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When I added !! in the end of echo command, it gave some output but I am unable to understand the output of the command. What does !! actually do in Linux?
!! Refer to the previous command. This is a synonym for `!-1'
Assuming your example is something like this:
echo hello!!
The answer depends on what shell you are using. Assuming bash merely because this is what I usually use:
From bash man page:
!! Refer to the previous command. This is a synonym for `!-1'.
This means that the command above will print hello followed by the previous command line from shell command history.
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first up, a linux newbie.
I made a typo and I have no idea what I've walked into, and documentation to no avail.
Screen shot:
running
man tail
unfortunately provided no help either.
what is this command doing?
Exit by using ctrl + C
The apostrophe ( ' ) has nothing to do with tail command. What it really does is it allows you to insert multi line text in commands.
$ echo 'hello
> world'
hello
world
Don't forget to add an apostrophe at end to enclose the text.
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I have just started learning the Linux system and I need some help to translate the following to English:
grep WARNING readme.txt
and
grep WARNING readme.txt > warnings.txt
This is a homework question that i have researched myself but having trouble learning exactly what it means.
thanks in advance.
Try making a file on your computer named readme.txt. Put some lines of text in there, and make sure that some lines say "WARNING" while other lines do not.
Then run your first command and observe its output.
Then run your second command and observe its output and observe what was written to warnings.txt.
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I am following a book on Linux. One of the first commands is to execute who am i. It should return my username. However, it returns an empty prompt.
What am I missing?
I am using Fedora 25.
When you write:
who am i
You're actually passing two parameters ("am" and "i") to the who command:
:~$ who --help
Usage: who [OPTION]... [ FILE | ARG1 ARG2 ]
You want to do (without the spaces; it's a different function):
whoami
to get what you want.
When you execute the command from a terminal in Gnome, it does not return information. However, it does show results you if execute it in a tty terminal.
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To clarify, when entering the default shell in OS X it appears as:
pcname:~ username$
and changing directories appears as:
pcname:myFolder~ username$
however, in my experience with linux distros, the shell appears as:
username#pcname:~$
what is the purpose for the differences in syntax?
What I do is the following: On the system that has the promt the way I want it, I type:
echo $PS1
I copy the result, say, \u#\h \w\a \$ and then edit the ~/.bashrc on the system that I want to use with the line:
export PS1="\u#\h \w\a \$ "
And then I get the same prompt on that system as well.
If you want to get creative, have a look here
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I have used a command called 'cat /etc/group' what does this command mean and do.Can you tell me what each part of the command does please use simple terms.
You can find the answer to your question explained better than any of us ever could with this command:
man cat
It prints to standard output the contents of the file at the location /etc/group
Ok so cat outputs the file, which (in your case) contains basic info about groups.
If you are interested in what are the groups just click here