London | 26-SDC-July | Raihan Sharif | Sprint 4 | implement shell tools python

[RaihanSharif]

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Changelist

Implemented cat, ls, wc.

Task code: CYF-1152

[SlideGauge]

Good job, I left several comments, could you fix them please?

[SlideGauge]

Each flag is declared action="store_true", default="l" (and "w", "c"). With store_true, when the flag is
absent the value falls back to that default string - and a non-empty string is truthy. So run wc -l
sample-files/3.txt: does it print only the line count, or all three? What should default be for a boolean flag so
that "flag not given" reads as false?

[RaihanSharif]

...uh, yeah, that's bad.

I've now added a check that if no flags are supplied, then just set them all to true.
Which then means that wc prints the lines, word count, and bytes of the files.

Otherwise, the flags are processed individually, so that any combination of the three will work.

[SlideGauge]

format_lines numbers with enumerate(..., start=1) and is called fresh for each file in cat_file. Run cat -n
sample-files/*.txt against the real cat - does the count reset to 1 at each file, or keep climbing? Where would the counter need to live to carry across files?

[RaihanSharif]

yes, the numbering starts from 1 for each file in the cat input

cat -n sample-files/*
     1  Once upon a time...
     1  There was a house made of gingerbread.
     1  It looked delicious.
     2  I was tempted to take a bite of it.
     3  But this seemed like a bad idea...
     4
     5  There's more to come, though...

python cat:

python3 cat.py -n sample-files/*
     1  Once upon a time...
     1  There was a house made of gingerbread.
     1  It looked delicious.
     2  I was tempted to take a bite of it.
     3  But this seemed like a bad idea...
     4
     5  There's more to come, though...

You asked this in the nodeJS version of cat as well. Are you hinting at something, and I'm just not getting it?

[SlideGauge]

lines[-1] == "" - but readlines() keeps the trailing \n, so an element is "\n", never "". Does this pop ever
actually run? Check wc -l against real wc on a file that does and doesn't end in a newline.

[RaihanSharif]

Thank you for pointing that out, I 'translated' my js code too literally without accounting for how readlines() or how wc actually counts lines.

wc counts the number of '\n' characters, not necessarily non-empty lines. Last empty line is excluded because it doesn't have a '\n' in it.

I've changed my implementation to just read the file, and count the number of '\n' characters. The output now matches the real wc.

It also made my -w logic a bit simpler.