Bash - pair each line of file












10















This question is strongly related to this and this question. I have a file that contains several lines where each line is a path to a file. Now I want to pair each line with each different line (not itself). Also a pair A B is equal to a B A pair for my purposes, so only one of these combinations should be produced.



Example



files.dat reads like this in a shorthand notation, each letter is a file path (absolute or relative)



a
b
c
d
e


Then my result should look something like this:



a b
a c
a d
a e
b c
b d
b e
c d
c e
d e


Preferrably I would like to solve this in bash. Unlike the other questions, my file list is rather small (about 200 lines), so using loops and RAM capacity
pose no problems.










share|improve this question

























  • Does it have to be in bash proper, or just something available via the bash commandline? Other utilities are better positioned to process text.

    – Jeff Schaller
    Mar 17 at 14:15











  • @JeffSchaller Something accessible via the bash commandline. I was a bit unclear, sorry

    – Enno
    Mar 17 at 14:17













  • This is almost becoming a Code Golf :P

    – Richard de Wit
    Mar 18 at 11:22






  • 3





    As a general rule, as long as you need to do something non-trivial, use your favourite scripting language over BASH. It will be less fragile (for example, against special characters or spaces), and much easier to expand whenever you need it (if you need three, or filter some of them away). Python or Perl should be installed in almost any Linux box, so they are good choices (unless you are working on embedded systems, like Busybox).

    – Davidmh
    Mar 18 at 12:26
















10















This question is strongly related to this and this question. I have a file that contains several lines where each line is a path to a file. Now I want to pair each line with each different line (not itself). Also a pair A B is equal to a B A pair for my purposes, so only one of these combinations should be produced.



Example



files.dat reads like this in a shorthand notation, each letter is a file path (absolute or relative)



a
b
c
d
e


Then my result should look something like this:



a b
a c
a d
a e
b c
b d
b e
c d
c e
d e


Preferrably I would like to solve this in bash. Unlike the other questions, my file list is rather small (about 200 lines), so using loops and RAM capacity
pose no problems.










share|improve this question

























  • Does it have to be in bash proper, or just something available via the bash commandline? Other utilities are better positioned to process text.

    – Jeff Schaller
    Mar 17 at 14:15











  • @JeffSchaller Something accessible via the bash commandline. I was a bit unclear, sorry

    – Enno
    Mar 17 at 14:17













  • This is almost becoming a Code Golf :P

    – Richard de Wit
    Mar 18 at 11:22






  • 3





    As a general rule, as long as you need to do something non-trivial, use your favourite scripting language over BASH. It will be less fragile (for example, against special characters or spaces), and much easier to expand whenever you need it (if you need three, or filter some of them away). Python or Perl should be installed in almost any Linux box, so they are good choices (unless you are working on embedded systems, like Busybox).

    – Davidmh
    Mar 18 at 12:26














10












10








10


0






This question is strongly related to this and this question. I have a file that contains several lines where each line is a path to a file. Now I want to pair each line with each different line (not itself). Also a pair A B is equal to a B A pair for my purposes, so only one of these combinations should be produced.



Example



files.dat reads like this in a shorthand notation, each letter is a file path (absolute or relative)



a
b
c
d
e


Then my result should look something like this:



a b
a c
a d
a e
b c
b d
b e
c d
c e
d e


Preferrably I would like to solve this in bash. Unlike the other questions, my file list is rather small (about 200 lines), so using loops and RAM capacity
pose no problems.










share|improve this question
















This question is strongly related to this and this question. I have a file that contains several lines where each line is a path to a file. Now I want to pair each line with each different line (not itself). Also a pair A B is equal to a B A pair for my purposes, so only one of these combinations should be produced.



