Linux – All possible permutations of words in different files in pairs

command linelinuxpermutationstext processing

I have multiple files, let's say file1, file2 etc. Each file has one word in each line, like:

file1 file2 file3
one   four  six
two   five
three

What I want is to combine them in a new file4 in every possible permutation (without repetition) in pairs. Like

onetwo
onethree
onefour
onefive
...
twothree
...
onefour
...
fourone
...

How is this possible using Linux commands?

Best Answer

Use this:

cat FILE1 FILE2 FILE3 | \
    perl -lne 'BEGIN{@a}{push @a,$_}END{foreach $x(@a){foreach $y(@a){print $x.$y}}}'

Output:

oneone
onetwo
onethree
onefour
onefive
onesix
oneseven
twoone
twotwo
twothree
twofour
twofive
twosix
twoseven
threeone
threetwo
threethree
threefour
threefive
threesix
threeseven
fourone
fourtwo
fourthree
fourfour
fourfive
foursix
fourseven
fiveone
fivetwo
fivethree
fivefour
fivefive
fivesix
fiveseven
sixone
sixtwo
sixthree
sixfour
sixfive
sixsix
sixseven
sevenone
seventwo
seventhree
sevenfour
sevenfive
sevensix
sevenseven

A more advanced example

With some trickery you can get a bit more complicated. Say file3 contains:

6
7
8

You can do (file1 + file3) / file2 like this:

paste -d'(+)/' /dev/null file1 file3 /dev/null file2

Output:

(2+6)/10
(3+7)/100
(4+8)/1000

This works because paste cycles through its delimiter list for each line.

React to divide-by-zero

Illigal operations sent to bc result in a warning being sent to standard error. You could redirect these to a different file and decide program flow based on its content, e.g.:

paste -d/ file1 file2 | bc -l > resultfile 2> errorfile
if grep -q 'Divide by zero' errorfile; then
  echo "Error in calculation"
else
  echo "All is well"
fi

Or if there was any error:

paste -d/ file1 file2 | bc -l > resultfile 2> errorfile
if ! file errorfile | grep -q empty; then
  echo "Error in calculation"
else
  echo "All is well"
fi

Best Answer

Related Solutions

Arithmetic operations between files

A more advanced example

React to divide-by-zero

Related Question