line-driver

A simple configurable module to read or write files line by line.

Install

npm install line-driver

or

npm install -g line-driver

Usage

Since the module usage is pretty straightforward, let's jump right into examples.

Not everything is covered in these Examples, so jump down to API to get the full information.

First, import the module into your program:

var LineDriver = require('line-driver');

For all of the examples, let's pretend that example.txt consists of the following:

1|  one
2|  two
3|  three
4|  four
5|  five

---

Reading a file

Simple Example

LineDriver.read( {
  in : 'path/to/example.txt',
  line : function( props, parser ){
    console.log( parser.line );
  }
} );

• line - The function to be called every time the Parser encounters a new line
  • props - The object that contains the Settings or Properties used by the Parser
    • The exact same props object is sent to every function call and can be used to share data from one function to another
    • Changing any settings in this object will not have any effect
  • parser - The object that allows the function to interact with the state of the Parser
    • parser.line - The line that the parser is currently handling
    • This object has more attributes/properties, some of which are only available in certain contexts. Please read the API documentation to learn more.
• in - The path to the file to be read (using fs.readFile)
  • This path can also be an web address starting with 'http://' or 'https://'

In this scenario, every line from the file will be captured and printed to the console:

one
two
three
four
five
>

---

Line Index Exclusion

There are five input properties that define which lines are sent to the line function that can be used independently from or in conjunction with each other.

• first - The index of the first line to capture
  • Default : 1
• last - The index of the last line to capture
• count - How many total lines to capture
• range - An array of the [first, last] values
• step - Spacing betweens captured lines
  • Default : 1

Note - There is an additional settings called absolute, which defines whether these indices refer to the 'absolute line index' or the 'valid line index'

• Default : false ('valid line index')
• See here for examples of Absolute vs Relative

---

• first

LineDriver.read( {
  in : 'path/to/example.txt',
  line : function( props, parser ){
    console.log( parser.line );
  },
  props : {
    first : 2
  }
} );

Every line starting from line 2 will be captured:

two
three
four
five
>

---

• last

LineDriver.read( {
  in : 'path/to/example.txt',
  line : function( props, parser ){
    console.log( parser.line );
  },
  props : {
    last : 4
  }
} );

Every line up to and including line 4 will be captured:

one
two
three
four
>

---

• count

LineDriver.read( {
  in : 'path/to/example.txt',
  line : function( props, parser ){
    console.log( parser.line );
  },
  props : {
    first : 2,
    count : 3
  }
} );

Only 3 lines will be captured, starting from line 2:

two
three
four
>

---

• range

LineDriver.read( {
  in : 'path/to/example.txt',
  line : function( props, parser ){
    console.log( parser.line );
  },
  props : {
    range : [2,4]
  }
} );

Only lines 2-4 will be captured:

two
three
four
>

You can also use an array of ranges:

LineDriver.read( {
  in : 'path/to/example.txt',
  line : function( props, parser ){
    console.log( parser.line );
  },
  props : {
    range : [[1,3],[3,5]]
  }
} );

The ranges are processed sequentially:

one
two
three
three
four
five
>

Note - init and close is still only run once

• step

LineDriver.read( {
  in : 'path/to/example.txt',
  line : function( props, parser ){
    console.log( parser.line );
  },
  props : {
    step : 2
  }
} );

Every other line will be captured:

one
three
five
>

---

String Exclusion

There are two input functions that can access parser.line before it gets sent to the line function.

• valid - The function to determine if the parser.line is valid or not.
  • Note - An invalid line will not be sent to the line function
• clean - The function to modify the parser.line before sending for validation

---

valid

LineDriver.read( {
  in : 'path/to/example.txt',
  line : function( props, parser ){
    console.log( parser.line );
  },
  valid : function( props, parser ){
    parser.valid = parser.line.length > 3;
  }
} );

• parser.valid - Determines whether the current line is a valid line or not.

Note - parser.line in this context is only a copy. Modifying it will have no effect.

