Linux – Is it possible to change the default behavior of a command

Parsing the output of ls is always problematic. You should always use a different tool if you mean to process the output automatically.

In your particular case, your command was failing -- not because of some missing or incompatible argument to ls -- but because of the glob you were sending it. You were asking ls to list all results including hidden ones with -a, but then you were promptly asking it to only list things that matched the */ glob pattern which does not match things beginning with. and anything ls might have done was restricted to things that matched the glob. You could have used .*/ as a second glob to match hidden directories as well, or you could have left the glob off entirely and just let ls do the work. However, you don't even need ls for this if you have a glob to match.

One solution would be to skip the ls entirely and just use shell globing:*

$ du -s */ .*/ | sort -n

Another way which might be overkill for this example but is very powerful in more complex situations would be to use find:*

$ find ./ -type d -maxdepth 1 -exec du -s {} + | sort -n

Explanation:

• find ./ starts a find operation on the current directory. You could use another path if you like.
• -type d finds only things that are directories
• -maxdepth 1 tells it only to find directories in the current directory, not to recurse down to sub-directories.
• -exec [command] [arguments] {} + works much like xargs, but find gets to do all the heavy lifting when it comes to quoting and escaping names. The {} bit gets replaced with the results from the find.
• du -s you know

_{* Note that I used the -n operator for sort to get a numeric sorting which is more useful in than alphabetic in this case.}

Expanding on the comment by @SamiLaine for using man - one reason I didn't like it, was because I expected it to be tedious to set up, and I think this post will show that; but, it seems to work. First, some introduction can be found here:

• HowTo: Linux / UNIX Create a Manpage - nixCraft mentions sections, syntax, etc
• Creating Custom Man Pages | Linux Journal mentions txt2man (sudo apt-get install txt2man)
• 10.04 - How do I add a directory to MANPATH or INFOPATH? - Ask Ubuntu

First let's create the directory and add it to MANPATH:

mkdir ~/myreminderhelp
echo 'MANPATH=$MANPATH:'$(echo ~/myreminderhelp) >> ~/.bashrc

Let's test if it is found: close the terminal, open a new terminal; and then:

manpath -d 2>&1 | grep myrem

Unfortunately, this reports nothing for me; even if echo $MANPATH says :~/myreminderhelp.

Trying with global /etc/bash.bashrc (after deleting the line in local ~/.bashrc, and restarting terminal again):

sudo bash -c "echo 'MANPATH=$MANPATH:'$(echo ~/myreminderhelp)" # check home dir printout
sudo bash -c "echo 'MANPATH=$MANPATH:'$(echo ~/myreminderhelp) >> /etc/bash.bashrc"

Restart terminal; still manpath does not report this directory. Let's now try this:

sudo bash -c "echo 'MANDATORY_MANPATH  '$(echo ~/myreminderhelp) >> /etc/manpath.config"

Close and reopen terminal again; finally, we get:

$ manpath 
/usr/local/man:/usr/local/share/man:/usr/share/man:/media/extern/texlive/2011/bin/i386-linux/man:~/myreminderhelp

In fact, after finding this, I erased the line from /etc/bash.bashrc, and manpath still reports the directory. So, I guess editing /etc/manpath.config is all that is needed.

Ok, so let's create an example custom reminder file here:

echo "Just a bit of a reminder...

Use nmcli con --help" >> ~/myreminderhelp/nmcli-reminder.txt

Then use txt2man to get a man formatted file, and gzip it:

cat ~/myreminderhelp/nmcli-reminder.txt | txt2man > ~/myreminderhelp/nmcli-reminder.1
gzip ~/myreminderhelp/nmcli-reminder.1

Restart terminal again, try typing man nm and press TAB - autocompletion shows nmcli-reminder is not found...

So let's try put our files in a man section subfolder; the links above indicate section 7 would be appropriate; so:

mkdir ~/myreminderhelp/man7
mv ~/myreminderhelp/nmcli-reminder.* ~/myreminderhelp/man7/
tree ~/myreminderhelp # to check - ok

Restart terminal again; try typing man nm and press TAB - autocompletion finally works:

$ man nmcli # and here press TAB:
nmcli           nmcli-reminder

... but now we have this problem:

$ man nmcli-reminder 
No manual entry for nmcli-reminder

Damn it. Could be that currently, our file is nmcli-reminder.1.gz indicating section 1 - let's rename it:

mv ~/myreminderhelp/man7/nmcli-reminder.1.gz ~/myreminderhelp/man7/nmcli-reminder.7.gz
man nmcli-reminder

... and finally the man command works!

So for this use case, probably it's best to keep the source .txt files directly in ~/myreminderhelp/, and then generate man pages in the appropriate subfolder - as in:

$ tree ~/myreminderhelp/
~/myreminderhelp/
├── man7
│   └── nmcli-reminder.7.gz
└── nmcli-reminder.txt

... the appropriate generation commands for this being:

cat ~/myreminderhelp/nmcli-reminder.txt | txt2man > ~/myreminderhelp/man7/nmcli-reminder.7
gzip ~/myreminderhelp/man7/nmcli-reminder.7

And here is a ~/myreminderhelp/buildreminders.sh script:

#!/usr/bin/env bash

DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )"

for ix in $DIR/*.txt; do
  bx=$(basename $ix)
  isn=${bx%%.txt}
  echo Processing $isn;
  set -x
  # txt2man -t "$isn" -s 7 $ix > $DIR/man7/${isn}.7
  pandoc -f markdown -t man -s -o $DIR/man7/${isn}.7 $ix
  gzip --force $DIR/man7/${isn}.7
  { set +x; } 2>/dev/null
done

tree -a $DIR

EDIT: Turns out, it is very difficult to get txt2man to leave literal source code unformatted, as it tends to auto-extract information like man (sub)sections etc. I've modified the script above to use pandoc instead (via WritingManPages - HerzbubeWiki) -- at least with pandoc with a Markdown input, you have some control over what is literal preformatted text, and what isn't ...

However, both of these tools will indent contents, as is typical for a man page (since there, section headings are non-indented, rest of the text content as in paragraphs, is). And I'm not sure I end up liking that all too much...