How do I list one filename per output line in Linux?

I'm using ls -a command to get the file names in a directory, but the output is in a single line.

Like this:

.  ..  .bash_history  .ssh  updater_error_log.txt

I need a built-in alternative to get filenames, each on a new line, like this:

.  
..  
.bash_history  
.ssh  
updater_error_log.txt

Use the -1 option (note this is a "one" digit, not a lowercase letter "L"), like this:

ls -1a

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First, though, make sure your ls supports -1. GNU coreutils (installed on standard Linux systems) and Solaris do; but if in doubt, use man ls or ls --help or check the documentation. E.g.:

$ man ls
...
       -1     list one file per line.  Avoid '\n' with -q or -b

Yes, you can easily make ls output one filename per line:

ls -a | cat

Explanation: The command ls senses if the output is to a terminal or to a file or pipe and adjusts accordingly.

So, if you pipe ls -a to python it should work without any special measures.

Ls is designed for human consumption, and you should not parse its output.

In shell scripts, there are a few cases where parsing the output of ls does work is the simplest way of achieving the desired effect. Since ls might mangle non-ASCII and control characters in file names, these cases are a subset of those that do not require obtaining a file name from ls.

In python, there is absolutely no reason to invoke ls. Python has all of ls's functionality built-in. Use os.listdir to list the contents of a directory and os.stat or os to obtain file metadata. Other functions in the os modules are likely to be relevant to your problem as well.

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If you're accessing remote files over ssh, a reasonably robust way of listing file names is through sftp:

echo ls -1 | sftp remote-site:dir

This prints one file name per line, and unlike the ls utility, sftp does not mangle nonprintable characters. You will still not be able to reliably list directories where a file name contains a newline, but that's rarely done (remember this as a potential security issue, not a usability issue).

In python (beware that shell metacharacters must be escapes in remote_dir):

command_line = "echo ls -1 | sftp " + remote_site + ":" + remote_dir
remote_files = os.popen(command_line).read().split("\n")

For more complex interactions, look up sftp's batch mode in the documentation.

On some systems (Linux, Mac OS X, perhaps some other unices, but definitely not Windows), a different approach is to mount a remote filesystem through ssh with sshfs, and then work locally.

you can use ls -1

ls -l will also do the work

You can also use ls -w1

This allows to set number of columns. From manpage of ls:

   -w, --width=COLS
          set output width to COLS.  0 means no limit

ls | tr "" "\n"

Easy, as long as your filenames don't include newlines:

find . -maxdepth 1

If you're piping this into another command, you should probably prefer to separate your filenames by null bytes, rather than newlines, since null bytes cannot occur in a filename (but newlines may):

find . -maxdepth 1 -print0

Printing that on a terminal will probably display as one line, because null bytes are not normally printed. Some programs may need a specific option to handle null-delimited input, such as sort's -z. Your own script similarly would need to account for this.