How do I sort a file after a certain row in bash?

Question

I am trying to sort a file and store the output into a tmp file. This is what my file looks like:

this_is_my_file (with no extension)

Names   Last_Name_Initial
---
Alex   G
Nick   D
Jon   J
Cain   V
Anderson   S
Chris   W

I know the command to sort the file is sort -n $PWD/this_is_my_file -o tmp but how to I start the sort after the ---? And a follow up question, how can you distinguish between a text or xml file if the file you are comparing has no extension?

You can sort by second column since it dont have `---` – Rahul Jun 17 '14 at 19:14 — Rahul, Jun 17 '14 at 19:14
@Rahul I want to sort the first column – Redson Jun 17 '14 at 19:16 — Redson, Jun 17 '14 at 19:16

anubhava · Accepted Answer · 2014-06-17T19:29:42.233

2

You can use:

head -n 2 file && tail -n +3 file | sort
Names   Last_Name_Initial
---
Alex   G
Anderson   S
Cain   V
Chris   W
Jon   J
Nick   D

It does the job as follows:

Uses head -n 2 to get first 2 header lines
Used tail -n +3 to get all lines starting from 3rd line
Pipes tail's output with sort
Merges head's output with tail+sort using &&

To redirect output you can use grouping in shell {...}

{ head -n 2 file && tail -n +3 file | sort; } > output

edited Jun 17 '14 at 19:29

answered Jun 17 '14 at 19:16

anubhava

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Explanation added in answer. – anubhava Jun 17 '14 at 19:21
how do you redirect the output into another file? `head -n 2 file && tail -n +3 file | sort > tmp`? – Redson Jun 17 '14 at 19:26

glenn jackman · Answer 2 · 2014-06-17T19:34:50.720

You could use a grouping construct:

{
    # read and print the first 2 lines
    read line; echo "$line"
    read line; echo "$line"
    # and sort the rest
    sort
} < this_is_my_file

Also, awk:

awk 'NR <= 2 {print; next} {print | "sort"}' this_is_my_file

a follow up answer: in general, on a unix-y system, the name file makes no guarantees about the contents of a file. However, you could see what the file command says about a file:

$ cat > contains_xml
<?xml version="1.0" encoding="ISO-8859-1" ?>
<foo>
<bar>baz</bar>
</foo>
$ file contains_xml
contains_xml: XML document text
$ cat > not_really.xml
this is plain text
$ file not_really.xml
not_really.xml: ASCII text

How do I sort a file after a certain row in bash?

2 Answers2