I have this bash script, which is generating every single combination of arrays in 5 digit long:

#!/usr/bin/env bash

for combo in \
do echo $combo;
done > output.txt

This will output:

$ ./script.sh

However, this is just freeze my computer. Is there any way to write the data into the file increasingly? Also, is it possible to separate the output to different files for example at every 65536 lines? like output1.txt, output2.txt, output3.txt?

Thank You for your help!

5 Answers 5


It's hard to generate those big permutation without holding up huge memory in shell.

You can try another language like Python:

$ python -c '
  import itertools, string
  l = [c for c in string.ascii_lowercase + string.digits]
  for p in itertools.product(l, l, l, l, l): print "".join(p)
' > file

You can use nested loops, though it will be slow:

for p in {a..z} {0..9}
do for q in {a..z} {0..9}
 do for r in {a..z} {0..9}
  do for s in {a..z} {0..9}
   do for t in {a..z} {0..9}
    do echo $p$q$r$s$t
done | split -l 65536 --numeric-suffixes=1 --additional-suffix=.txt - output

I found a nice tool called crunch which is written in C. You also have options to separate the output files by file size or lines!

Install: $ sudo apt-get install crunch

#!/usr/bin/env bash

crunch 5 5 abcdefghijklmnopqrstuvwxyz0123456789 -o output/START -c 1048576 # Excel line limit

This command in the output folder generates aaaaa-awrdd.txt, awrde-bi8gh.txt, bi8gi-b5pjl.txt, etc. files exactly with 1.048.576 lines, which is the Excel 2007+ line limit. It's also a super fast solution. generating of 60.000.000+ combinations in 58 files taken only 10s! Perfect!

  • cool! (+1) what is the meaning of " ... 5 5 ..." ?
    – JJoao
    Commented Nov 18, 2015 at 11:25
  • 1
    min-length and max-length of the output. of I use 4 5, than it will output aaaa and aaaaa variations too. But I like to separate into different files by length.
    – Lanti
    Commented Nov 18, 2015 at 11:39
  • One thing to make sure when you define the list of characters, use this format: The order MUST BE lower case characters, upper case characters, numbers, and then symbols. If you don't follow this order you will not get the results you want. You also have to escape special characters. More info $ man crunch
    – Lanti
    Commented Nov 18, 2015 at 11:45

For permutations, I use the following perl script to generate permutations:

use strict;
use Algorithm::Permute;

my $q=shift or die("usage permgen n word-set\n");

my $p = new Algorithm::Permute([@ARGV],$q);
while (my @res = $p->next) { 
  print @res,"\n"; }

This can be used to make permutations of very different sets. Example unicode dices:

permgen 2  ⚀ ⚁ ⚂ ⚃ ⚄ ⚅ | shuf -n 2

To generate your (HUGE) example we need to write: permgen 5 {a..z} {0..9}

In my old machine it takes 2s to generate 1_000_000 permutations

time permgen 5 {a..z} {1..9}| head -1000000| wc


bash will always allocate all elements in RAM before iterating over them with the for loop. You're effectively asking bash to allocate lots of RAM at once and your computer just doesn't have that much, that's why it crashes/freezes.

The combinations themselves don't require that much (my back of the envelope computations give around 500MB), but I suppose bash has a massive overhead when dealing with arrays.

I wonder how much free RAM you really have.

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .