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

Question

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 updator_error_log.txt

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

.  
..  
.bash_history  
.ssh  
updator_error_log.txt

Answer 1

Yes:

ls -a | cat

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

Answer 2

Use man ls to see if your ls supports the -1 option (that the "one" digit, not a lowercase letter "L" - thanks @slashmais), e.g.

http://docs.sun.com/app/docs/doc/819-2239/ls-1

...

-1

   Prints one entry per line of output.

GNU/Linux's ls does support it, so use:

ls -1a

Answer 3

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.

---

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.