Question

I’ve been trying to find a way of sorting this with standard commandline tools, bash, awk, sort, whatever but can’t find a way apart from using perl or similar.

Any hint?

Input data

header1
3
2
5
1

header2
5
1
3
.....
.....

Output data

header1
1
2
3
5

header2
1
....

Thanks

Answer 1

Assumes sections are separated by blank lines and the header doesn’t necessarily contain the string “header”. Leaves the sections in the original order so the sort is stable. Reads from stdin, displays on stdout.

#!/bin/bash

function read_section() {
    while read LINE && [ "$LINE" ]; do echo "$LINE"; done
}

function sort_section() {
    read HEADER && (echo "$HEADER"; sort; echo)
}

while read_section | sort_section; do :; done

Or as a one-liner:

cat test.txt | while (while read LINE && [ "$LINE" ]; do echo "$LINE"; done) | (read HEADER && (echo "$HEADER"; sort; echo)); do :; done