Silas Sewell - Bash

String Slicing in Bash (like Python)

silas — Thu, 12 Mar 2009 00:00:00 GMT

A simple function to slice strings in Bash similar to Python's string slicing functionality.

Examples

[silas@pluto ~]$ string_slice "12345" 0 1
1
[silas@pluto ~]$ string_slice "12345" 0 3
123
[silas@pluto ~]$ string_slice "12345" 2 3
3
[silas@pluto ~]$ string_slice "12345" 2 -2
3
[silas@pluto ~]$ string_slice "12345" -3
345

Implementation

function string_slice {
    STRING="$1"
    declare -i LENGTH="${#STRING}"
    declare -i START="$2"
    declare -i END="$3"
    if [ $START -lt 0 ]; then
        START=$[ $LENGTH + $START ]
    fi
    if [ $END -le 0 ]; then
        END=$[ $LENGTH + $END ]
    fi
    START=$[ $START + 1 ]
    (echo "$STRING" | cut -c $START-$END) 2> /dev/null
}

Profile Management with Git and GitHub

silas — Sun, 08 Mar 2009 00:00:00 GMT

The following describes a simple way to manage you profile configuration files using GitHub.

Features

Centralized configuration management
Files live in their native locations (no symbolic linking)
Home directory is not a Git repository
All the power of git with a simple alias

Setup Repository

Log into GitHub and create a repository named config
Add your public keys to GitHub (if you haven't done so already)
Open a terminal and switch to your home directory
```
cd ~
```
Create a configuration directory
```
mkdir .config.git
```

Add the following alias to your current session and your .bash_profile

alias config='git --git-dir=$HOME/.config.git/ --work-tree=$HOME'
echo "alias config='git --git-dir=$HOME/.config.git/ --work-tree=$HOME'" >> .bash_profile

Add your .bash_profile to the configuration repository
```
config add .bash_profile
```
Commit the changes
```
config commit -m 'Initial commit'
```

Change the origin to GitHub

config remote add origin git@github.com:GITHUB_USERNAME/config.git

Push the changes
```
config push origin master
```

If you get an error when running config pull to the effect of You asked me to pull without... run the follow:

    echo -e '[branch "master"]\n  remote = origin\n  merge = refs/heads/master' >> ~/.config.git/config

Setup Configuration Management on a Different System

Add your public keys to GitHub (if you haven't done so already)
Switch to your home directory
```
cd ~
```
Backup your local configuration files, example:
```
mv .bash_profile .bash_profile.bk
```

Clone your configuration repository

git clone git@github.com:GITHUB_USERNAME/config.git config.git

Move the git metadata to ~/.config.git
```
mv config.git/.git .config.git
```
Enable dotglob
```
shopt -s dotglob
```
Move your configuration files to your home directory
```
mv -i config.git/* .
```
Delete the config.git directory
```
rmdir config.git
```
Logout and log back in

Basic Usage

config pull - get latest configuration changes
config add FILENAME - add a configuration file
config commit -a - save all configuration changes
config push - push configuration changes to GitHub
and any other config GIT_OPTION

You can see my configuration repository at http://github.com/silas/config.

Source: Manage your $HOME with git by Robert Escriva

IPython + Python: Single Bash Command

silas — Mon, 01 Dec 2008 00:00:00 GMT

The following is a simple Bash function you can paste into your bashrc file to start Python/IPython depending on the context.

~/.bashrc

function python {
    IPYTHON="/usr/bin/ipython"
    PYTHON="/usr/bin/python"

    if [[ -n $1 ]]; then
        $PYTHON $@
    elif [[ -e $IPYTHON ]]; then
        $IPYTHON
    else
        $PYTHON
    fi
}

Simple Shell Script to Manage SSH Tunnels

silas — Sat, 15 Dec 2007 00:00:00 GMT

Manage SSH Tunnel is a simple shell script to start and stop ssh tunnels from the terminal.

Setup

Note: the setup assumes bash as the default shell

Download tunnel.sh and save it to ~/bin/

Add to ~/.bash_profile or ~/.bashrc

alias tunnel_home='/bin/sh ~/bin/tunnel.sh example.net sam 22 8888'

Replace example.net with the hostname of the server, sam with the username on the server, and 8888 with the local tunnel port
Type source ~/.bash_profile or source ~/.bashrc

Usage

To open the tunnel
```
tunnel_home start
```
To close the tunnel
```
tunnel_home close
```