Why are these regular expressions different?
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I am looking for lines that have an apostrophe in them and tried a few expressions that seemed identical to me; however, some worked and others didn't. Why did I get the following behavior:

    egrep \' file      # works as expected

    egrep "\'" file    # seems to return all lines

    egrep "[\']" file  # works as expected

    egrep '\'' file    # seems to be waiting for more input