Hacker News Reader

Comment by motters | Hacker News Reader

That's the thing about unix-like systems. No matter how much you have learned there's always some command you don't know.

View on HN

paste was my most recent "holy shit this saves so much time" discovery. I blame it on the not quite intuitive name.

What do you use it for?

One use is converting columns of numbers into math strings for bc.

Example (contrived):

    $ seq 10 20 | paste -s -d +
    10+11+12+13+14+15+16+17+18+19+20

    $ seq 10 20 | paste -s -d + | bc
    165

Or converting columns of strings into regex 'or' clauses for searching (contrived example again):

    $ cut -f 3 -d , something.csv | paste -s -d "|"
    a|b|c|d|e|f

    $ egrep "$(cut -f 3 -d , something.csv | paste -s -d "|")" another_file
    ... result lines appear here ...

ahah, so that's where R's paste() function comes from...

seq has the -s flag which voids the need of the paste for that command:

  $ seq -s + 10 20
  10+11+12+13+14+15+16+17+18+19+20

But I agree that the paste is very useful.

  # a few random samples for an IN SQL statement
  $ shuf -i 1-500000 -n 5 | paste -s -d ,
  371492,250061,266669,455846,295852

  # we can even get PI
  $ ( seq -s + -f '4/%g' 1 4 100000 && seq -s - -f '4/%g' 3 4 100000 ) | paste -s -d - | bc -l
  3.14157265358979523735

There is a faster way to get pi in bc:

  echo '4*a(1)' | bc -l

(That is, 4×arctan(1)=4×π/4=π.) But your way is truly an awesome use of Unix!

I've used paste all my life, but I never knew you could do

  paste - -

to convert stdin into 2 columns (or "paste - - - -" to get 4 columns!). TIL ...

Together with cut to parse CSV files and e.g. convert a text column into a row.

Reply on news.ycombinator.com