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Linkoteca. bash

Running Bash commands in Python

Imago voragine.net
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To somewhat expand on the earlier answers here, there are a number of details which are commonly overlooked.

  • Prefer subprocess.run() over subprocess.check_call() and friends over subprocess.call() over subprocess.Popen() over os.system() over os.popen()
  • Understand and probably use text=True, aka universal_newlines=True.
  • Understand the meaning of shell=True or shell=False and how it changes quoting and the availability of shell conveniences.
  • Understand differences between sh and Bash
  • Understand how a subprocess is separate from its parent, and generally cannot change the parent.
  • Avoid running the Python interpreter as a subprocess of Python.

Push-button installer of macOS Catalina, Mojave, and High Sierra guests in Virtualbox

Imago voragine.net
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macos-guest-virtualbox.sh is a Bash script that creates a macOS virtual machine guest on VirtualBox with unmodified macOS installation files downloaded directly from Apple servers.

A default install only requires the user to sit patiently and, less than ten times, press enter when prompted by the script, without interacting with the virtual machine.

Tested on bash and zsh on Cygwin. Works on macOS, CentOS 7, and Windows on x86 CPUs with VT-x or AMD-V. Should work on most modern Linux distros.

macOS Catalina (10.15), Mojave (10.14), and High Sierra (10.13) currently supported.

git – getting ALL previous version of a specific file/folder

Imago voragine.net
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The script would:
– extract all file versions to /tmp/all_versions_exported
– take 1 argument – relative path to the file inside git repo
– give result filenames numeric prefix (sortable)
– mention inspected filename in result files (to tell apples apart from oranges:)
– mention commit date in the result filename (see output example below)
– not create empty result files

Shell parameter expansion: bash native regular expresssion for replacements

Imago voragine.net
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The ‘$’ character introduces parameter expansion, command substitution, or arithmetic expansion. The parameter name or symbol to be expanded may be enclosed in braces, which are optional but serve to protect the variable to be expanded from characters immediately following it which could be interpreted as part of the name.

When braces are used, the matching ending brace is the first ‘}’ not escaped by a backslash or within a quoted string, and not within an embedded arithmetic expansion, command substitution, or parameter expansion.

Create User Accounts with Random Password with a bash script

Imago voragine.net
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#!/bin/bash

####
# This script automatically creates user accounts with random passwords.
#
# Author: Russ Sanderlin
# Date: 01/21/15
#
###

if [ $# -lt 1 ]; then
echo "Please supply a user name"
echo "Example: " $0 "jsmith"
exit
fi

# Declare local variables, generate random password.

newuser=$1
randompw=$(cat /dev/urandom | tr -dc 'a-zA-Z0-9' | fold -w 8 | head -n 1)

# Create new user and assign random password.

useradd $newuser
echo $newuser:$randompw | chpasswd
echo "UserID:" $newuser "has been created with the following password:" $randompw