Only lines where the the parser.line is longer than three characters will be captured:

three
four
five
>

---

clean

LineDriver.read( {
  in : 'path/to/example.txt',
  line : function( props, parser ){
    console.log( parser.line );
  },
  clean : function( props, parser ){
    parser.line = parser.line.slice(1);
  },
  valid : function( props, parser ){
    parser.valid = parser.line.length > 3;
  }
} );

Only lines where the the clean-ed parser.line is longer than three characters will be captured:

hree
>

---

There are also three input properties that can allow for automatic cleaning and validation of parser.line

• commentDelim - The character which indicates the start of a comment
  • Default : ''
• trim - Whether or not surrounding whitespace should be removed from the string
  • Default : false
• ignoreEmpty - Whether or not empty strings ('') should be be considered invalid
  • Default : false

In the following example, let's assume that that example.txt now looks like the following:

1|  one
2|
3|  two    #comment?
4|    three
5|  four
6|  #another comment:
7|  five

Now let's use the above properties:

LineDriver.read( {
  in : 'path/to/example.txt',
  line : function( props, parser ){
    console.log( parser.line );
  },
  props : {
    commentDelim : '#',
    trim : true,
    ignoreEmpty : true
  }
} );

What happens behind the scenes?

First, before any clean-ing occurs, the parser does equivalent of the following:

if( props.commentDelim ) parser.line = parser.line.split( props.commentDelim )[0];
if( props.trim ) parser.line.trim();

Then, before any valid-ation occurs, the parser does equivalent of the following:

if( props.ignoreEmpty && !parser.line ) parser.valid = false;

And finally, our captured lines look like this:

one
two
three
four
five
>

---

Absolute vs Valid Lines

There are two methods of excluding lines based on the index, using the absolute line index or using the valid line index.

• Denoted by the absolute property

Below are examples of different properties (using the same messy file and line validation as above) and what they will produce:

Using first:

---

props : {
  first : 3,
  absolute : true
}

Every line starting from line 3 will be checked for validation

two
three
four
five
>

---

Using last:

props : {
  last : 3,
  absolute : true
}

Every line up to and including line 3 will be checked for validation

one
two
>

---

Using step:

props : {
  step : 2,
  absolute : true
}

Every other line will be checked for validation:

one
two
four
five
>

---

Closing a File

A Parser can be forced to close by running the parser.close() function.

LineDriver.read( {
  in : 'path/to/example.txt',
  line : function( props, parser ){
    console.log( parser.line );
    if( parser.line === 'three' ) parser.close();
  }
} );

• parser.close - The function to stop parsing lines and call the close and write functions (if applicable)

Every line will be captured until the parser.close() function is called

one
two
three
>

Running this will stop all line parsing, and call the input close function (and write the out file, if applicable).

---

Other Functions

There are three more input functions:

• init - The function to run once the in file is loaded but before the file parsing begins
• close - The function to run once the in file is done being parsed
• write - The function to run once the out file has been written
  • Note - This is only used by LineDriver.write

Let's again assume that example.txt is back to its original state.

LineDriver.read( {
  in : 'path/to/example.txt',
  init : function( props, parser ){
    console.log('Parsing Started...');
  },
  line : function( props, parser ){
    console.log( '\t' + parser.line );
  },
  close : function( props, parser ){
    console.log('...Parsing Finished');
  }
} );

And the console will look like this:

Parsing Started...
  one
  two
  three
  four
  five
...Parsing Finished
>

---

Other Properties

There are five more input properties:

• sync - Whether or not to use fs.readFileSync & fs.writeFileSync instead of fs.readFile & fs.writeFile
  • Default : false
• encoding - The encoding of the in and out files
  • Default : 'utf8'
• delimiter - The String or RegExp to apply to split the in file into an array of lines.
  • Default : new RegExp('\r\n?|\r?\n')
• join - The String to use to join every line in the out file before writing.
  • Default : '\n'
• eof - The String to add to the end of the file (attached to the last line)
  • Default : ''

---

Writing a file

Example

LineDriver.write( {
  in : 'path/to/example.txt',
  out : 'path/to/new/file.txt',
  line : function( props, parser ){
    parser.write( parser.line );
  }
} );

The only difference between reading and writing a file is the out property and the parser.write function.

• out - The path to the file to be written (using fs.writeFile)
  • Optional - If no out path is given, it write back to the in path
• parser.write - The function to add a line to the out file. Input can be a string or array of strings
  • Note - parser.write still exists for LineDriver.read(), but it will not do anything.

Settings

Every props attribute listed above (except in, out, last and count) have a default value associated with them. These default values can be changed.

Let's assume that our program will only be parsing files that look like this:

1|    one  :  1  ,  two  :  2  ,  three  :  3  ,  four  :  4  ,  five  :  5  

If we only wanted to capture the keys from these files, then the default settings can be updated as follows:

LineDriver.settings( {
  commentDelim : ':',
  trim : true,
  ignoreEmpty : true,
  delimiter : ','
} );

---

Templates

Read about Templates in the API section, here

API

---

Settings

The LineDriver module has default settings associated with it. These default settings can be updated to your preference.

