How do I remove white space in a Perl string?

Question

If I declared a variable $myString with the value '3 ' (notice the white space). Is there any function to remove the white space for the return value. A little like SomeFun($myString) then return '3' (without white space).

#!C:\Perl\bin\perl.exe
use strict;
use warnings;
use Data::Dumper; 

my $fh = \*DATA; 

print Dumper parse_constant_spec( $fh ); 


# Parse a constant spec file. 
# Pass in a handle to process. 
# As long as it acts like a file handle, it will work. 
sub parse_constant_spec { 
    my $fh = shift; 

    my %spec; 

    # Until file is done: 
        # Read in a whole block 
    while( my $block = read_block($fh) ) { 

        # Parse the and return key/value pairs for a hash. 
        my %constant = parse_block( $block ); 

        # Store a ref to the hash in a big hash of all blocks, keyed by constant_name. 
        $spec{ $constant{const_name} } = \%constant; 

    } 

    # Return ref to big hash with all block data 
    return \%spec; 
} 

# Read a constant definition block from a file handle. 
# void return when there is no data left in the file. 
# Otherwise return an array ref containing lines to in the block.  
sub read_block { 
    my $fh = shift; 

    my @lines; 
    my $block_started = 0; 

    while( my $line = <$fh> ) { 

        $block_started++ if $line =~ /^constant/; 

        if( $block_started ) { 

            last if $line =~ /^\s*$/; 

            push @lines, $line; 
        } 
    } 

    return \@lines if @lines; 

    return; 
} 


sub parse_block { 
    my $block = shift; 
    my ($start_line, @attribs) = @$block; 

    my %constant; 

    # Break down first line: 
    # First separate assignment from option list. 
    my ($start_head, $start_tail) = split /=/, $start_line; 

    # work on option list 
    my @options = split /\s+/, $start_head; 

    # Recover constant_name from options: 
    $constant{const_name} = pop @options; 
    $constant{options} = \@options; 

    # Now we parse the value/type specifier 
    @constant{'type', 'value' } = parse_type_value_specifier( $start_tail ); 

    # Parse attribute lines. 
    # since we've already got multiple per line, get them all at once. 
    chomp @attribs; 
    my $attribs = join ' ', @attribs; 

    #  we have one long line of mixed key = "value" or key = <TYPE VALUE>  

    @attribs = $attribs =~ /\s*(\w+\s+=\s+\w+\s+|\w+\s+=\s+".*?"|\w+\s+=\s+<.*?>)\s*/g; 

    for my $attrib ( @attribs ) { 
        warn "$attrib\n"; 
        my ($name, $value) = split /\s*=\s*/, $attrib; 

        if( $value =~ /^"/ ) {  
            $value =~ s/^"|"\s*$//g; 
        } 
        elsif( $value =~ /^</ ) { 
           $value = [ parse_type_value_specifier( $start_tail ) ]; 
        } 
        else { 
            warn "Bad line"; 
        } 

        $constant{ $name } = $value; 
    } 

    return %constant; 
} 

sub parse_type_value_specifier { 
    my $tvs = shift; 

    my ($type, $value) = $tvs =~ /<(\w+)\s+(.*?)>/; 

    return $type, $value; 
} 

__DATA__ 
constant fixup GemEstabCommDelay = <U2 20> 
    vid = 6 
    name = "ESTABLISHCOMMUNICATIONSTIMEOUT" 
    units = "s" 
    min = <U2 0> 
    max = <U2 1800> 
    default = <U2 20> 


constant fixup private GemConstantFileName = <A "C:\\TMP\\CONST.LOG"> 
    vid = 4 
    name = ""  units = "" 


constant fixup private GemAlarmFileName = <A "C:\\TMP\\ALARM.LOG"> 
    vid = 0 
    name = "" 
    units = ""   

Output:

