Sort everything except the header

Question

Sometimes I want to sort stuff, but not the header. So, for example, when I list loaded modules in Apache, there is a 1-line header that gets included in the sort:

 $ /usr/local/apache2/bin/apachectl -M | sort

 alias_module (shared)
 asis_module (static)
 cache_disk_module (static)
 cache_module (static)
 core_module (static)
 data_module (static)
 env_module (shared)
 ext_filter_module (static)
 file_cache_module (static)
 filter_module (shared)
 headers_module (shared)
 heartbeat_module (static)
 heartmonitor_module (static)
 http_module (static)
 include_module (static)
 info_module (static)
Loaded Modules:
 log_config_module (shared)
 macro_module (static)
 mime_module (shared)
 mpm_event_module (static)
 ratelimit_module (static)
 reqtimeout_module (shared)
 setenvif_module (shared)
 so_module (static)
 ssl_module (static)
 status_module (shared)
 substitute_module (static)
 unixd_module (static)
 version_module (shared)
 watchdog_module (static)

I tried using the -b option, but that had no effect. In any case, ignoring leading spaces would just be a workaround anyway. What I really want to do is exclude N lines of header from the sort. How can I do that?

score 0 · Answer 1 · answered Jan 11 '18 at 15:19

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I figured out that this can be done just by using a numeric argument to head. Since the rest of the lines, except the head still get delivered to stdout, sort can receive the rest of the lines:

$ /usr/local/apache2/bin/apachectl -M | { head -1; sort; }

Put however many lines of header there are after head (here it is 1).

answered Jan 11 '18 at 15:19

Tyler Durden

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with most `head` implementations (ksh93's `head` builtin being an exception), that won't work properly as `head` will read its input by block so typically read more than one line of the input. Try `seq 10 | { head -1; sort; }` for instance. – Stéphane Chazelas Jan 11 '18 at 15:58
@StéphaneChazelas It works fine on my generic Debian system. I can't get the seq thing to work, can you give a full example using my statement? – Tyler Durden Jan 11 '18 at 16:07
That will depend on how fast `apachectl` outputs the second and following lines. If it outputs them at the same time as the header (within the same `write()` system call) or before `head` has read the first line, then they will be eaten by `head`. `line`, or `IFS= read -r line` or ksh93's `head` builtin avoid the problem by reading the input one byte at a time and stop reading as soon as they see the delimiter of the first line. – Stéphane Chazelas Jan 11 '18 at 17:27

score 0 · Answer 2 · edited Jan 11 '18 at 17:50

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You can also use tail -n+3 to start on the third line, assuming the blank line was the second line of the output.

$ /usr/local/apache2/bin/apachectl -M | tail -n+3 | sort

edited Jan 11 '18 at 17:50

Kevin Lemaire

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answered Jan 11 '18 at 15:23

NomadMaker

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The problem with this solution is that it doesn't print the header. – Tyler Durden Jan 11 '18 at 16:09
You are right. However, the following seems to work and I will edit my answer if allowed. – NomadMaker Jan 12 '18 at 01:01
I was wrong. I was trying to duplicate contents of /dev/stdin as it came out of apachectl and send it to both head and tail, and then recombine them to be piped to sort. I hate to say it, but I can't make head or tails of this. :) – NomadMaker Jan 12 '18 at 01:22

score 0 · Answer 3 · answered Jan 11 '18 at 16:14

sed -n '1p' filename;sed -r "s/\s+//g" l.txt| sed '/^$/d' | sed -n '1!p'  | sort -n

sed -n '1p' filename ==>command will first display the Header line.

sed -r "s/\s+//g" l.txt| sed '/^$/d' | sed -n '1!p' | sort -n ==>it will print from 2nd line to end of file and sort it.

If you want to get it sorted from different line . You can just change the line number in command.

Let me know for any doubts.

Sort everything except the header

3 Answers3