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AWK Script and Commandline difference

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# 8  
Old 06-29-2011
Quote:
Code:
$ STR="hello 'world'"
$ awk 'BEGIN { print "'$STR'" }'

But i wrote exactly about this! Put shell variables inside double quotes:

Code:
$ STR="hello 'world'"
app@kf3sv ~
$ awk 'BEGIN { print "'"$STR"'" }'
hello 'world'

Code:
$ perl -e 'print "'"$VAR"'", "\n";'
this will barf'

And yes - threre is not an universal "safe" way to embed shell variables. But I believe there is not any universal way to write "safe" shell scripts. Shell is a command language, you know - for those who write and execute commands.

And I repeat one more:
The inner double quotes are really not needed here but this is a good habit.
# 9  
Old 06-29-2011
Quote:
Originally Posted by yazu
But i wrote exactly about this! Put shell variables inside double quotes:

Code:
$ STR="hello 'world'"
app@kf3sv ~
$ awk 'BEGIN { print "'"$STR"'" }'
hello 'world'

Okay, how about:

Code:
$ STR="hello \"world\""
$ awk 'BEGIN { print "'"$STR"'" }'
hello
$ STR='"; system("/sbin/poweroff") ; print "'
$ awk 'BEGIN { print "'"$STR"'" }'

poweroff: must be superuser.

$ awk -v VAR="$STR" 'BEGIN { print VAR }'
"; system("/sbin/poweroff") ; print "
$

Extra quotes don't protect you no matter how many of them you have. They do leave you wide open to bizzare errors and intentional abuse. The -v syntax eliminates all these problems.
Quote:
And yes - threre is not an universal "safe" way to embed shell variables.
Your method isn't merely imperfect, it's downright unsafe.
# 10  
Old 06-29-2011
Well, enough. Just only - it is not my method - it's common practice to embed shell variables in perl, sed, sql etc.
# 11  
Old 06-29-2011
If it really is "common practice" that's alarming.

I don't understand your defensiveness. There may be situations where substituting strings into the program text itself is the only option(I already demonstrated how to avoid that in perl with shift), but this topic, about awk, isn't one of them.
Last edited by Corona688; 06-29-2011 at 01:39 PM..
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