Finding intersection of two lists in shell

I got thrown up with some more tasks to perform on shell.

First was to extract numbers from long list of text. For ex, you have text as :

[
	NumberLong(90),
	NumberLong(123),
	NumberLong(218),
	NumberLong(221),
	NumberLong(294),
	NumberLong(317),
	NumberLong(319),
	NumberLong(322),
	NumberLong(328),
	NumberLong(344),
	NumberLong(348)
]

To simple extract numbers from this file, we’ll use pcregrep command to capture the regex group and output it.

#!/bin/bash
cat input.txt | pcregrep -o1 -i '([0-9]+)' > output.txt

Second was to compare such two lists and result the numbers which are present in first file but not in second and vice-versa

This is where comm kicks in. It keeps as input two lexically sorted inputs and output the result such as :

The comm utility reads file1 and file2, which should be sorted lexically, and produces three text columns as output: lines only in file1; lines only in file2; and lines in both files.

#!/bin/bash
comm -23 <(sort first_file.txt ) <(sort second_file.txt) | sort -n

Note that comm command expects input to be lexically sorted and not numerically sorted, hence its necesary to sort the file even if its numerically sorted.