unix interview questions
Top unix frequently asked interview questions
I set a passphrase when creating a new SSH key on my laptop. But, as I realise now, this is quite painful when you are trying to commit (Git and SVN) to a remote location over SSH many times in an hour.
One way I can think of is, delete my SSH keys and create new. Is there a way to remove the passphrase, while still keeping the same keys?
Source: (StackOverflow)
I wish to have long and short forms of command line options invoked using my shell script.
I know that getopts can be used, but like in Perl, I have not been able to do the same with shell.
Any ideas on how this can be done, so that i can use options like:
./shell.sh --copyfile abc.pl /tmp/
./shell.sh -c abc.pl /tmp/
In the above, both the commands mean the same thing to my shell, but using, getopts, I have not been able to implement these?
Source: (StackOverflow)
I am working on writing some scripts to Grep certain directories, but these directories contain all sorts of file types.
I want to grep just .h and .cpp for now, but maybe a few others in the future.
So far I have:
{ grep -r -i CP_Image ~/path1/;
grep -r -i CP_Image ~/path2/;
grep -r -i CP_Image ~/path3/;
grep -r -i CP_Image ~/path4/;
grep -r -i CP_Image ~/path5/;}
| mailx -s GREP email@domain.com
Can anyone show me how I would now add just specific file extensions?
Source: (StackOverflow)
I would like to run a find and replace on a html file through the command line.
my command looks something like this:
sed -e s/STRING_TO_REPLACE/STRING_TO_REPLACE_IT/g index.html > index.html
When I run this and look at the file afterward, it is empty. (it deleted the contents of my file)
when i run this after restoring the file again:
sed -e s/STRING_TO_REPLACE/STRING_TO_REPLACE_IT/g index.html
the stdout is the contents of the file, and the find and replace has been executed.
Why is this happening?
Source: (StackOverflow)
Is there a (unix) shell script to format JSON in human-readable form?
Basically, I want it to transform the following:
{ "foo": "lorem", "bar": "ipsum" }
... into something like this:
{
"foo": "lorem",
"bar": "ipsum"
}
Source: (StackOverflow)
I have a C++ application I'm in the process of optimizing. What tool can I use to pinpoint my slow code?
Source: (StackOverflow)
In PHP I would add strings together like this:
$foo = "Hello";
$foo .= " World";
So $foo would be "Hello World"
How would I do that in Bash?
Source: (StackOverflow)
In a Unix shell, if I want to combine stderr and stdout into the stdout stream for further manipulation, I can append the following on the end of my command:
2>&1
So, if I want to use "head" on the output from g++, I can do something like this:
g++ lots_of_errors 2>&1 | head
so I can see only the first few errors.
I always have trouble remembering this, and I constantly have to go look it up, and it is mainly because I don't fully understand the syntax of this particular trick. Can someone break this up and explain character by character what "2>&1" means?
Source: (StackOverflow)
$ time foo
real 0m0.003s
user 0m0.000s
sys 0m0.004s
Which of these three is meaningful when benchmarking my app?
Source: (StackOverflow)
How do I recursively grep all directories and subdirectories?
find . | xargs grep "texthere" *
Source: (StackOverflow)
I just installed node and npm through the package on nodejs.org and whenever I try to search or install something with npm it throws the following error, unless I sudo the command. I have a feeling this is a permissions issue? I am already the admin.
npm ERR! Error: EACCES, open '/Users/chietala/.npm/-/all/.cache.json'
npm ERR! { [Error: EACCES, open '/Users/chietala/.npm/-/all/.cache.json']
npm ERR! errno: 3,
npm ERR! code: 'EACCES',
npm ERR! path: '/Users/chietala/.npm/-/all/.cache.json' }
npm ERR!
npm ERR! Please try running this command again as root/Administrator.
npm ERR! System Darwin 12.2.0
npm ERR! command "node" "/usr/local/bin/npm" "search" "bower"
npm ERR! cwd /Users/chietala
npm ERR! node -v v0.10.4
npm ERR! npm -v 1.2.18
npm ERR! path /Users/chietala/.npm/-/all/.cache.json
npm ERR! code EACCES
npm ERR! errno 3
npm ERR! stack Error: EACCES, open '/Users/chietala/.npm/-/all/.cache.json'
npm ERR!
npm ERR! Additional logging details can be found in:
npm ERR! /Users/chietala/npm-debug.log
npm ERR! not ok code 0
Source: (StackOverflow)
How can I replace a newline (\n) using sed?
I unsuccesfully tried:
sed 's#\n# #g' file
sed 's#^$# #g' file
How to fix it?
Source: (StackOverflow)
Is there a command or an existing script that will let me view all of a *NIX system's scheduled cron jobs at once? I'd like it to include all of the user crontabs, as well as /etc/crontab, and whatever's in /etc/cron.d. It would also be nice to see the specific commands run by run-parts in /etc/crontab.
Ideally, I'd like the output in a nice column form and ordered in some meaningful way.
I could then merge these listings from multiple servers to view the overall "schedule of events."
I was about to write such a script myself, but if someone's already gone to the trouble...
Source: (StackOverflow)
There are a plethora of questions where people talk about common tricks, notably "Vim+ctags tips and tricks".
However, I don't refer to commonly used shortcuts that someone new to Vim would find cool. I am talking about a seasoned Unix user (be they a developer, administrator, both, etc.), who thinks they know something 99% of us never heard or dreamed about. Something that not only makes their work easier, but also is COOL and hackish. After all, Vim resides in the most dark-corner-rich OS in the world, thus it should have intricacies that only a few privileged know about and want to share with us.
Source: (StackOverflow)