LineDriver.settings( { opts } )

The input options are key : value pairs where:

• key - The name of the setting to update
• value - The value to set as default

The default settings and values are:

• commentDelim - The character which indicates the start of a comment
  • Default : ''
• delimiter - The String or RegExp to apply to split the in file into an array of lines.
  • Default : new RegExp('\r\n?|\r?\n')
• encoding - The encoding of the in and out files
  • Default : 'utf8'
• eof - The String to add to the end of the file (attached to the last line)
  • Default : ''
• absolute - Whether the Line Index Exclusion calculations use the 'absolute line index' or the 'valid line index'
  • Default : false
• first - The index of the first line to capture
  • Default : 1
• ignoreEmpty - Whether or not empty strings ('') should be be considered invalid
  • Default : false
• join - The String to use to join every line in the out file before writing.
  • Default : '\n'
• step - Spacing betweens captured lines
  • Default : 1
• sync - Whether or not to use fs.readFileSync & fs.writeFileSync instead of fs.readFile & fs.writeFile
  • Default : false
• trim - Whether or not surrounding whitespace should be removed from the string
  • Default : false
• maxRedirects - The number of redirects (when reading from an http/https source) before failing
  • Default : 5

---

Reading and Writing

The LineDriver module can read or write a file using the following:

LineDriver.read( { opts } )

or

LineDriver.write( { opts } )

The input options are one or more of the following:

• Properties
• Functions
• Templates
• Paths

Here is a simple example:

In this example:

• line is one of the possible input Functions
• props is the input Properties object

LineDriver.read( {
  in : 'path/to/example.txt',
  line : function( props, parser ){
    console.log( parser.line );
  }
} );

---

Paths

There are two different path objects that the parser recognizes:

• in - The path to the file to be read (using fs.readFile)
  • Required
  • This path can also be an web address starting with 'http://' or 'https://'
• out - The path to the file to be written (using fs.writeFile)
  • Optional - default = in path
  • This is only used by LineDriver.write

Note - The number of acceptable redirects can be set using the maxRedirects property (see above)

---

Functions

There are six functions that the Parser recognizes and handles:

• init - The function to run once the in file is loaded but before the file parsing begins
• clean - The function to modify the parser.line before sending for validation
• valid - The function to determine if the parser.line is valid or not.
  • An invalid line will not be sent to the line function
• line - The function to be called every time the Parser encounters a new line
• close - The function to run once the in file is done being parsed
• write - The function to run once the out file has been written
  • This is only used by LineDriver.write

Every function has two inputs to it:

• props - The object that contains the Settings/Properties used by the Parser
  • It also includes any additional data that was stored in the input Properties object
  • The exact same props object is sent to every function call and can be used to share data from one function to another
  • Changing any settings in this object will not have any effect
• parser -The object that allows the function to interact with the state of the Parser
  • Some parser properties are only available in certain contexts. (See below)

---

• init

The parser object has the following attributes:

• write - The function to add a line to the out file. Input can be a string or array of strings
  • This is only used by LineDriver.write

  init : function( props, parser ){
    console.log('Began parsing the file.');
    parser.write('Start of File');
  }

---

• clean

The parser object has the following attributes:

• line - The line that the parser is currently handling
• index - The object containing the index of the current line
  • absolute - The index of the current line from the start of the file, including invalid lines
  • valid - The index of the previous valid line from the first valid line, excluding invalid lines

  clean : function( props, parser ){
    //to make sure every line is lowercase
    parser.line = parser.line.toLowerCase();
  }

---

• valid

The parser object has the following attributes:

• line - The line that the parser is currently handling
• valid - Determines whether the current line is a valid line or not.
• index - The object containing the index of the current line
  • absolute - The index of the current line from the start of the file, including invalid lines
  • valid - The index of the previous valid line from the first valid line, excluding invalid lines

Notes:

• In this context, line is a copy of the actual line; modifying it will have no effect
• An invalid line will not be sent to the line function

  valid : function( props, parser ){
    //to ignore lines that are three characters or less
    parser.valid = parser.line.length > 3;
  }

---

• line

The parser object has the following attributes:

• line - The line that the parser is currently handling
• index - The object containing the index of the current line
  • absolute - The index of the current line from the start of the file, including invalid lines
  • valid - The index of the current_ line from the first valid line, excluding invalid lines
• close - The function to stop parsing lines and call the close and write functions (if applicable)
• hasNextLine - The function to see if there are any valid lines left in the file
  • Arguments:
    • count - Number of valid lines to check for
      • Optional, default = step Property
• goToLine - The function to capture the next valid line
  • Arguments:
    1. count - Spacing between current line and desired line
    • Optional, default = step Property
    1. ignoreValid - Should the desired line not increase the valid line index?
    • Optional, default = false
• nextLine - The next line in the file
  • Invoking this will update the line and index values to represent the next line
  • Since this internally updates the current line, the parser will not send that line to the line function on the next pass
• write - The function to add a line to the out file. Input can be a string or array of strings
  • This is only used by LineDriver.write

  line : function( props, parser ){
    console.log('Line : ' + parser.line);
    
    if( parser.hasNextLine() ){
      console.log('Next Line : ' + parser.nextLine);
      //parser.line has been updated to the new line since we accessed parser.nextLine
      console.log('Line -> Next Line : ' + parser.line);
    }
    
    if( parser.line === 'thats all folks' ) parser.close();
  }

---

• close

The parser object has the following attributes:

• write - The function to add a line to the out file. Input can be a string or array of strings
  • This is only used by LineDriver.write

  close : function( props, parser ){
    console.log('Done parsing the file.');
    parser.write('End of file');
  }

---

• write

  write : function( props, parser ){
    console.log('Done writing the file.');
  }

---

Properties

The properties are any settings which you would like to override the default value of.

In additional to the settings listed above, the Parser can recognize these additional settings:

• last - The index of the last line to capture
• count - How many total lines to capture

Note - Any additional data can be attached to the properties object and can be shared

---

Templates

Templates can be used to create default values for properties or functions.

Let's create a template for parsing .csv files and assume that example.txt looks like the following:

1|  ,X,Y
2|  X,XX,XY
3|  X,XX,XY

Let's assume we want to create a template that parses the above table, and then only sends the 'cells' to the line function

LineDriver.template('table', {
  //use the props object to store data
  init : function( next, props, parser ){
    props.table = [];
    props.titles = {
      rows : [],
      cols : []
    };
    next();
  },
  line : function( next, props, parser ){
    //turn the row into an array of cells
    var rowTitle,
      row = parser.line.split(',');
    
    //the first cell contains the row title
    rowTitle = row.splice(0,1)[0];
    
    //the first row contains the column titles
    if( parser.index.valid === 1 ) props.titles.cols = row;
    else{
      props.titles.rows.push( rowTitle );
      //send each cell to the line function
      row.forEach(function( value, i ){
        props.currentCell = {
          value : value,
          col : i,
          row : parser.index.valid - 1
        };
        next();
      });
    }
  }
} );

• next - The function to call the corresponding function from the original input
  • i.e. : Running next() in the line function will called the input line function
• parser.index - The object containing the index of the current line
  • absolute - The index of the current line from the start of the file, including invalid lines
  • valid - The index of the current line from the first valid line, excluding invalid lines

Now let's use that template:

LineDriver.read({
  in : 'path/to/example.txt',
  line : function(args, parser){
    var value = props.currentCell.value,
      colTitle = props.titles.cols[props.currentCell.row],
      rowTitle = props.titles.rows[props.currentCell.col];
      
    console.log( rowTitle + ' + ' + colTitle + ' = ' + value );
  },
  template : ['table']
})

• template - An array of names of templates to use when parsing the in file.
  • Note - If more than one template name exists, the next() function will called the corresponding function in the next template in the list
  • The first template called is index 0
    • Once no more templates exist, then the corresponding input function will be called

Running the above function and template will produce a console that looks like the following:

X + X = XX
X + Y = XY
X + X = XX
X + Y = XY
>

Useful for genetics, not for algebra.

Note - The 'default' template, if it exists, will be automatically applied as the first template unless it already appears in the input template list.

Templates give you some freedom on how data gets sent to the final function. For example, the above row.forEach() function can look like the following:

//send each cell to the line function
row.forEach(function( value, i ){
  props.handleCell(value, props.titles.cols[i], rowTitle);
});

And it can be used in the following manner:

LineDriver.read({
  in : 'path/to/example.txt',
  props : {
    handleCell : function(value, colTitle, rowTitle){
      console.log( rowTitle + ' + ' + colTitle + ' = ' + value );
    }
  },
  template : ['table']
})

License

MIT