D:\learning\perl>hello1.pl
vid = 6
Bad line at D:\learning\perl\hello1.pl line 102, <DATA> line 8.
name = "ESTABLISHCOMMUNICATIONSTIMEOUT"
units = "s"
min = <U2 0>
max = <U2 1800>
default = <U2 20>
vid = 4
Bad line at D:\learning\perl\hello1.pl line 102, <DATA> line 13.
name = ""
units = ""
vid = 0
Bad line at D:\learning\perl\hello1.pl line 102, <DATA> line 18.
name = ""
units = ""
$VAR1 = {
          'GemAlarmFileName' => {
                                  'vid' => '0      ',
                                  'options' => [
                                                 'constant',
                                                 'fixup',
                                                 'private'
                                               ],
                                  'value' => '"C:\\\\TMP\\\\ALARM.LOG"',
                                  'name' => '',
                                  'type' => 'A',
                                  'const_name' => 'GemAlarmFileName',
                                  'units' => ''
                                },
          'GemEstabCommDelay' => {
                                   'vid' => '6      ',
                                   'options' => [
                                                  'constant',
                                                  'fixup'
                                                ],
                                   'value' => '20',
                                   'min' => [
                                              'U2',
                                              '20'
                                            ],
                                   'name' => 'ESTABLISHCOMMUNICATIONSTIMEOUT',
                                   'max' => [
                                              'U2',
                                              '20'
                                            ],
                                   'default' => [
                                                  'U2',
                                                  '20'
                                                ],
                                   'type' => 'U2',
                                   'units' => 's',
                                   'const_name' => 'GemEstabCommDelay'
                                 },
          'GemConstantFileName' => {
                                     'vid' => '4      ',
                                     'options' => [
                                                    'constant',
                                                    'fixup',
                                                    'private'
                                                  ],
                                     'value' => '"C:\\\\TMP\\\\CONST.LOG"',
                                     'name' => '',
                                     'type' => 'A',
                                     'const_name' => 'GemConstantFileName',
                                     'units' => ''
                                   }
        };

D:\learning\perl>

You could notice that 'vid' => '0 ', (notice the white space)

The code above from the answer. I am studying it. :-)

Thank you.

Answer 1

$myString =~ s/^\s*(.*)\s*$/$1/;

This will trim whitespace from both sides.

from just the right:

$myString =~ s/\s*$//;

Answer 2

sub trim($)
{
    my $string = shift;
    $string =~ s/^\s+//;
    $string =~ s/\s+$//;
    return $string;
}


print trim($myString)

Answer 3

Try this:

# Delete leading/trailing whitespace.
$string =~ s/^\s+|\s+$//g;

Answer 4

If your white space is just spaces, then the following code will remove all spaces:

$mystring =~ tr/ //ds;

Answer 5

sub trim
{
    my $str = $_[0];
    $str=~s/^\s+|\s+$//g;
    return $str;
}

print trim(" 4 ");

Answer 6

Another potential alternative solution is Text::Trim from CPAN, which will "remove leading and/or trailing whitespace from strings". It has a trim function which may suit your needs.

Answer 7

Hello Nano HE

Just looking over your program, I found 3 spots that could be improved or fixed.

I apologize if my code doesn't format well. :-(

In your function parse_block(...), there are 3 items that need attention.

@attribs = $attribs =~ /\s*(\w+\s+=\s+\w+\s+|\w+\s+=\s+".*?"|\w+\s+=\s+<.*?>)\s*/g;

To eliminate the white space after vid => '6 ', just don't include the \s+ at the end of your first sub-regex.

Write it as:

@attribs = $attribs =~ /\s*(\w+\s+=\s+\w+|\w+\s+=\s+".*?"|\w+\s+=\s+<.*?>)\s*/g;  

$value = [ parse_type_value_specifier( $start_tail ) ];  

You want this instead:

$value = [ parse_type_value_specifier( $value ) ]; 

(Note that the parameter to the function should be $value and not $start_tail.) You probably didn't notice this.

In the loop for @attributes, the 'else' in the if/else condition excutes when the 'value' has a plain value, (no "" or <...> items in 'value').

Update: Changed parameter in

parse_type_value_specifier(...)

to $value. It was (incorrectly) stated as $attrib.