Example



files.dat reads like this in a shorthand notation, each letter is a file path (absolute or relative)



a
b
c
d
e


Then my result should look something like this:



a b
a c
a d
a e
b c
b d
b e
c d
c e
d e


Preferrably I would like to solve this in bash. Unlike the other questions, my file list is rather small (about 200 lines), so using loops and RAM capacity
pose no problems.







shell-script text-processing






share|improve this question















share|improve this question













share|improve this question




share|improve this question








edited Mar 17 at 14:18









Jeff Schaller

43.8k1161141




43.8k1161141










asked Mar 17 at 14:14









EnnoEnno

1534




1534













  • Does it have to be in bash proper, or just something available via the bash commandline? Other utilities are better positioned to process text.

    – Jeff Schaller
    Mar 17 at 14:15











  • @JeffSchaller Something accessible via the bash commandline. I was a bit unclear, sorry

    – Enno
    Mar 17 at 14:17













  • This is almost becoming a Code Golf :P

    – Richard de Wit
    Mar 18 at 11:22






  • 3





    As a general rule, as long as you need to do something non-trivial, use your favourite scripting language over BASH. It will be less fragile (for example, against special characters or spaces), and much easier to expand whenever you need it (if you need three, or filter some of them away). Python or Perl should be installed in almost any Linux box, so they are good choices (unless you are working on embedded systems, like Busybox).

    – Davidmh
    Mar 18 at 12:26



















  • Does it have to be in bash proper, or just something available via the bash commandline? Other utilities are better positioned to process text.

    – Jeff Schaller
    Mar 17 at 14:15











  • @JeffSchaller Something accessible via the bash commandline. I was a bit unclear, sorry

    – Enno
    Mar 17 at 14:17













  • This is almost becoming a Code Golf :P

    – Richard de Wit
    Mar 18 at 11:22






  • 3





    As a general rule, as long as you need to do something non-trivial, use your favourite scripting language over BASH. It will be less fragile (for example, against special characters or spaces), and much easier to expand whenever you need it (if you need three, or filter some of them away). Python or Perl should be installed in almost any Linux box, so they are good choices (unless you are working on embedded systems, like Busybox).

    – Davidmh
    Mar 18 at 12:26

















Does it have to be in bash proper, or just something available via the bash commandline? Other utilities are better positioned to process text.

– Jeff Schaller
Mar 17 at 14:15





Does it have to be in bash proper, or just something available via the bash commandline? Other utilities are better positioned to process text.

– Jeff Schaller
Mar 17 at 14:15













@JeffSchaller Something accessible via the bash commandline. I was a bit unclear, sorry

– Enno
Mar 17 at 14:17







@JeffSchaller Something accessible via the bash commandline. I was a bit unclear, sorry

– Enno
Mar 17 at 14:17















This is almost becoming a Code Golf :P

– Richard de Wit
Mar 18 at 11:22





This is almost becoming a Code Golf :P

– Richard de Wit
Mar 18 at 11:22




3




3





As a general rule, as long as you need to do something non-trivial, use your favourite scripting language over BASH. It will be less fragile (for example, against special characters or spaces), and much easier to expand whenever you need it (if you need three, or filter some of them away). Python or Perl should be installed in almost any Linux box, so they are good choices (unless you are working on embedded systems, like Busybox).

– Davidmh
Mar 18 at 12:26





As a general rule, as long as you need to do something non-trivial, use your favourite scripting language over BASH. It will be less fragile (for example, against special characters or spaces), and much easier to expand whenever you need it (if you need three, or filter some of them away). Python or Perl should be installed in almost any Linux box, so they are good choices (unless you are working on embedded systems, like Busybox).

– Davidmh
Mar 18 at 12:26










6 Answers
6






active

oldest

votes


















7














Use this command:



awk '{ name[$1]++ }
END { PROCINFO["sorted_in"] = "@ind_str_asc"
for (v1 in name) for (v2 in name) if (v1 < v2) print v1, v2 }
' files.dat


PROCINFO may be a gawk extension. 
If your awk doesn’t support it,
just leave out the PROCINFO["sorted_in"] = "@ind_str_asc" line
and pipe the output into sort (if you want the output sorted).



