Printing escaped values of control characters

miketosh has asked for the wisdom of the Perl Monks concerning the following question:

I'm looking for a simple way to output the escaped-values of certain control characters, such as carriage return and line feed.

Code:

my $string = "1\r\n 2 \n";
while ($string = /(.)/g) {
  print "Encountered character: $1\n";
}
[download]

My Desired output for the above code would be:

Encountered character: 1
Encountered character: \r
Encountered character: \n
Encountered character: \s
Encountered character: 2
Encountered character: \s
Encountered character: \n
[download]

Are there any known ways to get those values converted?

Comment on Printing escaped values of control characters Select or Download Code

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Re: Printing escaped values of control characters by Eliya (Vicar) on Aug 02, 2011 at 15:40 UTC
Just create a lookup table for whatever characters you consider to be control characters (why is space a control char?): `my %escaped = ( "\n" => '\n', "\r" => '\r', " " => '\s', # ... ); my $string = "1\r\n 2 \n"; while ($string =~ /(.)/sg) { my $ch = $1; $ch = $escaped{$ch} if exists $escaped{$ch}; print "Encountered character: $ch\n"; }` [download]	[reply] [d/l]
Re: Printing escaped values of control characters by Jim (Curate) on Aug 02, 2011 at 15:41 UTC
Use a simple lookup table—a hash—you initialize yourself. By the way, `\s` is not a character escape sequence; it's a regular expression pattern escape sequence. There's no general, one-to-one pairing of characters with regex patterns.	[reply] [d/l]
Re: Printing escaped values of control characters by johngg (Canon) on Aug 02, 2011 at 22:44 UTC
Using a lookup as suggested by Eliya and Jim but instead of using a regex capture it seems simpler to just split into individual characters and feed into a map doing a lookup in a ternary. `knoppix@Microknoppix:~$ perl -E ' > %esc = ( > qq{\n} => q{\n}, > qq{\r} => q{\r}, > q{ } => q{\s}, > ); > $str = qq{1\r\n 2 \n}; > say qq{Saw $_} for > map { exists $esc{ $_ } ? $esc{ $_ } : $_ } > split m{}, $str;' Saw 1 Saw \r Saw \n Saw \s Saw 2 Saw \s Saw \n knoppix@Microknoppix:~$` [download] I hope this is helpful. Cheers, JohnGG	[reply] [d/l]
Re: Printing escaped values of control characters by perl5ever (Pilgrim) on Aug 02, 2011 at 20:17 UTC
You can use `Data::Dumper` with `Useqq(1)`: `use Data::Dumper; sub to_string { Data::Dumper->new([])->Terse(1)->Indent(0)->Useqq(1)->Values([$_[0]] +)->Dump; } say to_string(chr(13)); # "\r" say to_string(chr(10)); # "\n" say to_string(chr(97)); # "a" say to_string(chr(31)); # "\37"` [download]	[reply] [d/l] [select]