A shell is terminology for a command-line interpreter most commonly used with Unix-like operating systems, but also used to interact with GUI-based operating systems in a more granular fashion. Not only does it allows the user to run programs from a text interface, but frequently offers basic ...
74
votes
3answers
20k views
What is the difference between double and single square brackets in bash?
I just wondered what exactly the difference between
[[ $STRING != foo ]]
and
[ $STRING != foo ]
is, apart from that the latter is posix-compliant, found in sh and the former is an extension ...
51
votes
10answers
14k views
Unique Features of bash compared to zsh
I have been a zsh user for quite some time (before that tcsh and before that csh). I am quite happy with it, but was wondering if there are any compelling features of bash that do not exist in zsh. ...
32
votes
9answers
29k views
Shell command to monitor changes in a file - What's it called again?
I know there was a command on Unix that I could use to monitor a file and see changes that are getting written to it. This was quite useful especially for checking log files.
Do you know what it is ...
29
votes
1answer
4k views
What is the difference between a 'Login' and an 'Interactive' bash shell
What is the difference between a ‘Login’ and an ‘Interactive’ bash shell?
I have quoted Wikipedia below but can anybody give a better answer?
EDIT: This is a community wiki so maybe rather than ...
23
votes
5answers
2k views
Linux server out of space
I have been asked this question in two consecutive interviews, but after some research and checking with various systems administrators I haven't received a good answer. I am wondering if somebody can ...
22
votes
2answers
5k views
Colors in bash after piping through less?
When I have dircolors defined life is full of... color.
When I pipe ls through less to scroll around I lose the colors.
Any suggestions?
Thanks,
-Mathew
17
votes
3answers
789 views
What's the difference betwen the single dash and double dash flags on shell commands?
I'm new to working in the shell and the usage of these commands seems arbitrary. Is there a reason one flag has a single dash and another might have a double dash?
16
votes
2answers
1k views
nologin in /etc/shells is dangerous.. WHY?
I found this on the internet, while putting up a FTP server in FreeBSD.
Putting nologin into /etc/shells potentially creates a back door by
which those accounts can be used with FTP.
(see: ...
15
votes
8answers
4k views
Is there any reason to use bash over zsh?
I'm curious about why one would want to run bash instead of zsh. I mean zsh is fully backwards-compatible with bash. Don't get me wrong: I don't dislike bash or anything. I just genuinely want to ...
15
votes
2answers
2k views
What is /usr/bin/[?
I was just poking around in /usr/bin and I found an ELF binary file called [. /usr/bin/[. I have never heard of this file and my first thought was that it was a clever way of hiding a program, ...
14
votes
6answers
7k views
How do I join two named pipes into single input stream in linux
Using pipes | feature in linux I can forward chain the standard input to one or several output streams.
I can use tee to split the output to seperate sub processes.
Is there a command to join two ...
14
votes
6answers
8k views
What does 'set -e' do, and why might it be considered dangerous?
This question has appeared on a pre-interview quiz and it's making me crazy. Can anyone answer this and put me at ease? The quiz has no reference to a particular shell but the job description is for a ...
14
votes
4answers
38k views
Adding a directory to $PATH in CentOS?
We just got our new server(s) up and we're running CentOS on them all. After successfully installing Ruby Enterprise Edition, I would now like to add the REE /bin (located at ...
14
votes
2answers
4k views
How can I check in bash if a shell is running in interactive mode?
How can I tell (in ~/.bashrc) if I'm running in interactive mode, or, say, executing a command over ssh. I want to avoid printing of ANSI escape sequences in .bashrc if it's the latter.
13
votes
21answers
17k views
Finding the Public IP address in a shell script
I can find my IP address using ifconfig or hostname -i command.
But how do I find my Public IP?
(I have a static public IP but I want to find it out using unix command)
13
votes
5answers
16k views
How to hide the output of a shell application in Linux?
How to hide the screen output (printf) of a shell application in Linux?