(This does not require the input to be sorted.)






share|improve this answer































    8














    $ join -j 2 -o 1.1,2.1 file file | awk '!seen[$1,$2]++ && !seen[$2,$1]++'
    a b
    a c
    a d
    a e
    b c
    b d
    b e
    c d
    c e
    d e


    This assumes that no line in the input file contains any whitespace. It also assumes that the file is sorted.



    The join command creates the full cross product of the lines in the file. It does this by joining the file with itself on a non-existing field. The non-standard -j 2 may be replaced by -1 2 -2 2 (but not by -j2 unless you use GNU join).



    The awk command reads the result of this and only outputs results that are pairs that has not yet been seen.






    share|improve this answer


























    • What do you mean by "the file is sorted"? Sorted by which criteria?

      – Enno
      Mar 17 at 14:36











    • @Enno Sorted the way sort -b would sort it. join require sorted input files.

      – Kusalananda
      Mar 17 at 14:44





















    8














    A python solution.
    The input file is fed to itertools.combinations from the standard library, which generates 2-length tuples that are formatted and printed to standard output.



    python3 -c 'from itertools import combinations
    with open("file") as f:
    lines = (line.rstrip() for line in f)
    lines = ("{} {}".format(x, y) for x, y in combinations(lines, 2))
    print(*lines, sep="n")
    '





    share|improve this answer































      6














      If you have ruby installed:



      $ ruby -0777 -F'n' -lane '$F.combination(2) { |c| puts c.join(" ")}' ip.txt
      a b
      a c
      a d
      a e
      b c
      b d
      b e
      c d
      c e
      d e




      • -0777 slurp entire file (should be okay as it is mentioned in OP that file size is small)


      • -F'n' split based on newline, so each line will be an element in $F array


      • $F.combination(2) generate combinations 2 elements at a time


      • { |c| puts c.join(" ")} print as required

      • if input file can contain duplicates, use $F.uniq.combination(2)




      for 3 elements at a time:



      $ ruby -0777 -F'n' -lane '$F.combination(3) { |c| puts c.join(" ")}' ip.txt
      a b c
      a b d
      a b e
      a c d
      a c e
      a d e
      b c d
      b c e
      b d e
      c d e





      With perl (not generic)



      $ perl -0777 -F'n' -lane 'for $i (0..$#F) {
      for $j ($i+1..$#F) {
      print "$F[$i] $F[$j]n" } }' ip.txt
      a b
      a c
      a d
      a e
      b c
      b d
      b e
      c d
      c e
      d e




      With awk



      $ awk '{ a[NR]=$0 }
      END{ for(i=1;i<=NR;i++)
      for(j=i+1;j<=NR;j++)
      print a[i], a[j] }' ip.txt
      a b
      a c
      a d
      a e
      b c
      b d
      b e
      c d
      c e
      d e





      share|improve this answer

































        5














        Here's one in pure shell.



        test $# -gt 1 || exit
        a=$1
        shift
        for f in "$@"
        do
        echo $a $f
        done
        exec /bin/sh $0 "$@"


        Example:



        ~ (137) $ sh test.sh $(cat file.dat)
        a b
        a c
        a d
        a e
        b c
        b d
        b e
        c d
        c e
        d e
        ~ (138) $





        share|improve this answer





















        • 1





          Command substitution strips trailing newlines, so you're better off with something like <file.dat xargs test.sh than test.sh $(cat file.dat)

          – iruvar
          Mar 17 at 20:33



















        1














        Using Perl we can do it as shown:



        $ perl -lne '
        push @A, $_}{
        while ( @A ) {
        my $e = shift @A;
        print "$e $_" for @A;
        }
        ' input.txt





        share|improve this answer























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          6 Answers
          6






          active

          oldest

          votes








          6 Answers
          6






          active

          oldest

          votes









          active

          oldest

          votes






          active

          oldest

          votes









          7














          Use this command:



          awk '{ name[$1]++ }
          END { PROCINFO["sorted_in"] = "@ind_str_asc"
          for (v1 in name) for (v2 in name) if (v1 < v2) print v1, v2 }
          ' files.dat


          PROCINFO may be a gawk extension. 
          If your awk doesn’t support it,
          just leave out the PROCINFO["sorted_in"] = "@ind_str_asc" line
          and pipe the output into sort (if you want the output sorted).



