Linux System Administration Recipes A Problem-Solution Approach

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CHAPTER 8 ■ USING THE COMMAND LINE BETTER26 cd ..27 }2829 for dir in $@; do30 rename_recursive "$dir"31 done3233 cd "$cwd"34 exit 0Lines 01–07 do the setup and check for at least one argument (the directory to iterate over), line 09records your current directory so you can get back there at the end, and line 10 assigns the argument to anamed variable. Lines 12–27 are the part that does the work. You cd into the directory given by theargument; then in line 15 you get a listing of that directory and iterate over each item in the listing. Inlines 16 and 17, you check whether that item is a directory, and if it is, you run the rename_recursivefunction on it—this is the recursive bit! Otherwise, in lines 19–23, you check to see whether the filenameends in .html and rename it to .shtml if so. Line 25 loops you back to line 15, and once we’ve dealt withall the items in the directory, you jump back up a directory, and the function is finished.Lines 29–31 do the initial calling of the function on each argument in turn (so the function will berun, recursively, on each directory you name on the command line), and line 33 makes sure you’vewound up back where you started.8-3. Implementing Programmable Completion with bashAnother trick you’ll already be familiar with is hitting Tab to autocomplete filenames and commands.This is great and a massive time-saver, but there are a few ways to extend it.The first tip isn’t, in fact, exactly extending autocompletion, but it helps you locate directories moreeasily. $CDPATH does for cd what $PATH does for executables. In other words, it’ll allow you to type just thename of a directory, and if the parent of that directory is in your $CDPATH, it’ll take you straight there. Itsaves having to type the full path each time.So, say you regularly want to go to the research subdirectory of your website at/local/www/html/research. Set your $CDPATH like this to include the parent directory:export CDPATH="/home/jkemp:/local/www/html/:$CDPATH"Now just type cd research to get to /local/www/html/research.However, with that setting, if you’re in ~/book/ and want to cd into the research-notes subdirectoryof that directory, you need to be wary. If you type research, hit Tab, and then hit Enter without payingattention, you’ll end up in /local/www/html/research by accident. In other words, $CDPATH overrides thedefault completion settings, which would otherwise just look in your current directory. To fix this, add(the current directory) to the start of the path:export CDPATH=".:/home/jkemp:/local/www/html/:$CDPATH"Now the current directory will be searched first, and then the other directories in the $CDPATH will besearched.176Download at WoweBook.Com
CHAPTER 8 ■ USING THE COMMAND LINE BETTER■ Note This won’t tab-complete. You’ll need to type the full directory name in (research, in this example), unlessyou’re cding to a directory in your current directory, in which case tab-complete functions as normal.However, the major improvement available for the regular autocompletion is programmablecompletion. This more or less borrows from zsh, which has extensive autocompletion and a few otherinteresting options (it should be available as a package for your distro if you want to investigate).You can write completion functions all by yourself, but to avoid extensive wheel reinvention, you’rebetter off downloading /etc/bash_completion from http://www.caliban.org/bash/ (also available as apackage for most distros and installed by default in Ubuntu as the bash-completion package and Debianin the bash package) and then sourcing that file in your ~/.bashrc file:source /etc/bash_completionNow open a new terminal window, and then try typing ssh at the command line and then hittingTab. You’ll be shown a list of possible hosts, based primarily on your known_hosts file (along with acouple of other tricks). Various other commands are also set up to do this by the /etc/bash_completionfile. Experiment with traceroute or ftp.You can also extend this particular form of completion to other commands or to your own scripts.Take a look at the /etc/bash_completion file. It’s pretty big, but you can see that there are a set ofsubroutines beginning with an underscore (for example, _known_hosts). These are the subroutines thatdo the work of figuring out the possible autocompletions. Search for a line that looks like this:complete -F _known_hosts traceroute ping telnet host sshcomplete -F identifies the function to use for completion. Anything returned by the function (here,known_hosts) is provided as a possible completion option for the commands listed after that function(here, traceroute ping telnet host ssh). -C is a similar option that executes a command and takes theoutput from that as possible completion. So, if you want to add your command to that list, just add it onthe end of this line and re-source the file:> vim /etc/bash_completioncomplete -F _known_hosts traceroute ping telnet host ssh mycommand> source /etc/bash_completionTest your command. It should now autocomplete with hostnames.■ Note In general, the functions in /etc/bash_completion fall back on the compgen bash built-in, which passesoptions to complete (another built-in) to try to generate a word completion. This is the “normal” tab-completionoption, but it’s quite limited for words such as hostnames using only the $HOSTFILE file, which will usually be/etc/hosts and which is very limited in modern systems that rely on external DNS.177Download at WoweBook.Com
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Contents■About the Author .......
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■ CONTENTS3-7. Writing a Nagios P
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■ CONTENTS■Chapter 8: Using the
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■ CONTENTSAbout the Author■Juli
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■ CONTENTSAcknowledgmentsMany tha
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■ CONTENTSIntroductionThis book i
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■ INTRODUCTIONDownloading the Cod
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C H A P T E R 1■ ■ ■Saving Yo
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CHAPTER 1 ■ SAVING YOURSELF EFFOR
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C H A P T E R 2■ ■ ■Centraliz
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CHAPTER 2 ■ CENTRALIZING YOUR NET
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C H A P T E R 3■ ■ ■Monitorin
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CHAPTER 3 ■ MONITORING AND UPDATI
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C H A P T E R 4■ ■ ■Taking Ba
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CHAPTER 4 ■ TAKING BACKUPS AND MA
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C H A P T E R 5■ ■ ■Working w
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CHAPTER 5 ■ WORKING WITH FILESYST
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CHAPTER 5 ■ WORKING WITH FILESYST
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Page 157 and 158: CHAPTER 6 ■ SECURING YOUR SYSTEMS
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Page 191 and 192: C H A P T E R 8■ ■ ■Making Be
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Page 225 and 226: CHAPTER 10 ■ THINGS GO IN, THINGS
Page 233 and 234: C H A P T E R 11■ ■ ■Tracking
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CHAPTER 11 ■ TRACKING DOWN BUGSAn
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CHAPTER 11 ■ TRACKING DOWN BUGS#
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C H A P T E R 12■ ■ ■Managing
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CHAPTER 12 ■ MANAGING TIME AND PE
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APPENDIX■ ■ ■Perl TipsSee rec
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APPENDIX ■ PERL TIPS• Date::Par
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APPENDIX ■ PERL TIPSPerl Syntax N
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■ ■ ■Index■Symbols$CDPATH,
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■ INDEXenscript option (printing)
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■ INDEX■NNagiosadding hosts to,
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■ INDEXsyslogcentralized logging
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