switches="$user_switches "`shell-quote -- "$2"` shift;; # process other switches esac shift done # later eval "shell-quote some-command $user_switches my args" OPTIONS
--debug Turn debugging on. --help Show the usage message and die. --version Show the version number and exit. AVAILABILITY
The code is licensed under the GNU GPL. Check http://www.argon.org/~roderick/ or CPAN for updated versions. AUTHOR
Roderick Schertler <roderick@argon.org> perl v5.16.3 2010-06-11 SHELL-QUOTE(1)
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