Linux System Administration Recipes A Problem-Solution Approach

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CHAPTER 9 ■ WORKING WITH TEXT IN FILES# extended LDIF## LDAPv3# base with scope subtree# filter: (uid=jkemp)# requesting: ALL## jkemp, People, example.comdn: uid=jkemp,ou=People,dc=example,dc=comIf you want to do something with the information, it would be beneficial to lose at least those firsteight lines. This command will do that:ldapsearch "(uid=testuser)" | sed 1,8dThe syntax for a range is [first-line-#],[last-line-#].sed’s main power is in its regular expressions. To delete all lines that start with #, use this:ldapsearch "(uid=testuser)" | sed '/^#/d'The /pattern/ syntax is used to match regular expressions. ^ represents the start of the line. To alsoremove all the blank lines, use this:ldapsearch "(uid=testuser)" | sed '/^#/d' | sed '/^$/d'$ represents the end of the line, so here the pattern looked for is a line whose start and end havenothing between them.9-2b. Substitutionssed becomes more useful when you start using its editing capacity to edit within lines. The basic syntaxfor doing this is as follows:sed -e 's/foo/bar/g' filename.txtThis will replace all occurrences of foo in filename.txt with bar. The g means that the change ismade globally. Without it, only the first occurrence in each line will be edited.This syntax can be incredibly powerful, because you can use regular expressions and backreferences with it. For example, say that you use server-side includes in your web pages, so you have lotsof lines that look like this in your web site files for various values of filename (header, footer, and so on):However, for the local/directory of the web tree, you now want to use a different set of includes, soyou want to change filename.shtml to filename-local.shtml in all the files in this directory. This sed linewill do the trick:sed -i.bak 's/includes\/$\w*$.shtml/includes\/\1-local.shtml/' local/*.html188Download at WoweBook.Com
CHAPTER 9 ■ WORKING WITH TEXT IN FILESThe -i.bak edits the file in place, as shown previously. This will also keep a filename.bak backupcopy of the original file; to omit this, just use -i. The matched brackets $ and $ mark off the backreferences. So, the first section looks for the following and then saves filename as the first back reference:includes/filename.shtmlThe forward slash has to be escaped with a backslash (thus \/) to avoid it being interpreted as theterminator of the search pattern. \w is any word character (alphanumerics plus underscore), and \w*means any number of word characters, terminated with .shtml. See Table 9-1 for a quick description ofregexp syntax in sed.In the second half of the substitution, \1 refers to the first back reference (the file name). So, asrequired, you get filename.shtml being replaced with filename-local.shtml. Note that you don’t havethe g option at the end, because there should be only one file name per include line.■ Note To make the forward and backward slashes a little less confusing here, you can use another character forthe search/replace delimiter, such as s###g instead of s///g. So, the previous command line would become thefollowing:sed -i.bak 's#includes/$\w*$.shtml#includes/\1-local.shtml#' local/*.htmlTable 9-1. sed Regexp SyntaxCharacterDescription. Any character on the input line.^Doesn’t match a character but represents the start of the line.$ Doesn’t match a character but represents the end of the line.\ Use to escape special meaning. \. means a literal ., and \/ means aliteral /. Use to mark off a back reference in the first part of the expression.\n (where n is a number 1–9) The nth back reference in the previous part of the expression (see theprevious table entry and main recipe), as in \1.exp*Zero or more strings matching the expression exp (so A* matches zeroor more A characters).189Download 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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C H A P T E R 6■ ■ ■Securing
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Page 191 and 192: C H A P T E R 8■ ■ ■Making Be
Page 193 and 194: CHAPTER 8 ■ USING THE COMMAND LIN
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Page 223 and 224: C H A P T E R 10■ ■ ■Things G
Page 225 and 226: CHAPTER 10 ■ THINGS GO IN, THINGS
Page 233 and 234: C H A P T E R 11■ ■ ■Tracking
Page 235 and 236: CHAPTER 11 ■ TRACKING DOWN BUGSTh
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Page 251 and 252: C H A P T E R 12■ ■ ■Managing
Page 253 and 254: CHAPTER 12 ■ MANAGING TIME AND PE
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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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Linux System Administration Recipes A Problem-Solution Approach

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