Questions tagged [shell]
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 programming features such as variables, substitution, output redirection, and wildcards.
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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 found in ...
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14
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Shell command to monitor changes in a file
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 ...
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What is "-bash: !": event not found"
Try executing the following under a bash shell echo "Reboot your instance!"
On my installation:
root@domU-12-31-39-04-11-83:/usr/local/bin# bash --version
GNU bash, version 4.1.5(1)-release (i686-pc-...
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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 ...
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How to add 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:...
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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?
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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?
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What's the difference between 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?
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How to run command as user who has /usr/sbin/nologin as Shell?
All I need to do is to run a specific script as a particular user who does have the nologin/false shell indicated in /etc/passwd.
I would run the script as root and this should run as another user.
...
- 1,181
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How to let 'cp' command don't fire an error when source file does not exist?
I'm using Mac OS X.
I'm trying to copying some files with cp command for a build script like this.
cp ./src/*/*.h ./aaa
But this command fires an error if there is no .h file in ./src directory.
How ...
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Is there a way to do a remote "ls" much like "scp" does a remote copy?
Is there a way to do a remote "ls" much like "scp" does a remote copy in a standard linux shell?
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6
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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 /usr/lib/ruby-enterprise/...
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How do I join two named pipes into single input stream in linux
Using the 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 separate sub processes.
Is there a command to ...
Brad
76
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9
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Command to prepend string to each line?
Looking for something like this? Any ideas?
cmd | prepend "[ERRORS] "
[ERROR] line1 text
[ERROR] line2 text
[ERROR] line3 text
... etc
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6
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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.
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71
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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 before a certain date?
I can't find anything in the find man page to ...
- 7,056
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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?
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67
votes
10
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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. ...
- 1,899
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votes
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Choosing the shell that SSH uses?
How do I set the shell that is used when a user SSHs to a server. For example I can't stand BASH and need to use ZSH, how do I make it so ZSH is loaded along with my profile (.zsh_profile) when I ssh ...
- 1,487
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How to split a PEM file
Note : This is not really a question because I already found the answer but since I didn't find it easily here I will post it so that it can benefit others.
Question : How to read a concatenated PEM ...
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votes
5
answers
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How can I hide the output of a shell application in Linux?
How can I hide the screen output (printf) of a shell application in Linux?
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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 voting ...
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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
./backup_db....
- 1,042
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votes
3
answers
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find command default sorting order
what is the default sorting order for entries returned by the linux find command?
For example, if I issue
find . -type f -name '*mp3'
and the output consists of multiple files across multiple sub-...
- 583
57
votes
7
answers
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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 'complicated,...
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votes
6
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Cron: Only get errors in emails?
I finally set up a realistic backup schedule on my data through a shell script, which are handled by cron on tight intervals. Unfortunately, I keep getting empty emails each time the CRON has been ...
- 1,599
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1
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What's the difference between sudo su - postgres and sudo -u postgres?
PostgreSQL users peer authentication on unix sockets by default, where the unix user must be the same as the PostgreSQL user. So people frequently use su or sudo to become the postgres superuser.
I ...
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Templating with Linux in a Shell Script?
What I want to acomplish is:
Having a config file as template, with variables like $version $path (for example apache config)
Having a shell script that "fills in" the variables of the ...
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votes
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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 instead?...
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votes
23
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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)
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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?
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Faking the date for a specific shell session
I'm certainly trying to achieve something weird here, but I want to fake the date locally for a shell session on GNU/Linux.
I need to black-box test how a program behaves at different dates, and ...
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How to rename multiple files by replacing word in file name?
Replace ACDC to AC-DC
For example we have these files
ACDC - Rock N' Roll Ain't Noise Pollution.xxx
ACDC - Rocker.xxx
ACDC - Shoot To Thrill.xxx
I want them to become:
AC-DC - Rock N' Roll Ain't ...
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Run command as Linux "system" user (shell = /bin/false)
I created a "system" user in Ubuntu 11.04 (adduser --system) for running certain cron jobs, but sometimes I want to test things out by manually running commands as that user. What's the easiest way to ...
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votes
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answers
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Need to fix file permissions in a user's home directory
Does anyone have a tool or script that will recursively correct the file permissions on a directory?
On an Ubuntu Linux machine, a bunch of files were copied to a USB disk with full 777 permissions (...
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votes
1
answer
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Run command in detached tmux session
This is probably simple, but I really can't find out how you do it. I have read the man pages and googled without results.
Problem: How do I run a command in a detached tmux window?
Example: I want ...
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votes
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#!/bin/sh vs #!/bin/bash for maximum portability
I usually work with Ubuntu LTS servers which from what I understand symlink /bin/sh to /bin/dash. A lot of other distros though symlink /bin/sh to /bin/bash.
From that I understand that if a script ...
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Is there any reason to use bash over zsh? [closed]
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 ...
- 1,219
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votes
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Can't run AWS CLI from CRON (credentials)
Trying to run a simple AWS CLI backup script. It loops through lines in an include file, backs those paths up to S3, and dumps output to a log file. When I run this command directly, it runs without ...
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votes
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Append an echo to file?
In linux, how do I do something like
echo 'hello world' > log.txt
but instead of overwriting the contents of log.txt, it appends to the end of of log.txt?
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votes
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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 ...
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How do I exclude directories when listing files?
How do I exclude directories when listing files in the current directory?
ls .
^ will include directories in the listing.
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votes
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answers
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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 ...
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answers
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How can I display the IP address of an interface?
If I want to display the IP address that is assigned to eth1, how can I do this in Bash?
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Don't need the whole line, just the match from regular expression
I simply need to get the match from a regular expression:
$ cat myfile.txt | SOMETHING_HERE "/(\w).+/"
The output has to be only what was matched, inside the parenthesis.
Don't think I can use grep ...
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How to find the gateway IP address in Linux
What command can you use to find the Gateway IP Address (ie. home router address) for eth0 in Linux?
I need to get the IP address from a command line app to use in a shell script.
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Did a cat /dev/urandom - Broken terminal
Out of curiosity, when your shell character set breaks from doing something like cat /dev/urandom is there a way to fix that in place?
31
votes
6
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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 ...
Abhijeet Jahagirdar
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8
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Why does it take tens of seconds to get a shell prompt?
It's a sort of regular occurrence that, after SSHing to a server (or even opening a terminal on my Mac), the login banner prints immediately but it takes ~10 seconds to a minute for the shell prompt ...
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