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Top Forums Shell Programming and Scripting AWK Script and Commandline difference Post 302535023 by Corona688 on Wednesday 29th of June 2011 11:37:21 AM
Old 06-29-2011
Quote:
Originally Posted by yazu
I wrote about quoting shell variables not about embedding.

Maybe you true about awk but the "pretty bad" way is universal
It's a bad idea because it becomes language syntax, not merely a string. This is especially bad for a variable, where you might not have strict control over the exact contents:
Code:
$ STR="hello 'world'"
$ awk 'BEGIN { print "'$STR'" }'
awk: BEGIN { print "hello
awk:               ^ unterminated string
$

Quote:
it's for perl
Code:
 VAR="this will barf'"
# subsitute in the shell and it barfs, taking the extra ' as perl syntax
$ perl -e "print '$VAR', "\n";'
Can't find string terminator '"' anywhere before EOF at -e line 1.
# do it properly and it will not.
$ perl -e 'print shift, "\n"' "$VAR"
this will barf'
$

Quote:
...sed, python or almost anything other, where you want to embed shell variables.
I admit there's no good way to do it in sed, but this is an argument against sed, not an argument for that syntax. It's very difficult to safely put variables in sed because so many things need escaping.

And if the argument is that you don't need to memorize syntax for each language, well, you already had to memorize -e for perl, how much harder is -v, shift, etc?

Last edited by Corona688; 06-29-2011 at 12:42 PM..
 

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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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