Forget Shell Scripts

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Forget Shell Scripts!
Mike Schilli, 06/16/2008 Yahoo!
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Overview

• Pros and cons of shell/Perl scripts
• How to whip up Perl scripts like Shell scripts
• How to create reusable scripts in Perl

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Where Shell Scripts shine

• Fast to whip up
• Running virtually everywhere (if you stick to
  /bin/sh syntax)

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Where Shell Scripts shine

• Dont need to quote strings
• Dont need to separate arguments by commas
• Shell cmd a b
• Perl cmd(a, b)

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Where Shell Scripts shine

• Dont need to quote strings
• Dont need to separate arguments by commas
• Shell cmd a b
• Perl sub cmd
• cmd a, b

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Where Shell Scripts Suck

• Can be written nicely, but mostly arent (see
  autoconf)
• Modularity
• Debugging
• Logging
• No CPAN to share stuff with
• Speed (interpreted line by line)

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Where Shell Scripts Suck

• Horrid syntax pitfalls
• var foo
• echo var

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Where Shell Scripts Suck

• Horrid syntax pitfalls
• var -n woah!
• echo var

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Where Shell Scripts Suck

• Horrid syntax pitfalls
• var -n woah!
• echo Xvar sed s/X//
• (Source Gnu Autoconf, Automake, and Libtool,
  Chapter 21, Writing portable bourne shell)

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Shell Programming gone wild!!!
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Shell Programming gone wild!!!
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Challenges with Perl Scripts

• Dont run everywhere
• but Linux distros come with perl already
• but there might be missing CPAN modules
• Lots of typing (open/read/close, error handling)

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Reusable one-off Perl scripts

• !/usr/local/bin/perl
• use SysadmInstall qw(cp)
• cp foo, bar

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Reusable one-off Perl scripts

• !/usr/local/bin/perl w
• use strict
• use SysadmInstall qw(cp)
• cp foo, bar

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Reusable one-off Perl scripts

• !/usr/local/bin/perl
• use SysadmInstall qw(all)
• cp foo, bar
• mv bar, baz

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SysadmInstall commands

• cp (copy)
• mv (move)
• untar (tar zxf )
• slurp (file to string)
• blurt (string to file)
• cd (with cdback())
• make (call make)

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SysadmInstall commands

• Run a shell command
• (stdout, stderr, rc)
• tap ls, -R

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SysadmInstall commands

• In-place-edit of a file
• pie sub s/foo/bar/ _ ,
• file.dat
• Process a file
• plough
• sub print if /foobar/ ,
• file.dat

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SysadmInstall commands

• answer ask Proceed, y
• Proceed y?
• picked pick prompt, \_at_choices, 3
• 1 Foo
• 2 Bar
• 3 Baz
• What now 3?

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SysadmInstall commands

• rmf()
• mkd()
• perm_set()
• perm_get()

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Enable Logging

• /usr/local/bin/perl w
• use strict
• use SysadmInstall qw(cp)
• use LogLog4perl (easy)
• LogLog4perl-gteasy_init(DEBUG)
• cp foo, bar
• cp abc, xyz
• my s slurp foo.dat

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Enable Logging (output)

• foo-script
• 2008/06/10 014814 cp abc def
• 2008/06/10 014814 cp ghi jkl
• 2008/06/10 014814 slurp foo.dat param1 123\n
  param10 345

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Raising errors by default (shell)

• /bin/sh
• cp foo bar
• cp abc xyz

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Raising errors by default

• /usr/local/bin/perl w
• use strict
• use SysadmInstall qw(cp)
• cp foo, bar fails
• cp abc, xyz
• foo-script
• Cannot copy abc to def (No such file or
  directory) at foo-script line 4

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Keep it Clean

• Exporting all vs. just what you need
• use SysadmInstall qw(all)
• use SysadmInstall (cp untar)

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Install on Debian

• apt-get install libsysadm-install-perl

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Additional Development Tips
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Use main()

• Make a script reusable, put your code in main()
• sub main
• some_function(a)
• some_other_funtion(b)

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Use main()

• Make a script reusable
• script1
• main() if !caller()
• sub main some_function()
• sub some_function
• 1

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Use main()

• Make a script reusable
• script1
• main() if !caller()
• sub main some_function()
• sub some_function
• 1
• Somewhere else
• other script
• require ./script1
• some_function()

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Refactor

• If a script turns out useful, refactor it to a
  module
• Use functions to encapsulate
• Add quick docs (use templates)
• Re-write the script to test the new module
• Push to CPAN if useful

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Get started quickly with new scripts

• tmpl do-this-task
• tmpl p MyTask.pm
• tmpl pm FullyQualified
• http//perlmeister.com/scripts/downloadl/tmpl
• Use vim shortcuts

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Portability tricks

• PAR creates portable module bundles
• PARPacker creates self-contained executables
• pp o fooscript.exe fooscript
• pp M IOZlib o foo.exe foo
• Caveat Same architecture
• Similar systems Use oldest to compile

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The End

• Proudly wear your Say No To /bin/sh logo ?

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The End

• Thanks!

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The End

• Slides http//perlmeister.com/talks.html