use crunch to generate all the possible IATA codes comsbination

Question

I don't really know how to formulate this, but I have a bunch of IATA codes, and I want to generate all the possible combinations ex : JFK/LAX, BOS/JFK, ...etc, separated by a character such as "/" or "|".

Answer 1

Here we assume your IATA codes are stored in the file file; one code per line.

crunch has the -q option which generates permutations of lines from a file. However, in this mode crunch ignores most of the other options like <max-len>, which would be important here to print only pairs of codes.

Therefore, it would be easier and faster to …

Use something different than crunch

For instance, try

join -j2 -t/ -o 1.1 2.1 file file | awk -F/ '$1!=$2'

If you really, really, really want, you can …

Translate the input into something crunch can work with

We translate each line from file to a unique single character, supply that list of characters to crunch, and then translate the result back.

crunch supports Unicode characters, so files with more than 255 lines are totally fine. Here we enumerate the lines in file by characters in Unicode's Supplementary Private Use Area-A. Therefore, file may have at most 65'534 lines.
If you need more lines, you could combine multiple Unicode planes, but at some point you might run into ARG_MAX issues. Also, with 65'534 lines you would already generate (a bit less than) 65'534^2 = 4'294'705'156 pairs, occupying more than 34 GB when translated into pairs of IATA codes.

I suspect the back-translation to be a huge slowdown, so above alternative seems to be better in every aspect (efficiency, brevity, maintainability, …).

# This assumes your locale is using any Unicode encoding,
# e.g. UTF-8, UTF-16, … (doesn't matter which one).

file=...
((offset=0xF0000))
charset=$(
  echo -en "$(bc <<< "obase=16;
    max=$offset+$(wc -l < "$file");
    for(i=$offset;i<max;i++) {\"\U\"; i}" |
    tr -d \\n
  )"
)
crunch 2 2 "$charset" -d 1@ --stdout |
iconv -t UTF-32 |
od -j4 -tu4 -An -w12 -v |
awk -v o="$offset" 'NR==FNR{a[o+NR-1]=$0;next} {print a[$1]"/"a[$2]}' "$file" -