using Regex and linux commands(grep or egrep?) to find specific strings -

note: not sure regex's correct since textbook @ school not explain/teach regex's of form of math form such dfa's/nfa

i appreciate suggestions or hints

question:

(a) find occurrences of 3 letter words in text begin `a' , end 'e';

(b) find occurrences of words in text begin `m' , end 'r';

my approach:

a) ^[a][a-za-z][e]$ (how distinguish between 3 letter words , words?)

b) ^[m][a-za-z][r]$

also want use these regex's in linux following command work?:

grep '^[a][a-za-z][e]$' 'usr/dir/.../text.txt'

or should use egrep in way:

find . -text "*.txt" -print0 | xargs -0 egrep '^[a][a-za-z][e]$'

you can use word boundary \b match start , end of word:

a) find occurrences of 3 letter words in text begin `a' , end 'e';

grep -o '\ba[a-za-z]e\b'

the pattern matches word boundary, following a, single character , following e , word boundary.

b) find occurrences of words in text begin `m' , end 'r';

grep -o '\bm[a-za-z]*r\b'

the pattern matches word boundary, m 0 ore more characters (thorugh * quantifier), r , word boundary again.

further i'm using options -o outputs every match on own line rather outputting whole line of input contains match.

btw, option -w - matching whole words - can simplify above patterns to:

grep -wo 'a[a-za-z]e'

and b)

grep -wo 'm[a-za-z]*r'

thanks @anubhava!

you asked egrep. egrep can't simplify or optimize patterns. grep absolutely fine.

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