          (This does not require the input to be sorted.)






          share|improve this answer




























            7














            Use this command:



            awk '{ name[$1]++ }
            END { PROCINFO["sorted_in"] = "@ind_str_asc"
            for (v1 in name) for (v2 in name) if (v1 < v2) print v1, v2 }
            ' files.dat


            PROCINFO may be a gawk extension. 
            If your awk doesn’t support it,
            just leave out the PROCINFO["sorted_in"] = "@ind_str_asc" line
            and pipe the output into sort (if you want the output sorted).



            (This does not require the input to be sorted.)






            share|improve this answer


























              7












              7








              7







              Use this command:



              awk '{ name[$1]++ }
              END { PROCINFO["sorted_in"] = "@ind_str_asc"
              for (v1 in name) for (v2 in name) if (v1 < v2) print v1, v2 }
              ' files.dat


              PROCINFO may be a gawk extension. 
              If your awk doesn’t support it,
              just leave out the PROCINFO["sorted_in"] = "@ind_str_asc" line
              and pipe the output into sort (if you want the output sorted).



              (This does not require the input to be sorted.)






              share|improve this answer













              Use this command:



              awk '{ name[$1]++ }
              END { PROCINFO["sorted_in"] = "@ind_str_asc"
              for (v1 in name) for (v2 in name) if (v1 < v2) print v1, v2 }
              ' files.dat


              PROCINFO may be a gawk extension. 
              If your awk doesn’t support it,
              just leave out the PROCINFO["sorted_in"] = "@ind_str_asc" line
              and pipe the output into sort (if you want the output sorted).



              (This does not require the input to be sorted.)







              share|improve this answer












              share|improve this answer



              share|improve this answer










              answered Mar 17 at 14:40









              G-ManG-Man

              13.6k93768




              13.6k93768

























                  8














                  $ join -j 2 -o 1.1,2.1 file file | awk '!seen[$1,$2]++ && !seen[$2,$1]++'
                  a b
                  a c
                  a d
                  a e
                  b c
                  b d
                  b e
                  c d
                  c e
                  d e


                  This assumes that no line in the input file contains any whitespace. It also assumes that the file is sorted.



                  The join command creates the full cross product of the lines in the file. It does this by joining the file with itself on a non-existing field. The non-standard -j 2 may be replaced by -1 2 -2 2 (but not by -j2 unless you use GNU join).



                  The awk command reads the result of this and only outputs results that are pairs that has not yet been seen.






                  share|improve this answer


























                  • What do you mean by "the file is sorted"? Sorted by which criteria?

                    – Enno
                    Mar 17 at 14:36











                  • @Enno Sorted the way sort -b would sort it. join require sorted input files.

                    – Kusalananda
                    Mar 17 at 14:44


















                  8














                  $ join -j 2 -o 1.1,2.1 file file | awk '!seen[$1,$2]++ && !seen[$2,$1]++'
                  a b
                  a c
                  a d
                  a e
                  b c
                  b d
                  b e
                  c d
                  c e
                  d e


                  This assumes that no line in the input file contains any whitespace. It also assumes that the file is sorted.



                  The join command creates the full cross product of the lines in the file. It does this by joining the file with itself on a non-existing field. The non-standard -j 2 may be replaced by -1 2 -2 2 (but not by -j2 unless you use GNU join).



                  The awk command reads the result of this and only outputs results that are pairs that has not yet been seen.






                  share|improve this answer


























                  • What do you mean by "the file is sorted"? Sorted by which criteria?

                    – Enno
                    Mar 17 at 14:36











                  • @Enno Sorted the way sort -b would sort it. join require sorted input files.

                    – Kusalananda
                    Mar 17 at 14:44
















                  8












                  8








                  8







                  $ join -j 2 -o 1.1,2.1 file file | awk '!seen[$1,$2]++ && !seen[$2,$1]++'
                  a b
                  a c
                  a d
                  a e
                  b c
                  b d
                  b e
                  c d
                  c e
                  d e


                  This assumes that no line in the input file contains any whitespace. It also assumes that the file is sorted.



