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?

  • 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 '15 at 23:42
  • 2
    Your regex isn't even close to correct for email address. For example, it doesn't recognize fred-smith@company.com. Many other examples. – Chris Johnson Sep 19 '15 at 18:45

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)

grep "$pattern" regexfile

You need to quote the pattern variable

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