Perl/sed Escape Syntax Problem . . .


 
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# 1  
Old 10-30-2014
Perl/sed Escape Syntax Problem . . .

Greetings!

I've run into this before; and am having a spot of trouble trying to figure out the way that Perl would prefer the following example syntax to be formed:
Code:
#!/usr/bin/perl

use strict;
use warnings;
use diagnostics;

`sed -i 's/Hi Mom!\|Hi Dad!/Bye Everyone!/I' ./test.txt`;

Perl doesn't throw a fit; but sed simply looks at you funny and does nothing at all...

So, while there are "sleeker" ways of handling this with pure perl, this type of issue has bugged me for a bit. Any ideas as to how one might pull things together syntaxwise to make it tick over???

Smilie

Thanks for the help, and have a great day!
# 2  
Old 10-30-2014
Try:
Code:
#!/usr/bin/perl

use strict;
use warnings;
use diagnostics;

`sed -i 's/Hi Mom!\\|Hi Dad!/Bye Everyone!/I' ./test.txt`;

This User Gave Thanks to bartus11 For This Post:
# 3  
Old 10-30-2014
You need two \\ because...
perl passes one \ to a shell,
the shell finds the \ within a 'string' and leaves it unchanged,
sed finds \|
Bingo.
If the shell would find the \ outside a 'string' it would quote the next character, so you would need \\\\ in your perl code -> Perl passes \\ to the shell -> the shell passes \ to sed -> sed finds \|
You should really do that in Perl...
This User Gave Thanks to MadeInGermany For This Post:
# 4  
Old 10-31-2014
Thanks, folks, for the clarifications and input.
Quote:
If the shell would find the \ outside a 'string' it would quote the next character, so you would need \\\\ in your perl code -> Perl passes \\ to the shell -> the shell passes \ to sed -> sed finds \|
You should really do that in Perl...
Thanks, MadeInGermany, for the smile. I do agree; but I also truly love Monty Python Smilie

Thanks again; and have a great weekend!
# 5  
Old 11-04-2014
You can also do something like this:
Code:
#!/usr/bin/perl

use strict;
use warnings;
use diagnostics;

qx'sed -i "s/Hi Mom!\|Hi Dad!/Bye Everyone!/I" ./test.txt';

No more double backslash, but you have to change the quote character in the sed command.
This User Gave Thanks to bartus11 For This Post:
# 6  
Old 11-04-2014
@bartus11:

Interesting and helpful!

What are we doing here; and what are the pros & cons of using this approach???

Smilie
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