pad

Pad a string.

Usage

var pad = require( '@stdlib/string/pad' );

pad( str, len[, options] )

Pads a string such that the padded string has a length of len.

var str = pad( 'a', 5 );
// returns 'a    '

The function accepts the following options:

  • lpad: string used to left pad. Default: ''.
  • rpad: string used to right pad. Default: ' '.
  • centerRight: boolean indicating whether to center right in the event of a tie. Default: false (i.e., center left).

By default, an input string is padded with spaces. To pad with a different character or sequence of characters, provide a pad string.

var str = pad( 'a', 10, {
    'lpad': 'b'
});
// returns 'bbbbbbbbba'

str = pad( 'a', 12, {
    'rpad': 'b'
});
// returns 'abbbbbbbbbbb'

To center an input string, provide both lpad and rpad options.

var opts = {
    'lpad': 'a',
    'rpad': 'c'
};

var str = pad( 'b', 11, opts );
// returns 'aaaaabccccc'

When both lpad and rpad are specified and len-str.length is odd, left and right padding cannot equally split the available padding space. By default, right padding receives the extra character (i.e., the input string is left-centered).

var opts = {
    'lpad': 'a',
    'rpad': 'c'
};

var str = pad( 'b', 10, opts );
// returns 'aaaabccccc'

To center right, set the centerRight option.

var opts = {
    'lpad': 'a',
    'rpad': 'c',
    'centerRight': true
};

var str = pad( 'b', 10, opts );
// returns 'aaaaabcccc'

Notes

  • In contrast to lpad and rpad, any padding which does not evenly divide available space is trimmed such that the returned string length is always len.

    var opts = {
        'lpad': 'boop',
        'rpad': 'woot'
    };
    var str = pad( 'beep', 10, opts );
    // returns 'boobeepwoo'
    
  • Similarly, if len < str.length, the input string is trimmed.

    // Pad right, trim right:
    var str = pad( 'beep', 2 );
    // returns 'be'
    
    // Pad left, trim left:
    str = pad( 'beep', 2, {
        'lpad': 'b'
    });
    // returns 'ep'
    
    // Pad both, trim both:
    str = pad( 'beep', 2, {
        'lpad': '@',
        'rpad': '!'
    });
    // returns 'ee'
    
    // Pad both, trim both starting from left:
    str = pad( 'abcdef', 3, {
        'lpad': '@',
        'rpad': '!'
    });
    // returns 'cde'
    
    // Pad both, trim both starting from right:
    str = pad( 'abcdef', 3, {
        'lpad': '@',
        'rpad': '!',
        'centerRight': true
    });
    // returns 'bcd'
    

Examples

var round = require( '@stdlib/math/base/special/round' );
var randu = require( '@stdlib/random/base/randu' );
var pad = require( '@stdlib/string/pad' );

var str = 'boop';
var out;
var len;
var i;

for ( i = 0; i < 100; i++ ) {
    len = round( randu()*10.0 ) + str.length;
    out = pad( str, len, {
        'lpad': 'beep',
        'rpad': 'p'
    });
    console.log( '%s. %d. %d.', out, len, out.length );
}

CLI

Usage

Usage: padstr [options] [<string>] --len <length>

Options:

  -h,    --help                Print this message.
  -V,    --version             Print the package version.
         --len length          String length.
         --lpad str            String used to left pad. Default: ''.
         --rpad str            String used to right pad. Default: ' '.
         --cright              Center right in the event of a tie.

Examples

$ padstr beep --len 10 --lpad b --rpad p
bbbbeepppp

To use as a standard stream,

$ echo -n 'beep' | pad --len 9 --lpad a --rpad o
aabeepoo0