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Editorial Team
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Asked: 2026-06-05T02:12:55+00:00

How can I revert the order of some blocks of text using only bash

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How can I revert the order of some blocks of text using only bash commands like sed and cat? What I want is something like tac, but instead of operating line by line, it would operate block by block. Example:

From

/Section 3/
Rabbits
Dogs
Cats

/Section 2/
Eagles
Mice

/Section 1/
Dogs
Rabbits
Lemmings

To

/Section 1/
Dogs
Rabbits
Lemmings

/Section 2/
Eagles
Mice

/Section 3/
Rabbits
Dogs
Cats

In some files, the beginning of the block is marked by a slash, as in the example above. In others, the blocks are marked only by the existence of one or more blank lines between them.

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1 Answer

  1. Editorial Team

    In emacs, you can use the sort-paragraphs command:

    Ctrl-xhMeta-xsort-paragraphsEnter

    In vim: https://superuser.com/questions/365094/sort-file-per-paragraph-in-vim

    Use the basic unix tools:

    awk -F'\n' -vRS='' -vOFS=',' '{$1=$1}1' input.txt |
    sort |
        tr ',' '\n' |
            sed 's@^/@\n/@'

    I use awk to transform the data to a csv, then sort the csv, at last I transform the csv back to list style.

    result:

    /Section 1/
Dogs
Rabbits
Lemmings

/Section 2/
Eagles
Mice

/Section 3/
Rabbits
Dogs
Cats

    Edit: Sorry, I didn’t look at your question very carefully. You can change the sort command to tac to reverse the order.

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