Linux Command usage

Linux Command Usage Note-general Linux technology-Linux programming and kernel information. The following is a detailed description. Today, someone in the group asked how to view the user group name of the local machine. There is a group command, but only the user group name of the running user can be viewed.
You can use cat/etc/group to view the information, but there is a little more information in it. You can try to overwrite the rest of the information, think about grep, use a regular expression, and read it for a while, I did not write it out. I asked in the irc of # ubuntu-cn, and the answer will be available. Answers from brother
Cat/etc/group | cut-d ":"-f1

After finding out, cut is quite powerful and useful for extracting information:
Us @ us-laptop :~ $ Cut -- help
Usage: cut [Option]... [file]...
Print the specified part from each file to the standard output device.

Parameters required for long options are also required when short options are used.
-B, -- bytes = the list only selects the specified bytes.
-C, -- characters = the list only selects the specified characters
-D, -- delimiter = delimiter specified <分界符> Place tabs as the region demarcation
-F, -- fields = the list only selects the specified fields and prints all
Rows that do not contain delimiters, unless
-S option is specified
-N (ignore)
-- Complement complements the placeholder of the selected byte, character, or field
-S, -- only-delimited does not print rows without delimiters
-- Output-delimiter = Specify the string <字符串> As output delimiters
Input delimiters are used by default.
-- Help: displays the help information and leaves
-- Version: displays the version information and leaves.
The cut-d ":"-f1 above
-D is used to specify the delimiter. The default Delimiter is TAB, and then-fN is used to specify the input field. Here, f1 is used to output the first field, that is, the user group name. Here N can have multiple fields, separated by commas. or use range. for example, 1-3.

Then you can use this command to view all the user names on the machine.
Cat/etc/shadow | cut-d ":"-f1
This shadow file contains information of the local user. One thing is that this file must be accessed with the root permission.