mjhjmtu

In my current directory, I execute the command:
ls -1 and it gives a list of the current directory contents.

In the same directory, I repeat the command: ls and it gives me the same result, with perhaps a different formatted output.

Finally, I try to find out about the available commands by typing ls --help and the output is:

usage: ls [-ABCFGHLOPRSTUWabcdefghiklmnopqrstuwx1] [file ...]

It looks like the last option is 1 (#1). Can someone explain what the ls -1 does and how it's different to the standard ls command?

Yes, the formatting of the output is the only difference between ls -1 and ls without any options.

From the ls manual on my system:

 -1 (The numeric digit "one".) Force output to be one entry per line.
 This is the default when output is not to a terminal.

This is also a POSIX option to the ls utility.

The manual for ls on your system is bound to say something similar (see man ls).

Related:

• is piped ls the same as ls -1?

ls -1 lists one file per line. By default, when it’s outputting to a terminal, ls lists files in columns, whose number varies depending on the length of the file names and the available space on screen.

To find this kind of information, man ls works better than ls --help. (This is true for most commands.)

man ls contains (searched via /-1<Enter>)

 --format=WORD
 across -x, commas -m, horizontal -x, long -l, single-column -1, verbose -l, vertical -C

ls -1 triggers the single column mode. ls by default displays its content in multiple columns, just like the column command line tool would.