I have a string,
$str = abc#$and#def
I tried to replace '$' with it's hex value using ,
$str=~s/$/%26/g
But the output is abc#.
This might be because '$'is considered as the end of the line or string.
Please let me know
Your problem is nothing to do with your substitution; when you are assigning to the string in the first place:
$str = "abc#$and#def";
$and and #def are treated as variables to interpolate.
You need to escape the sigils or use single quotes (which don't interpolate variables):
$str = 'abc#$and#def';
# or
$str = "abc#\$and\#def";
And you really really need to enable warnings, which would have told you your assignment was the problem.
You need to escape the $ with a \
$str =~ s/\$/%26/g
Try escaping the $ with a \:
$str =~ s/\$/%26/g;
Ron
Related
I have a variable that contains a slash and a t.
my $var = "\\t";
I want to convert that to a tab. How do I do that?
use Data::Dumper;
use Term::ReadLine;
my $rl = Term::ReadLine->new();
my $var = $rl->readline( 'Enter \t:' );
print Dumper $var;
The following is the simplest solution:
$var = "\t" if $var eq "\\t";
If you want to do this no matter where the sequence appears in the string, you could use
$var =~ s/\\t/\t/g;
But it sounds like you're not asking the right question. Nothing supports \t and nothing else. At the very least, I would also expect \\ to produce \. Are you perhaps trying to parse JSON? If so, there are number of other escape sequences you need to worry about.
my code is as follows
my $string = $cells[71];
print $string;
this prints the string but where spaces should be there is a box with 01 10 in it. I opened it in Notepad++ and the box turned into a black GS (which i am assuming is group separator).
I looked online and it said to use:
s/[^[:print:]]+//g
but when i set the string to:
my $string =~s/[^[:print:]]+//g
and I run the program i get:
4294967295
How do i resolve this?
I did what HOBBS said and it worked... thanks :)
Is there anyway I could print an enter where each of these characters are ( the box with 1001)?
When doing a regex match, you need to be careful to write $var =~ /pattern/, not $var = ~ /pattern/. When you use the second one, you're doing /pattern/, which is a regex match against $_, returning a number in scalar context. Then you do ~, which takes the bitwise inverse of that number, then ($var =) you assign that result to $var. Not what you wanted at all.
You have to assign the variable first, then do the substitution:
my $string = $cells[71];
$string =~ s/[^[:print:]]+//g;
For example I have,
my $str = '\t';
print "My String is ".$str;
I want the output to interpret the tab character and return something like:
"My String is \t"
I am actually getting the value of the string from the database, and it returns it as a single quoted string.
String::Interpolate does exactly that
$ perl -MString::Interpolate=interpolate -E 'say "My String is [". interpolate(shift) . "]"' '\t'
My String is [ ]
'\t' and "\t" are string literals, pieces of Perl code that produces strings ("\","t" and the tab character respectively). The database doesn't return Perl code, so describing the problem in terms of single-quoted literals and double-quoted literals makes no sense. You have a string, period.
The string is formed of the characters "\" and "t". You want to convert that sequence of characters into the tab character. That's a simple substitution.
s/\\t/\t/g
I presume you don't want to deal with just \t. You can create a table of the sequences.
my %escapes = (
"t" => "\t",
"n" => "\n",
"\" => "\\",
);
my $escapes_pat = join('', map quotemeta, keys(%escapes));
$escapes_pat = qr/[$escapes_pat]/;
s/\\($escapes_pat)/$escapes{$1}/g;
You can follow the technique in perlfaq4's answer to How can I expand variables in text strings?:
If you can avoid it, don't, or if you can use a templating system, such as Text::Template or Template Toolkit, do that instead. You might even be able to get the job done with sprintf or printf:
my $string = sprintf 'Say hello to %s and %s', $foo, $bar;
However, for the one-off simple case where I don't want to pull out a full templating system, I'll use a string that has two Perl scalar variables in it. In this example, I want to expand $foo and $bar to their variable's values:
my $foo = 'Fred';
my $bar = 'Barney';
$string = 'Say hello to $foo and $bar';
One way I can do this involves the substitution operator and a double /e flag. The first /e evaluates $1 on the replacement side and turns it into $foo. The second /e starts with $foo and replaces it with its value. $foo, then, turns into 'Fred', and that's finally what's left in the string:
$string =~ s/(\$\w+)/$1/eeg; # 'Say hello to Fred and Barney'
The /e will also silently ignore violations of strict, replacing undefined variable names with the empty string. Since I'm using the /e flag (twice even!), I have all of the same security problems I have with eval in its string form. If there's something odd in $foo, perhaps something like #{[ system "rm -rf /" ]}, then I could get myself in trouble.