                  The join command creates the full cross product of the lines in the file. It does this by joining the file with itself on a non-existing field. The non-standard -j 2 may be replaced by -1 2 -2 2 (but not by -j2 unless you use GNU join).



                  The awk command reads the result of this and only outputs results that are pairs that has not yet been seen.






                  share|improve this answer















                  $ join -j 2 -o 1.1,2.1 file file | awk '!seen[$1,$2]++ && !seen[$2,$1]++'
                  a b
                  a c
                  a d
                  a e
                  b c
                  b d
                  b e
                  c d
                  c e
                  d e


                  This assumes that no line in the input file contains any whitespace. It also assumes that the file is sorted.



                  The join command creates the full cross product of the lines in the file. It does this by joining the file with itself on a non-existing field. The non-standard -j 2 may be replaced by -1 2 -2 2 (but not by -j2 unless you use GNU join).



                  The awk command reads the result of this and only outputs results that are pairs that has not yet been seen.







                  share|improve this answer














                  share|improve this answer



                  share|improve this answer








                  edited Mar 17 at 14:35

























                  answered Mar 17 at 14:28









                  KusalanandaKusalananda

                  137k17258426




                  137k17258426













                  • What do you mean by "the file is sorted"? Sorted by which criteria?

                    – Enno
                    Mar 17 at 14:36











                  • @Enno Sorted the way sort -b would sort it. join require sorted input files.

                    – Kusalananda
                    Mar 17 at 14:44





















                  • What do you mean by "the file is sorted"? Sorted by which criteria?

                    – Enno
                    Mar 17 at 14:36











                  • @Enno Sorted the way sort -b would sort it. join require sorted input files.

                    – Kusalananda
                    Mar 17 at 14:44



















                  What do you mean by "the file is sorted"? Sorted by which criteria?

                  – Enno
                  Mar 17 at 14:36





                  What do you mean by "the file is sorted"? Sorted by which criteria?

                  – Enno
                  Mar 17 at 14:36













                  @Enno Sorted the way sort -b would sort it. join require sorted input files.

                  – Kusalananda
                  Mar 17 at 14:44







                  @Enno Sorted the way sort -b would sort it. join require sorted input files.

                  – Kusalananda
                  Mar 17 at 14:44













                  8














                  A python solution.
                  The input file is fed to itertools.combinations from the standard library, which generates 2-length tuples that are formatted and printed to standard output.



                  python3 -c 'from itertools import combinations
                  with open("file") as f:
                  lines = (line.rstrip() for line in f)
                  lines = ("{} {}".format(x, y) for x, y in combinations(lines, 2))
                  print(*lines, sep="n")
                  '





                  share|improve this answer




























                    8














                    A python solution.
                    The input file is fed to itertools.combinations from the standard library, which generates 2-length tuples that are formatted and printed to standard output.



                    python3 -c 'from itertools import combinations
                    with open("file") as f:
                    lines = (line.rstrip() for line in f)
                    lines = ("{} {}".format(x, y) for x, y in combinations(lines, 2))
                    print(*lines, sep="n")
                    '





                    share|improve this answer


























                      8












                      8








                      8







                      A python solution.
                      The input file is fed to itertools.combinations from the standard library, which generates 2-length tuples that are formatted and printed to standard output.



                      python3 -c 'from itertools import combinations
                      with open("file") as f:
                      lines = (line.rstrip() for line in f)
                      lines = ("{} {}".format(x, y) for x, y in combinations(lines, 2))
                      print(*lines, sep="n")
                      '





                      share|improve this answer













                      A python solution.
                      The input file is fed to itertools.combinations from the standard library, which generates 2-length tuples that are formatted and printed to standard output.



