bash.adoc

bash

Shell modes

A login shell is one whose first character of argument zero is a -, or one started with the --login option. An interactive shell is one started without non-option arguments and without the -c option.

Basically, when login from a tty you get an interactive login shell. When opening a terminal from within X, you get just an interactive shell.

The last type of shell, is the shell you get within a script.

Interactive login shell files

Login

1. /etc/profile

   and then, in order of precedence, just the first readable file found is executed:

2. ~/.bash_profile

3. ~/.bash_login

4. ~/.profile

Logout

1. ~/.bash_logout

Interactive non login shell files

1. /etc/bash.bashrc

2. ~/.bashrc

Command line editing

Deleting

Delete to end of line	Ctrl + k
Delete to start of line	Ctrl + u
Delete to start of word	Ctrl + w
Delete to end of word	Alt + d

Moving

Go to the start	Ctrl + a
Go to the end	Ctrl + e
Go to next word (forward)	Alt + f
Go to previous word (backward)	Alt + b

Aliases

Aliases is an easy way to alias commands to keywords. For instance:

alias ll='ls -al'

But aliases cannot accept arguments. A workaround is to define as alias a function and invoke it:

alias sshls='function _sshls() { ssh $1 "ls -al";};_sshls'

and with sshls hostname the output of ls -al on the remote host is displayed.

Scripting

To exit script on error add the following:

set -e

In case of a command that returned non-true (0), script execution is stopped.

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To exit your script if you try to use an uninitialised variable add the following:

set -u

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Exercises

• Print 1000 random numbers in the range 1..1000, sort them, eliminate duplicates and take the first 100

(for i in {1..1000}; do shuf -i 1-1000 -n1; done;) | sort -nu | head -n100