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Top Forums Shell Programming and Scripting Diamond operator in Until Statement (perl) Post 302267450 by radoulov on Friday 12th of December 2008 10:51:55 AM
Old 12-12-2008
Quote:
Originally Posted by erichpowell
f you don't mind, I have a couple questions to start with:

1) How does this line of code work:
Code:
/^ID   (\w+)/ and $Gene = $1;

I think it's saying: if the regEx finds a match, assign what's in the parenthesis to $Gene.
[...]
I just don't understand how you are able to do make a conditional statement
without an 'if ' construct. Can you please elaborate on how this works?
Sure.
The && and || (and and and or) are also called "Short Circuit" operators.
From Perl Idioms Explained - && and || "Short Circuit" operators (actually the Camel Book):

Quote:
Camel II tells us that the term "Short-Circuit"
refers to the fact that they "determine the truth of the statement
by evaluating the fewest number of operands possible."
So essentially these operators stop the chain of evaluation
of an expression as early as possible.
That is another key to their value.
So only if the fisrt expression returns true (i.e. if there is a match)
evaluate the second one (i.e. set $Gene to $1).

Quote:
Code:
if (/^CC   -!- FUNCTION:/../CC   -!- SUBCELLULAR/) {

It seems like this regEx contains four slashes.
I've never seen one like that.
I assume this is used to get the text
in between FUNCTION and SUBCELLULAR, but again,
I just don't understand how it works.
Right, it's simply the range .. operator:

Code:
$ print '
junk
start
yes
yes
end
junk
'|perl -ne'print if/start/../end/'
start
yes
yes
end

(see perldoc perlop | less -p'range operator' for more).
 

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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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