                      python3 -c 'from itertools import combinations
                      with open("file") as f:
                      lines = (line.rstrip() for line in f)
                      lines = ("{} {}".format(x, y) for x, y in combinations(lines, 2))
                      print(*lines, sep="n")
                      '






                      share|improve this answer












                      share|improve this answer



                      share|improve this answer










                      answered Mar 17 at 15:27









                      iruvariruvar

                      12.2k63062




                      12.2k63062























                          6














                          If you have ruby installed:



                          $ ruby -0777 -F'n' -lane '$F.combination(2) { |c| puts c.join(" ")}' ip.txt
                          a b
                          a c
                          a d
                          a e
                          b c
                          b d
                          b e
                          c d
                          c e
                          d e




                          • -0777 slurp entire file (should be okay as it is mentioned in OP that file size is small)


                          • -F'n' split based on newline, so each line will be an element in $F array


                          • $F.combination(2) generate combinations 2 elements at a time


                          • { |c| puts c.join(" ")} print as required

                          • if input file can contain duplicates, use $F.uniq.combination(2)




                          for 3 elements at a time:



                          $ ruby -0777 -F'n' -lane '$F.combination(3) { |c| puts c.join(" ")}' ip.txt
                          a b c
                          a b d
                          a b e
                          a c d
                          a c e
                          a d e
                          b c d
                          b c e
                          b d e
                          c d e





                          With perl (not generic)



                          $ perl -0777 -F'n' -lane 'for $i (0..$#F) {
                          for $j ($i+1..$#F) {
                          print "$F[$i] $F[$j]n" } }' ip.txt
                          a b
                          a c
                          a d
                          a e
                          b c
                          b d
                          b e
                          c d
                          c e
                          d e




                          With awk



                          $ awk '{ a[NR]=$0 }
                          END{ for(i=1;i<=NR;i++)
                          for(j=i+1;j<=NR;j++)
                          print a[i], a[j] }' ip.txt
                          a b
                          a c
                          a d
                          a e
                          b c
                          b d
                          b e
                          c d
                          c e
                          d e





                          share|improve this answer






























                            6














                            If you have ruby installed:



                            $ ruby -0777 -F'n' -lane '$F.combination(2) { |c| puts c.join(" ")}' ip.txt
                            a b
                            a c
                            a d
                            a e
                            b c
                            b d
                            b e
                            c d
                            c e
                            d e




                            • -0777 slurp entire file (should be okay as it is mentioned in OP that file size is small)


                            • -F'n' split based on newline, so each line will be an element in $F array


                            • $F.combination(2) generate combinations 2 elements at a time


                            • { |c| puts c.join(" ")} print as required

                            • if input file can contain duplicates, use $F.uniq.combination(2)




                            for 3 elements at a time:



                            $ ruby -0777 -F'n' -lane '$F.combination(3) { |c| puts c.join(" ")}' ip.txt
                            a b c
                            a b d
                            a b e
                            a c d
                            a c e
                            a d e
                            b c d
                            b c e
                            b d e
                            c d e





                            With perl (not generic)



                            $ perl -0777 -F'n' -lane 'for $i (0..$#F) {
                            for $j ($i+1..$#F) {
                            print "$F[$i] $F[$j]n" } }' ip.txt
                            a b
                            a c
                            a d
                            a e
                            b c
                            b d
                            b e
                            c d
                            c e
                            d e




                            With awk



                            $ awk '{ a[NR]=$0 }
                            END{ for(i=1;i<=NR;i++)
                            for(j=i+1;j<=NR;j++)
                            print a[i], a[j] }' ip.txt
                            a b
                            a c
                            a d
                            a e
                            b c
                            b d
                            b e
                            c d
                            c e
                            d e





                            share|improve this answer




























                              6












                              6








                              6







                              If you have ruby installed:



                              $ ruby -0777 -F'n' -lane '$F.combination(2) { |c| puts c.join(" ")}' ip.txt
                              a b
                              a c
                              a d
                              a e
                              b c
                              b d
                              b e
                              c d
                              c e
                              d e




                              • -0777 slurp entire file (should be okay as it is mentioned in OP that file size is small)