13
votes
12answers
8k views
How to pass alias through sudo
I have an alias that passes in some parameters to a tool that I use often. Sometimes I run as myself, sometimes under sudo. Unfortunately, of course, sudo doesn't recognise the alias.
Does anyone ...
13
votes
5answers
19k views
How can I kill all stopped jobs?
When I try to exit from my Linux server I get the message:
There are stopped jobs.
: Is there a single command to kill these?
13
votes
7answers
7k views
Live view of Linux shell commands executed by another user?
Is it possible for the root user in Linux to have a real-time (or close to real-time) view of the shell commands being run by another user logged in via a terminal or SSH? Obviously they're stored in ...
13
votes
3answers
6k views
12
votes
4answers
2k views
What is /bin/dash?
I thought /bin/sh was a symlink to my shell of choice. I've always used bash, so I assumed that /bin/sh would point to /bin/bash. It turns out, though, that it points to /bin/dash.
It gets funnier. I ...
12
votes
5answers
3k views
Adding a timestamp to bash script log
I have a constantly running script that I output to a log file:
script.sh >> /var/log/logfile
I'd like to add a timestamp before each line that is appended to the log. Like:
Sat Sep 10 21:33:06 ...
11
votes
2answers
7k views
Where's my tab completion and up-arrow behavior? (Ubuntu 10.04)
I'm new to Linux, trying Ubuntu 10.04, preconfigured by host.
When I log in (SSH) using the preconfigured account, the shell prompt is: user@hostname:~$
The up arrow scrolls through the list of ...
10
votes
7answers
6k views
How to log every linux command to a logserver
I want every single command typed to go to a logserver. Already configured is the syslog-ng to send all logs to the logserver.
I'm interested in any and all methods to do this. I would expect ...
10
votes
6answers
20k views
Run a shell script as a different user
What's a good way of running a shell script as a different user. I'm using Debian etch, and I know which user I want to impersonate.
If I was doing it manually, I would do:
su postgres
...
10
votes
4answers
937 views
How to remove many (200 000) files?
I must remove 200 000 files (all of them) from a folder, and I don't want to delete the folder itself.
using rm, I get an "Argument list too long" error.
I've tried to do something with xargs, but ...
10
votes
7answers
496 views
Why is this file hidden when you run ls?
EDIT: I totally forgot about this thread. It turns out I had a bad hard disk. We had to redeploy this server for other needs so I finally got around to replacing the one bad disk and we're back in ...
10
votes
2answers
217 views
backslash at the beginning of a command
In Installing RVM manual I see a lot of lines starting with '\':
Install RVM with ruby:
$ \curl -L https://get.rvm.io | bash -s stable --ruby
I'd think it is just mistype but they repeat ...
10
votes
9answers
729 views
Is there a paging version of `watch`?
Under a UNIX shell, how can I get a similar effect to the watch command, but with paging so that I can scroll around in the output if it takes up more than one screen?
In other words, I want a ...
10
votes
3answers
219 views
piping a password and security
I sometimes do echo "secret" | mysql -u root -p .... Now I'm concerend about security here: can someone listing all processes see the password?
To check I tried with echo "test" | sleep 1000 and the ...
10
votes
4answers
488 views
Is BitTorrent good for copy files between servers in the workplace?
I have 1 source server that contains about 30GB of files that I want to copy to 7 other servers. I currently SCP the files over to the first four servers and when that transfer is complete SCP to the ...
9
votes
6answers
2k views
what are Powershell's advantages over cygwin/unix-shell
The obvious difference I'm aware of, is the ability to interface to certain MS products, such as Exchange. But for one not having to administer such products, what are the advantages of Powershell? ...
9
votes
5answers
274 views
How do I change to the directory I just moved that file to?
So lets assume I've just done:
mv ./myfile /to/some/other/place/
And I now decide I want to follow the file, and go into that directory.
Whilst I could head for the mouse, select the text, type ...
9
votes
2answers
6k views
Proxy exceptions when using $http_proxy env var?
