On the Internet, including local networks, machines call each other by IP addresses. In order to access machine B from machine A using the name of machine B, machine A has to have some way to map the name of B to its IP address. There are three ways to declare machine names on A: a hosts file. ...

The Stack Overflow Regular Expressions FAQ If you want to truly learn regular expressions, then read Jeffrey Friedl's "Mastering Regular Expressions" from beginning to end (3rd edition, on Amazon) Quantifiers Zero-or-more: *:greedy, *?:reluctant, *+:possessive One-or-more: +:greedy, +?:r...

I wrote a regular expression which works well in a certain program (grep, sed, awk, perl, python, ruby, ksh, bash, zsh, find, emacs, vi, vim, gedit, …). But when I use it in a different program (or on a different unix variant), it stops matching. Why?

When you want to run multiple commands you can use ;, && and | Like this: killall Finder; killall SystemUIServer, cd ~/Desktop/ && rm Caches Or: man grep | man cat For example. But, is there a difference between |, ; and &&? If so, what is the difference?

In an answer to another very good question I made the following assertion: According to my reading of the POSIX specs, the use of one or the other makes no difference from a parsing standpoint. POSIX specifies that &&|| lists are compound commands which means that the entire list must be read i...

I would like to do something similar to the following: which someapplciation | cd outputfrompreviouscommand The command which provides a directory and I would like to be able to make that output my current working directory without using a programming language i.e. awk, bash, perl, etc. and to...

I am trying to understand how the logical operator precedence works in bash. For example, I would have expected, that the following command does not echo anything. true || echo aaa && echo bbb However, contrary to my expectation, bbb gets printed. Can somebody please explain, how can I make ...

In tutorials and how-to's I often see commands combined. For instance, sudo apt-get update && sudo apt-get install pyrenamer There seem to be four possible connectors: &, &&, || and ;. Though the & connector is clear to me (it sends a process to the background and leaves the terminal availabl...

You are using two different things here and should be using a third. Let's see: | : This is the pipe operator, it serves to pass the output of one process as input to another: foo | bar This runs the program foo and passes its output as input to the program bar. >,<,>> and <<: These are the ...

I'm trying to write a command that's a one-line for loop containing a command that uses the & operator to put the command in the background: for dir in $(ls); do command $dir &; done Where & tells BASH to run command in the background. Yet BASH returns bash: syntax error near unexpected tok...

How can one run multiple programs in the background with single command? I have tried the commands below, but they do not work. nohup ./script1.sh & && nohup ./script2.sh & -bash: syntax error near unexpected token '&&' nohup ./script1.sh & ; nohup ./script2.sh & -bash: syntax error near unexp...

WARNING DO NOT ATTEMPT TO RUN THIS ON A PRODUCTION MACHINE In reading the Wikipedia page on the topic I generally follow what's going on with the following code: :(){ :|:& };: excerpt of description The following fork bomb was presented as art in 2002;56 its exact origin is unknown, b...