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[PATCH] filter ls output by filetype

From: Hal Ashburner
Subject: [PATCH] filter ls output by filetype
Date: Fri, 29 Nov 2013 00:49:19 +1100

ls filters by filename - leading dot -a -A or --ignore pattern
I have shell script that just shows directories by interposing `test` between two calls to ls in a pipeline to give me ls like behavior. Ls actually knows the filetype so I thought why not just filter on it in ls given filtering is something ls does? I noted this was not a rejected feature request and thought it might go well as a request accompanied by a patch.

was the best switch I could think of to achieve this end. I could easily be convinced there exists a better one. (--show-only? --showing?)

just list the block device files

./ls --just b /dev
loop0  loop3  loop6  ram1   ram12  ram15  ram4    ram7  sda   sda3  sda6    sda9
loop1  loop4  loop7  ram10  ram13  ram2   ram5    ram8  sda1  sda4  sda7    sdb
loop2  loop5  ram0   ram11  ram14  ram3   ram6    ram9  sda2  sda5  sda8

./ls --just=normal
ABOUT-NLS    config.log     NEWS
aclocal.m4    config.status  README
AUTHORS        configure      README-hacking
bootstrap   README-package-renamed-to-coreutils
bootstrap.conf    COPYING        README-prereq  README-release
ChangeLog    HACKING        README-valgrind
ChangeLog-2005    init.cfg       thanks-gen
ChangeLog-2006    Makefile
ChangeLog-2008    TODO

can filter on two types by applying the switch twice.

./src/ls --just=normal --just=symbolic-links -l test
total 0
lrwxrwxrwx 1 hal hal 13 Nov 29 00:20 link-to-somefile -> test/somefile
-rw-rw-r-- 1 hal hal  0 Nov 29 00:20 somefile

Why might rejection of this feature and patch be a good idea?
You can get this kind of thing done (sort of) with
$ find . -type d --maxdepth=1 -ls
or shell globbing abuse eg
$ ls -d */
but obviously such things are not ls and lose the familiar and consistent ls options such as find displaying a differing long format, no colored output, sorting, control of display of dotfiles etc. However all of these alternatives' shortcomings can be alleviated with fairly ordinary shell pipelines involving sed and/or test at the cost of a simple, robust and convenient user interface as provided by ls.

Shortcomings/BUGS/Possible future enhancements :
1) doesn't work with -R for anything except directories
2) Doesn't have a mode to filter based on permissions (eg show only executables or setuid etc).
3) Doesn't follow symbolic links and then filter them based on the type of file they are pointing at and I haven't yet worked out how to add the command interface for "including symlinks to" in a way that is not too ugly.
4) Others that exist of which I haven't considered.

On the off chance that there does happen to be interest in this feature and patch by coreutils hackers, I am more than happy to assign the copyright to GNU on the understanding it will be published under the appropriate version of the GPL for coreutils.
The patch should apply cleanly to the current default git checkout. I'm subscribed to the list and interested in any and all feedback.

Thank you for taking the time to give this request an appropriate level of consideration.

Kind regards,
Hal Ashburner

Attachment: ls.patch
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