                              • -F'n' split based on newline, so each line will be an element in $F array


                              • $F.combination(2) generate combinations 2 elements at a time


                              • { |c| puts c.join(" ")} print as required

                              • if input file can contain duplicates, use $F.uniq.combination(2)




                              for 3 elements at a time:



                              $ ruby -0777 -F'n' -lane '$F.combination(3) { |c| puts c.join(" ")}' ip.txt
                              a b c
                              a b d
                              a b e
                              a c d
                              a c e
                              a d e
                              b c d
                              b c e
                              b d e
                              c d e





                              With perl (not generic)



                              $ perl -0777 -F'n' -lane 'for $i (0..$#F) {
                              for $j ($i+1..$#F) {
                              print "$F[$i] $F[$j]n" } }' ip.txt
                              a b
                              a c
                              a d
                              a e
                              b c
                              b d
                              b e
                              c d
                              c e
                              d e




                              With awk



                              $ awk '{ a[NR]=$0 }
                              END{ for(i=1;i<=NR;i++)
                              for(j=i+1;j<=NR;j++)
                              print a[i], a[j] }' ip.txt
                              a b
                              a c
                              a d
                              a e
                              b c
                              b d
                              b e
                              c d
                              c e
                              d e





                              share|improve this answer















                              If you have ruby installed:



                              $ ruby -0777 -F'n' -lane '$F.combination(2) { |c| puts c.join(" ")}' ip.txt
                              a b
                              a c
                              a d
                              a e
                              b c
                              b d
                              b e
                              c d
                              c e
                              d e




                              • -0777 slurp entire file (should be okay as it is mentioned in OP that file size is small)


                              • -F'n' split based on newline, so each line will be an element in $F array


                              • $F.combination(2) generate combinations 2 elements at a time


                              • { |c| puts c.join(" ")} print as required

                              • if input file can contain duplicates, use $F.uniq.combination(2)




                              for 3 elements at a time:



                              $ ruby -0777 -F'n' -lane '$F.combination(3) { |c| puts c.join(" ")}' ip.txt
                              a b c
                              a b d
                              a b e
                              a c d
                              a c e
                              a d e
                              b c d
                              b c e
                              b d e
                              c d e





                              With perl (not generic)



                              $ perl -0777 -F'n' -lane 'for $i (0..$#F) {
                              for $j ($i+1..$#F) {
                              print "$F[$i] $F[$j]n" } }' ip.txt
                              a b
                              a c
                              a d
                              a e
                              b c
                              b d
                              b e
                              c d
                              c e
                              d e




                              With awk



                              $ awk '{ a[NR]=$0 }
                              END{ for(i=1;i<=NR;i++)
                              for(j=i+1;j<=NR;j++)
                              print a[i], a[j] }' ip.txt
                              a b
                              a c
                              a d
                              a e
                              b c
                              b d
                              b e
                              c d
                              c e
                              d e






                              share|improve this answer














                              share|improve this answer



                              share|improve this answer








                              edited Mar 17 at 15:10

























                              answered Mar 17 at 14:43









                              SundeepSundeep

                              7,5511927




                              7,5511927























                                  5














                                  Here's one in pure shell.



                                  test $# -gt 1 || exit
                                  a=$1
                                  shift
                                  for f in "$@"
                                  do
                                  echo $a $f
                                  done
                                  exec /bin/sh $0 "$@"


                                  Example:



                                  ~ (137) $ sh test.sh $(cat file.dat)
                                  a b
                                  a c
                                  a d
                                  a e
                                  b c
                                  b d
                                  b e
                                  c d
                                  c e
                                  d e
                                  ~ (138) $





                                  share|improve this answer





















                                  • 1





                                    Command substitution strips trailing newlines, so you're better off with something like <file.dat xargs test.sh than test.sh $(cat file.dat)

                                    – iruvar
                                    Mar 17 at 20:33
















                                  5














                                  Here's one in pure shell.



