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Top Forums Shell Programming and Scripting Print certain lines based on condition Post 302844034 by Don Cragun on Friday 16th of August 2013 07:20:30 AM
Old 08-16-2013
Originally Posted by Scrutinizer
Hi Don,

I don't think that is correct:

awk: Variables and Special Variables
Thanks Scrutinizer,
I stand corrected. The behavior is defined when RS is an empty string.

The behavior is unspecified when FS is an empty string. (And, it is fairly common to find scripts in these forums that assume that FS= will make every character on a line be a separate field. I confused this issue with FS when I was talking about RS. I obviously need to get some sleep.)

Last edited by Don Cragun; 08-16-2013 at 08:21 AM.. Reason: fix typo
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SHELL-QUOTE(1)						User Contributed Perl Documentation					    SHELL-QUOTE(1)

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 or CPAN for updated versions. AUTHOR
Roderick Schertler <> perl v5.16.3 2010-06-11 SHELL-QUOTE(1)

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