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pad

Pad a string.

Installation

npm install @stdlib/string-pad

Alternatively,

• To load the package in a website via a script tag without installation and bundlers, use the ES Module available on the esm branch (see README).
• If you are using Deno, visit the deno branch (see README for usage intructions).
• For use in Observable, or in browser/node environments, use the Universal Module Definition (UMD) build available on the umd branch (see README).
• To use as a general utility for the command line, install the corresponding CLI package globally.

The branches.md file summarizes the available branches and displays a diagram illustrating their relationships.

To view installation and usage instructions specific to each branch build, be sure to explicitly navigate to the respective README files on each branch, as linked to above.

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 );
}

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CLI

Installation

To use as a general utility, install the CLI package globally

npm install -g @stdlib/string-pad-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.
         --split sep           Delimiter for stdin data. Default: '/\\r?\\n/'.

Notes

• If the split separator is a regular expression, ensure that the split option is either properly escaped or enclosed in quotes.

  # Not escaped...
  $ echo -n $'beep\nboop' | padstr --len 10 --split /\r?\n/
  
  # Escaped...
  $ echo -n $'beep\nboop' | padstr --len 10 --split /\\r?\\n/

• The implementation ignores trailing delimiters.

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
aabeepooo

By default, when used as a standard stream, the implementation assumes newline-delimited data. To specify an alternative delimiter, set the split option.

$ echo -n 'beep\tboop' | pad --len 9 --lpad a --rpad o --split '\t'
aabeepooo
aaboopooo

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See Also

• @stdlib/string-left-pad: left pad a string.
• @stdlib/string-right-pad: right pad a string.

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Notice

This package is part of stdlib, a standard library for JavaScript and Node.js, with an emphasis on numerical and scientific computing. The library provides a collection of robust, high performance libraries for mathematics, statistics, streams, utilities, and more.

For more information on the project, filing bug reports and feature requests, and guidance on how to develop stdlib, see the main project repository.

Community

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License

See LICENSE.

Copyright

Copyright © 2016-2024. The Stdlib Authors.