CIS 218 Advanced UNIX1 Advanced UNIX CIS 218 Advanced UNIX Regular Expressions

CIS 218 Advanced UNIX2 Why Regular Expressions? v To locate text v To change text v v To delineate metacharacters from ordinary characters v v To suppress evaluation of metacharacters by the shell v v Different from filename expansion rules

CIS 218 Advanced UNIX3 vi Commands using Strings  /text search forward for text  :s/old/new/g replace every occurrence of old by new  :1,.s/fc/function/g fc replaced by function between line 1 and current

CIS 218 Advanced UNIX4 StringsExamples /ring/ring, spring, ringing /Thurs/Thursday, Thursday’s /or not/poor nothing

CIS 218 Advanced UNIX5 Regular Expressions (REs) v A RE is a string with special characters that defines one or more strings.  Special characters in vi :. [...](with - and ^) * ^ and $ \

CIS 218 Advanced UNIX6 ‘.’ Special Character v matches any single character REExamples /.ing/singing, ping /.alk/will talk, may balk

CIS 218 Advanced UNIX7 ‘[...]’ Special Characters v Match any single character given inside the brackets: i.e. [aeiou] is any single vowel –‘-’ to specify a range –‘^’ to make the range negative (this meaning for ‘^’ only applies inside [...]) v ‘\’, ‘*’, ‘$’ loose their special character meaning

CIS 218 Advanced UNIX8 REExamples /[bB]ill/bill, Bill, billed /t[aeiou].k/talkative, stink, teak, tanker /number [6-9]/number 60, number 8:, get number 9 /[^a-zA-Z]/1, }, Stop!

CIS 218 Advanced UNIX9 ‘*’ Special Character v Match 0 or more occurrences of a character REExamples /ab*c/ac, abc, abbc, debbcaabbbc /ab.*c/abc, abxc, ab45c, xab x cat /[a-zA-Z ]*/1. any string without nums or punctuation!

CIS 218 Advanced UNIX10 Longest Match Possible REExamples /(.*)/Get (this) and (that); /([^)]*)/Get (this) and (that); /s.*ing/singing songs, singing more

CIS 218 Advanced UNIX11 ‘^’ and ‘$’ Special Characters v ‘^’ matches a string at the beginning of a line v ‘$’ matches a string at the end of a line

CIS 218 Advanced UNIX12 REExamples /^T/This line..., That Time..., In Time /^+[0-9]/ , +759 Keep this... /:$/...below:...:+++:

CIS 218 Advanced UNIX13 ‘\’ Special Character v ‘\’ can be used to quote a special character to make it represent itself: \\\*\.etc.

CIS 218 Advanced UNIX14 REExamples /end\./The end., send., /\\/\ /\*/an asterisk (*) /\[5\]/it was five [5] /and\/or/and/or

CIS 218 Advanced UNIX15 Use of REs in grep v Put RE in single quotes ‘...’: $ grep ‘st.ing’ file $ grep ‘ooo*’ file $ grep ‘^T’ file $ grep ‘foo[0-9]’ file

CIS 218 Advanced UNIX16 Full (Extended) Regular Expressions v Default on most current UNIX versions  Extended form of RE used by egrep (and some other commands) The additional special characters: v +?| v Can use ‘+’, ‘?’, and ‘*’ with parentheses (...)

CIS 218 Advanced UNIX17 ‘+’ Special Character v Matches 1 or more occurrences of a character REExamples ‘ab+c’yabcw, abbc57 ‘(ab)+c’zabcd, ababc! v longest match possible rule applies!

CIS 218 Advanced UNIX18 ‘?’ Special Character v Matches 0 or 1 occurrences of a character REExamples ‘ab?c’back, abcdef ‘(ab)?c/xc, abcc

CIS 218 Advanced UNIX19 ‘|’ Special Character v means ‘or’; used between two REs REExamples ‘ab|ac’ab, ac, abac ‘^Exit|^Quit’Exit..., Quit..., No Exit ‘(D|N)\. Jones’P.D. Jones, N. Jones

CIS 218 Advanced UNIX20 RegEx Examples v v cats: cat cattle catalog scrawny cat vacation wildcat v (each on a separate line) v grep ca cats v grep cat cats v grep cat? cats v grep cat. cats v grep a cats v grep -v tt fruits v grep ^c cats v grep ‘t$' cats v grep '^' cats v v

CIS 218 Advanced UNIX21 RegEx Examples v Fruits: apple orange pear peach grape banana blueberry plum (each on a separate line) v grep pear fruits v grep ea fruits v grep a fruits v grep -v a fruits v grep ^p fruits.txt v grep 'e$' fruits.txt v grep '^' fruits.txt