All About bash in 30 minutes

Short History

• bash descended from ksh and the "bourne shell". The word comes from "Bourne Again SHell".
  • Currently the default shell on Mac OS X

bash Basics

• Case Sensitive
  • Special Symbols and command lines: #, $, >, <.
• bash Quoting: ",', escapes, et cetera
  • Removing a file called "*"
• bash Variables
  • Process Scope ("Why isn't my symbol assigned?"), running from the "."
  • Special Variables: $PS1, ${1...}, $$, $HOSTNAME, $USER, $RANDOM
• Profile files
  • .bash_profile
  • $ENV
• Redirection: >,<, >&1 et al
• command line history and autocompletion
  • tab, uparrow..

Programming with bash

• When NOT to use bash: when the problem takes more than about 150 lines to solve
  • Scoping is crude at best
  • Not object-oriented
  • Easy to create wonderful, clever, hopelessly confusing code.
  • Slow
• Creating subroutines: foo() { }
• Symbol manipulation: ${bif:-} et cetera
• Control Flow and Loops: if then else fi, for in do done, while do done, esac
  • What used to be the test(1) program (aka "[")
• Arithmetic processing: "let" and (())
• Useful Vocabulary Words (programs): grep(1), awk(1), sed(1), tr(1), seq(1), nl(1), wc(1), find(1) et cetera
• Good practices IMNSHOP
  • Use "set -x" and script(1) for debugging
  • Make configuration files and write groups of short scripts, rather than one humongo unmaintainable wad of code
  • Delimiting variables: use full ${} notation to prevent interpreter from making surprising decisions about variable names
  • Use getopt(1), provide command-line help always