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ls

summary

    This subchapter looks at ls, a UNIX (and Linux) command.

    ls is the UNIX (and Linux) list command.

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ls

    This subchapter looks at ls, a UNIX (and Linux) command.

    ls is used to list files.

    The ls command was described in the first UNIX book, UNIX Programmer’s Manual, by Ken Thompson and Dennis Ritchie, published November 3, 1971.

list directory contents

    Use the ls command to list the contents of the current working directory.

    $ ls
    Desktop          Movies        Send registration
    Documents        Music         Sites
    Downloads        Pictures
    Library          Public
    $

PC-DOS equivalent

    ls -la is the UNIX equivalent of the MS-DOS or PC-DOS command DIR. You can add the PC-DOS equivalent to your shell session with the alias command. To make the change permanent, add the following line to the .bashrc file in your home directory. Note that if you add this PC-DOS/MS-DOS equivalent, only add the all upper case version, because the lower case type is an important UNIX command that you will also need.

    $ alias DIR="ls -la"

    ls -la | less is the UNIX equivalent of the MS-DOS or PC-DOS command DIR /P.

list all

    Type ls with the -A option to get a list of all entries other than . (single dot) and .. (double dot).

    $ ls -A

list with hints

    Type ls with the -F option to have special indicators for special files.

    $ ls -F
    Desktop/                Music/                  file01.txt
    Documents/              Pictures/               file02.txt
    Downloads/              Public/                 names
    Library/                Send registration@      numberfile.txt
    Movies/                 Sites/                  testdir/
    $

    A slash / will be added after every pathname that is a directory. An asterisk * will be added after every file that is executable (including scripts). An at sign @ will be displayed after each symbolic link. An equals sign = will be displayed after each socket. A percent sign % will be displayed after each whiteout. A vertical bar | will be displayed after each item than is a FIFO.

    ls -F is a builtin command in csh.

hidden files

    The -a option will give a list of all files, including hidden files.

    $ ls -a

gotchas

    Do not use the output of ls in a BASH for loop.

    $ for i in $(ls *.mp3); do # Wrong!
    $    command $i # Wrong!
    $ done # Wrong!
    
    $ for i in $(ls *.mp3) # Wrong!
    $ for i in `ls *.mp3` # Wrong!

    If any file name has spaces in it, then it will be word split. So, the MP3 for Alex Clair’s “Too Close” (number four song on his “The Lateness of the Hour” album) might be 04 Too Close. In that case, your command would run on the files “04”, “Too”, and “Close”, rather than “04 Too Close”. Additional errors likely to follow. Listen to the song “Too Close” for free.

    Double quote won’t work either because that will cause the entire output of the ls command to be treated as a single item. Your loop will run once on all of the file names conactenated together.

    $ for i in "$(ls *.mp3)"; # Wrong!

    The solution is to run your loop without even using ls, relying on BASH’s filename expansion. Don’t forget to check for the possibility that there are no qualifying files in the current directory.

    $ for i in *.mp3; do # Wrong!
    $    [[ -f "$i" ]] || continue
    $    command "$i"
    $ done

other

    On November 8, 2010, Ramesh Natarajan named this the number twelve (12) most frequently used UNIX/Linux command at this web page 50 Most Frequently Used UNIX / Linux Commands (With Examples).

    In June 2009, Ken Milberg named this command as one of the Top 50 universal UNIX commands at this web page Top 50 Universal INIX commands. Note that this web page requires agreeing to be spammed before you can read it.

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