Redact

Redact the contents of each line of a file according to rules expressed as JSON. The following sample is from sampleRules.json.

[
  { startingAt:  3, replaceWith: "TTTT" },
  { startingAt: 15, replaceWith: "VVV", padding: 7 }
]

The startingAt index is zero-based. The above means that for for each line of the input file:

• starting at column 4, overwrite content with TTTT
• starting at column 16, overwrite content with VVV . If necessary, pad with extra space so that at least 7 characters are overwritten);
• If the field replacement exceeds the line length, truncate the replacement so that line length is preserved.
• The optional padding attribute means pad to the right with spaces until the string length is the size indicated (according to String.prototype.padEnd()).

Invoke as

node redact sampleRules.json sampleInput.txt > redactedFile.txt

Here is the result run on the sample.

$ cat sampleInput.txt
This is a test file.  We need some long lines.
It is use to test a redaction utility. Good luck.
A short line.
$ node redact sampleRules.json sampleInput.txt
ThiTTTT a teVVV       We need some long lines.
It TTTTse toVVV       daction utility. Good luck.
A sTTTT lineV

Error and warning messages are written to standard error. They will not appear in the result file if standard output is redirected.