The shell is unix's command-line interface. You can type commands in a shell interactively, or write scripts to automate tasks.
283
votes
4answers
47k views
What is the exact difference between a 'terminal', a 'shell', a 'tty' and a 'console'?
I think these terms almost refer to the same thing, when used loosely:
terminal
shell
tty
console
What exactly does each of these terms refer to?
30
votes
4answers
2k views
Redirecting stdout to a file you don't have write permission on
When you attempt to modify a file without having write permissions on it, you get an error:
> touch /tmp/foo && sudo chown root /tmp/foo
> echo test > /tmp/foo
zsh: permission ...
25
votes
4answers
8k views
Why is `while IFS= read` used so often, instead of `IFS=; while read..`?
It seems that normal practice would put the setting of IFS outside the while loop in order to not repeat setting it for each iteration... Is this just a habitual "monkey see, monkey do" style, as it ...
27
votes
2answers
2k views
$VAR vs ${VAR} and to quote or not to quote
I can write
VAR=$VAR1
VAR=${VAR1}
VAR="$VAR1"
VAR="${VAR1}"
the end result to me all seems about the same. Why should I write one or the other? are any of these not portable/POSIX?
35
votes
11answers
27k views
How can I get distribution name and version number in a simple shell script?
I'm working on a simple bash script that should be able to run on Ubuntu and CentOS distributions (support for Debian and Fedora/RHEL would be a plus) and I need to know the name and version of the ...
30
votes
7answers
4k views
How do I delete a file whose name begins with “-” (hyphen a.k.a. dash or minus)?
How do you remove a file whose filename begins with a dash (hyphen or minus) -? I'm ssh'd into a remote OSX server and I have this file in my directory:
tohru:~ $ ls -l
total 8
-rw-r--r-- 1 me ...
19
votes
3answers
4k views
How to pass parameters to an alias?
For bash script, I can use "$@" to access arguments. What's the equivalent when I use an alias?
42
votes
5answers
22k views
Allow setuid on shell scripts
The setuid permission bit tells Linux to run a program with the effective user id of the owner instead of the executor:
> cat setuid-test.c
#include <stdio.h>
#include <unistd.h>
int ...
18
votes
4answers
5k views
Difference between Login Shell and Non-Login Shell?
I understand the basic difference between an interactive shell and a non-interactive shell. But what exactly differentiates a login shell from a non-login shell?
Can you give examples for uses of a ...
27
votes
3answers
2k views
How to use `which` on an aliased command?
Like most users, I have a bunch of aliases set up to give a default set of flags for frequently used programs. For instance,
alias vim='vim -X'
alias grep='grep -E'
alias ls='ls -G'
The problem is ...
37
votes
2answers
9k views
What does “--” (double-dash) mean?
I have seen -- used in the compgen command.
For example:
compgen -W "foo bar baz" -- b
What is the meaning of the --.
117
votes
4answers
6k views
What's the difference between $(stuff) and `stuff`?
Running top -p $(pidof init) and top -p `pidof init` gives the same output. Are these two ways of doing the same thing, or are there differences?
19
votes
7answers
6k views
Batch renaming files
I have a directory full of images:
image0001.png
image0002.png
image0003.png
...
And I would like a one-liner to rename them to (say).
0001.png
0002.png
0003.png
...
How do I do this?
25
votes
5answers
7k views
How to test what shell I am using in a terminal?
How to check what shell I am using in a terminal? What is the shell I am using in MacOS?
30
votes
11answers
9k views
Get exit status of process that's piped to another
I have two processes foo and bar, connected with a pipe:
$ foo | bar
bar always exits 0; I'm interested in the exit code of foo. Is there any way to get at it?