To get around the security problem, I could also pull the values from a hash instead of evaluating variable names. Using a single /e, I can check the hash to ensure the value exists, and if it doesn't, I can replace the missing value with a marker, in this case ??? to signal that I missed something:
my $string = 'This has $foo and $bar';
my %Replacements = (
foo => 'Fred',
);
# $string =~ s/\$(\w+)/$Replacements{$1}/g;
$string =~ s/\$(\w+)/
exists $Replacements{$1} ? $Replacements{$1} : '???'
/eg;
print $string;
Well, I just tried below workaround it worked. Please have a look
my $str1 = "1234\n\t5678";
print $str1;
#it prints
#1234
# 5678
$str1 =~ s/\t/\\t/g;
$str1 =~ s/\n/\\n/g;
print $str1;
#it prints exactly the same
#1234\n\t5678
In perl suppose I have a string like 'hello\tworld\n', and what I want is:
'hello world
'
That is, "hello", then a literal tab character, then "world", then a literal newline. Or equivalently, "hello\tworld\n" (note the double quotes).
In other words, is there a function for taking a string with escape sequences and returning an equivalent string with all the escape sequences interpolated? I don't want to interpolate variables or anything else, just escape sequences like \x, where x is a letter.
Sounds like a problem that someone else would have solved already. I've never used the module, but it looks useful:
use String::Escape qw(unbackslash);
my $s = unbackslash('hello\tworld\n');
You can do it with 'eval':
my $string = 'hello\tworld\n';
my $decoded_string = eval "\"$string\"";
Note that there are security issues tied to that approach if you don't have 100% control of the input string.
Edit: If you want to ONLY interpolate \x substitutions (and not the general case of 'anything Perl would interpolate in a quoted string') you could do this:
my $string = 'hello\tworld\n';
$string =~ s#([^\\A-Za-z_0-9])#\\$1#gs;
my $decoded_string = eval "\"$string\"";
That does almost the same thing as quotemeta - but exempts '\' characters from being escaped.
Edit2: This still isn't 100% safe because if the last character is a '\' - it will 'leak' past the end of the string though...
Personally, if I wanted to be 100% safe I would make a hash with the subs I specifically wanted and use a regex substitution instead of an eval:
my %sub_strings = (
'\n' => "\n",
'\t' => "\t",
'\r' => "\r",
);
$string =~ s/(\\n|\\t|\\n)/$sub_strings{$1}/gs;
In Perl, what is the difference between ' and " ?
For example, I have 2 variables like below:
$var1 = '\(';
$var2 = "\(";
$res1 = ($matchStr =~ m/$var1/);
$res2 = ($matchStr =~ m/$var2/);
The $res2 statement complains that Unmatched ( before HERE mark in regex m.
Double quotes use variable expansion. Single quotes don't
In a double quoted string you need to escape certain characters to stop them being interpreted differently. In a single quoted string you don't (except for a backslash if it is the final character in the string)
my $var1 = 'Hello';
my $var2 = "$var1";
my $var3 = '$var1';
print $var2;
print "\n";
print $var3;
print "\n";
This will output
Hello
$var1
Perl Monks has a pretty good explanation of this here
' will not resolve variables and escapes
" will resolve variables, and escape characters.
If you want to store your \ character in the string in $var2, use "\\("
Double quotation marks interpret, and single quotation do not
If you are going to create regex strings you should really be using the qr// quote-like operator:
my $matchStr = "(";
my $var1 = qr/\(/;
my $res1 = ($matchStr =~ m/$var1/);
It creates a compiled regex that is much faster than just using a variable containing string. It also will return a string if not used in a regex context, so you can say things like
print "$var1\n"; #prints (?-xism:\()
Perl takes the single-quoted strings 'as is' and interpolates the double-quoted strings. Interpolate means, that it substitutes variables with variable values, and also understands escaped characters. So, your "\(" is interpreted as '(', and your regexp becomes m/(/, this is why Perl complains.
"" Supports variable interpolation and escaping. so inside "\(" \ escapes (
Where as ' ' does not support either. So '\(' is literally \(