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I created a text file and put some email addresses in it. Then I used grep to find them. Indeed it worked:

# pattern="^[a-zA-Z0-9]+@[a-zA-Z0-9]+\.[a-z]{2,}"
# grep -E $pattern regexfile

but only as long I kept the -E option for an extended regular expression. How do I need to change the above regex in order to use grep without -E option?

share|improve this question
    
BTW, in case glenn’s O’Reilly reference elicits a TL;DR response, this regex is way short of what you need to match real-world email addresses; see Email Address Syntax at Wikipedia, for starters. –  Scott Apr 7 at 23:42
    
Your regex isn't even close to correct for email address. For example, it doesn't recognize [email protected]. Many other examples. –  Chris Johnson 13 hours ago

1 Answer 1

up vote 1 down vote accepted

Be aware that matching email addresses is a LOT harder that what you have. See an excerpt from the Mastering Regular Expressions book

However, to answer your question, for a basic regular expression, your quantifiers need to be one of *, \+ or \{m,n\} (with the backslashes)

pattern='^[a-zA-Z0-9]\+@[a-zA-Z0-9]\+\.[a-z]\{2,\}'
grep "$pattern" regexfile

You need to quote the pattern variable

share|improve this answer
    
why is it important to quote the variable ? –  Abdul Al Hazred Apr 7 at 20:55
    
The answer to that is spelled out in great detail here: unix.stackexchange.com/q/171346/4667 –  glenn jackman Apr 7 at 21:01

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