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lpad

Left pad a string.

Installation

npm install @stdlib/string-left-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 lpad = require( '@stdlib/string-left-pad' );

lpad( str, len[, pad] )

Left pads a string such that the padded string has a length of at least len.

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

By default, an input string is padded with a Unicode "space" character (U+0020). To pad with a different character or sequence of characters, provide a pad string.

var str = lpad( 'beep', 10, 'b' );
// returns 'bbbbbbbeep'

str = lpad( 'boop', 12, 'beep' );
// returns 'beepbeepboop'

Notes

• An output string is not guaranteed to have a length of exactly len, but to have a length of at least len. To generate a padded string having a length equal to len

  var str = lpad( 'boop', 10, 'beep' ); // => length 12
  // returns 'beepbeepboop'
  
  str = str.substring( str.length-10 ); // => length 10
  // returns 'epbeepboop'

• This function differs from String.prototype.padStart in the following ways:

  • The function is not guaranteed to return a string having a length exactly equal to len (as explained above).
  • The function does not truncate pad (from the end) in order to ensure the returned string has length len.

  To replicate String.prototype.padStart truncation behavior

  var floorb = require( '@stdlib/math-base-special-floorb' );
  
  function padStart( str, len, pad ) {
      var n;
      if ( len <= str.length ) {
          return str;
      }
      n = floorb( len-str.length, 1, pad.length ) + str.length;
      return pad.substring( 0, len-n ) + lpad( str, n, pad );
  }
  
  var str = padStart( 'boop', 10, 'beep' );
  // returns 'bebeepboop'

Examples

var discreteUniform = require( '@stdlib/random-base-discrete-uniform' );
var lpad = require( '@stdlib/string-left-pad' );

var str = 'beep';
var i;
for ( i = 0; i < 100; i++ ) {
    console.log( lpad( str, discreteUniform( str.length, str.length+10 ), 'b' ) );
}

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CLI

Installation

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

npm install -g @stdlib/string-left-pad-cli

Usage

Usage: lpad [options] --len=<length> [<string>]

Options:

  -h,    --help                Print this message.
  -V,    --version             Print the package version.
         --len length          Minimum string length.
         --pad str             String used to pad. Default: ' '.
         --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' | lpad -len 8 --split /\r?\n/
  
  # Escaped...
  $ echo -n $'beep\nboop' | lpad -len 8 --split /\\r?\\n/

• The implementation ignores trailing delimiters.

Examples

$ lpad beep --len 10 --pad b
bbbbbbbeep

To use as a standard stream,

$ echo -n 'beep' | lpad --len 8
    beep

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 'boop\tbeep' |  lpad --len 8 --split '\t'
    boop
    beep

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See Also

• @stdlib/string-pad: 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.