                                  test $# -gt 1 || exit
                                  a=$1
                                  shift
                                  for f in "$@"
                                  do
                                  echo $a $f
                                  done
                                  exec /bin/sh $0 "$@"


                                  Example:



                                  ~ (137) $ sh test.sh $(cat file.dat)
                                  a b
                                  a c
                                  a d
                                  a e
                                  b c
                                  b d
                                  b e
                                  c d
                                  c e
                                  d e
                                  ~ (138) $





                                  share|improve this answer





















                                  • 1





                                    Command substitution strips trailing newlines, so you're better off with something like <file.dat xargs test.sh than test.sh $(cat file.dat)

                                    – iruvar
                                    Mar 17 at 20:33














                                  5












                                  5








                                  5







                                  Here's one in pure shell.



                                  test $# -gt 1 || exit
                                  a=$1
                                  shift
                                  for f in "$@"
                                  do
                                  echo $a $f
                                  done
                                  exec /bin/sh $0 "$@"


                                  Example:



                                  ~ (137) $ sh test.sh $(cat file.dat)
                                  a b
                                  a c
                                  a d
                                  a e
                                  b c
                                  b d
                                  b e
                                  c d
                                  c e
                                  d e
                                  ~ (138) $





                                  share|improve this answer















                                  Here's one in pure shell.



                                  test $# -gt 1 || exit
                                  a=$1
                                  shift
                                  for f in "$@"
                                  do
                                  echo $a $f
                                  done
                                  exec /bin/sh $0 "$@"


                                  Example:



                                  ~ (137) $ sh test.sh $(cat file.dat)
                                  a b
                                  a c
                                  a d
                                  a e
                                  b c
                                  b d
                                  b e
                                  c d
                                  c e
                                  d e
                                  ~ (138) $






                                  share|improve this answer














                                  share|improve this answer



                                  share|improve this answer








                                  edited Mar 18 at 3:59

























                                  answered Mar 17 at 18:05









                                  EdCEdC

                                  512




                                  512








                                  • 1





                                    Command substitution strips trailing newlines, so you're better off with something like <file.dat xargs test.sh than test.sh $(cat file.dat)

                                    – iruvar
                                    Mar 17 at 20:33














                                  • 1





                                    Command substitution strips trailing newlines, so you're better off with something like <file.dat xargs test.sh than test.sh $(cat file.dat)

                                    – iruvar
                                    Mar 17 at 20:33








                                  1




                                  1





                                  Command substitution strips trailing newlines, so you're better off with something like <file.dat xargs test.sh than test.sh $(cat file.dat)

                                  – iruvar
                                  Mar 17 at 20:33





                                  Command substitution strips trailing newlines, so you're better off with something like <file.dat xargs test.sh than test.sh $(cat file.dat)

                                  – iruvar
                                  Mar 17 at 20:33











                                  1














                                  Using Perl we can do it as shown:



                                  $ perl -lne '
                                  push @A, $_}{
                                  while ( @A ) {
                                  my $e = shift @A;
                                  print "$e $_" for @A;
                                  }
                                  ' input.txt





                                  share|improve this answer




























                                    1














                                    Using Perl we can do it as shown:



                                    $ perl -lne '
                                    push @A, $_}{
                                    while ( @A ) {
                                    my $e = shift @A;
                                    print "$e $_" for @A;
                                    }
                                    ' input.txt





                                    share|improve this answer


























                                      1












                                      1








                                      1







                                      Using Perl we can do it as shown:



                                      $ perl -lne '
                                      push @A, $_}{
                                      while ( @A ) {
                                      my $e = shift @A;
                                      print "$e $_" for @A;
                                      }
                                      ' input.txt





                                      share|improve this answer













                                      Using Perl we can do it as shown:



                                      $ perl -lne '
                                      push @A, $_}{
                                      while ( @A ) {
                                      my $e = shift @A;
                                      print "$e $_" for @A;
                                      }
                                      ' input.txt






                                      share|improve this answer












                                      share|improve this answer



                                      share|improve this answer










                                      answered Mar 18 at 1:28









                                      Rakesh SharmaRakesh Sharma

                                      352115




                                      352115






























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