Real programmers use programming languages (Not shell scripts)

Real programmers use programming languages (Not shell scripts)

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  Real Programmers Use ProgrammingLanguages (Not Shell Scripts) Daniel Laeng - May 2014 daniel@laeng.org
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  About Me I’m aprogrammer (not a sysadmin) ● I like simple, readable, well tested code ● My background: Ruby, Java, C, R, PHP, bash ● I try to use the right tool for the right job ● I have seen bad code in every language
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  (My) Definitions Shell Script ●Primarily used as command line interpreter ● Can also be used to write scripts/programs ● e.g. sh, csh, bash, tcsh, ksh, powershell ● Shell language of choice: bash Programming Language ● Primarily for writing programs ● Rich set of libraries ● Compiled or uncompiled ● e.g. C, C++, Java, Python, Ruby, Perl, PHP
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  Why Shell Scriptsare Good ● Quick to write ● Use commands you know (cp, mv, ps, etc) ● Complex tasks can be done in a short script ● Easy to try out on command prompt ● Power of unix pipes for free
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  Shell Programming Issues What’sbad about programming in shell scripts ● Confusing syntax ● Untyped (everything is a string) ● Slow ● Not always portable ● No exception handling
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  Confusing Syntax 1 Bash ●Outputs: “No” ● Comparison operator “>” does string comparison ● Should have used “-eq” instead
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  Confusing Syntax 2 ●Outputs: “No” ● Is actually a syntax error!! ● $A must be wrapped in double quotes
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  Confusing Syntax! ● Nonstandard comparison operators ● Variables need to be quoted... sometimes ● Variables need to be prepended with "$"... sometimes ● Syntax errors can be caused by variable contents
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  Untyped ● All variablesbehave like strings ● Some integer operations are allowed ● No built in floating point operators!! ● Can’t define your own types
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  Speed - Whichis faster? 18 seconds (touch is an external command) 1 second (echo is a bash builtin)
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  Slow ● Built incommands are very limited ● You must use external commands often ● External commands are SLOW ● Slow code is not obvious. This takes 6 seconds: ● Equivalent code takes 0.1 seconds in ruby
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  Not Reliably Portable Shellon my computer != Shell your computer ● ksh, tcsh and zsh are not common ● bash is common (but not universal) ● bourne shell (sh) is universal but weak ● None of them are likely to work on Windows ● Strong reliance on OS commands - which differ across computers
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  No Exception Handling ●There is no built in exception handling ● There are (complicated) ways to work around this ● Errors are hard to debug
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  When To UseShell Scripts Shell (Scripts) ● Working on the command line ● Wrapper to start a program ● One off hack to automate tedious task ● Keep it SHORT! (under 50 lines) Programming Languages ● Anything with complicated logic ● Anything that needs to be fast ● Anything that needs to be portable ● Anything that should be tested
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  Generic ● Python ● Ruby ●Perl What To Use Instead Building / Compiling ● Make ● Rake ● Ant ● Maven Deployment ● Capistrano ● Bamboo ● Jenkins ● Chef / Puppet Dev-Ops ● Chef ● Puppet ● Vagrant
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  Conclusions Understand your tools ●Shell scripts are very useful ● But - they are not a replacement for programming languages ● Think about your choice - pick the right tool ● Happy scripting