In a typical browser, when we set a proxy server, we can define a list of hostnames/IP addresses that are not to use the proxy server. How do we accomplish the same thing when using $http_proxy? I ...
9
votes
6answers
3k views
What distributed shell utilities do people feel are good, flexible, and easy to use? [closed]
I've been searching and collecting links for a lot of them, but many of these tools don't have enough use case or demonstration documentation to be able to evaluate their potential worth without ...
9
votes
3answers
158 views
Find's -true option: what for?
GNU find (and others?) has a -true test along with the normal -name, -mode, -user and so on. From the man page:
-true Always true.
Every time I see the man page I notice this and wonder when ...
8
votes
8answers
1k views
Comparison of Unix shells
Of the major Unix shells (bash, ksh, tcsh, zsh, others?), are there any compelling reasons to use one over another?
Which is the most interactive/command-line friendly?
Which is the most ...
8
votes
8answers
3k views
How to determine if I'm logged in via SSH?
I'm currently setting up a fairly complex bash configuration which shall be used on multiple machines. I try to find out if it is possible to determine whether I'm logged in via SSH or on a local ...
8
votes
2answers
936 views
How can I set environment variable for just one command in fish shell?
In bash, I can do EDITOR=vim crontab -e. Can I get similar effect in Fish shell?
8
votes
1answer
4k views
How to interpret output from Linux 'top' command?
Following a discussion made HERE about how PHP-FPM consuming memory, I just found a problem in reading the memory in top command. Here is a screenshot of my top just after restarting PHP-FPM. ...
8
votes
7answers
4k views
BASH shell session logging on remote host
What's the best method of logging a BASH shell session to a file on the host machine?
The preferred output format would be equivalent to PuTTY's "printable output" log setting, as viewed by the user ...
7
votes
5answers
6k views
Shell command to see the HTTP headers
Is there a shell command to see the headers of a HTTP request?
For example, I would like to know what the headers retrieved from www.example.com/test.php are
How can I do this?
7
votes
6answers
4k views
Find out how many DNS Queries/month via WHM or SSH?
Is it possible? We have complete control over our DNS server and the server actually being pointed to. We are interested in how many DNS Queries we are currently getting, as we want to move to Ultra ...
7
votes
6answers
8k views
Linux: using find to locate files older than <date>
find has good support for finding files the more modified less than X days ago, but how can I use find to locate all files modified after a certain date?
I can't find anything in the find man page to ...
7
votes
4answers
2k views
How do I setup SFTP for sites without giving shell access?
I'd like to use SFTP for all the sites on my cPanel CentOS server as we had an FTP password hacked before (not hard). However I don't want each sites SFTP account to have shell access (not even jailed ...
7
votes
2answers
6k views
When to use single-quote, double-quote in grep?
While trying to search for a simple pattern "hello" in a file, all the following forms of grep work:
grep hello file1
grep 'hello' file1
grep "hello" file1
Is there a specific case where one of ...
7
votes
3answers
11k views
How to list symbolic link chains?
Given this example:
mkdir a
ln -s a b
ln -s b c
ln -s c d
If I execute:
ls -l d
It will show:
d -> c
Is there a way for ls or any other linux command to show d -> c -> b -> a ...
7
votes
2answers
2k views
What is the best way to set an environmet variable in .bashrc?
When setting up a variable in .bashrc should I use
export VAR=value
or would
VAR=value
be enough?
What is exactly the difference (if there is one)?
7
votes
1answer
2k views
How to close GUI and go into pure shell mode in RedHat enterprise Linux 6?
I'm new to linux. How to close GUI and go into pure shell mode in RedHat enterprise Linux 6? I don't want the GUI. I just want to learn some shell scripts.
Thanks.
7
votes
3answers
4k views
Force SSH to use a specific shell
Is there any way to force SSH to use a particular shell on the remote end, regardless of what the user's default shell is?
I've tried solutions akin to:
ssh host.domain.com /bin/bash -c ...
