linux下好像命令-可以不写，譬如tar jxvf ...也可以tar -jxvf ？

Question

linux下好像命令-可以不写，譬如tar jxvf ...也可以tar -jxvf ？

Answer 1

You can’t say that. In fact, the example you used is rather special.
Among the options of the tar command - it can be written or not. If not used - the effect will be the same. However, it is still recommended to use -, after all, there are many specifications.

Let me show you an example where - cannot be ignored
[ioitboy@linux ~]$ ls -ld /
dr-xr-xr-x. 17 root root 4096 Jul 25 12:29 /
[ioitboy@linux ~]$ ls ld /
ls: cannot access ld: No such file or directory
/:
bin boot dev etc home lib lib64 media mnt opt ​​proc root run sbin srv sys tmp usr var

//The first command using - was executed successfully, but we found that the execution result of the second command was completely different and there was an error.
1, because - is not written, bash interprets ld as a file or directory and gives an error.
2, because - was not written, so bash did not get the request to use the -ld option. The output of ls / is given directly without listing the / directory information.

Finally, it is recommended to read more about man and --help. Learning the standardized command writing method can avoid some unexpected execution results.

Answer 2

The bad thing is the writing method of bsd, such as ps aux, you can write it like this because ps is ported from bsd

Answer 3

I don’t know much about the origin of the ps command, but you can take a look at the command line option parsing principle.
Those with - are UNIX style, those without are BSD style, and there are also GNU styles, etc. wait. .
You can simply understand the getopt and getopt_long functions. These two functions support UNIX style

Answer 4

I think this is a special case. Try other commands.

Answer 5

It can only be said that some can be omitted, such as the tar command, but some cannot be omitted. This mainly depends on the style of the command.