Changes

In this section, you will learn how to use '''extended regular expressions ''' to help refine your search when using regular expressions.

# Issue the following linux pipeline command to download another data file called '''numbers2.dat''':<br><span style="color:blue;font-weight:bold;font-family:courier;">wget <nowiki>https://ict.senecacollege.ca/~murray.saul/uli101/numbers2.dat</nowiki></span><br><br>

# Issue the following linux pipeline command to display only whole numbers (with or without a positive or negative sign):<br><span style="color:blue;font-weight:bold;font-family:courier;">grep "^[+-]*[0-9][0-9]*$" numbers2.dat | more</span><br><br>You should notice multiple + or - signs are appearing as well. This occurs since you are searching or one or MORE occurrences of a + or - sign.<br>Using '''extended regular expression''' symbols to specify minimum and maximum repetitions '''{min,max}''' can solve this problem.<br><br># Issue the following linux pipeline command (using extended regular expression symbols) to display only whole numbers (with or without a positive or negative sign):<br><span style="color:blue;font-weight:bold;font-family:courier;">grep "^[+-]{0.1}[0-9]{1,}$" numbers2.dat | more</span><br><br>'''NOTE:''' most likely, there were '''NO results'''. This is due to the fact that the '''grep command was NOT issued correctly to use extended regular expression symbols'''. You would need to issue either '''grep -E''' (or more simply) issue the '''egrep''' command. The egrep command works with all regular expression symbols, and should be used in the future instead of the older grep command.<br><br># Reissue the above pipeline command using '''egrep''' instead of ''grep'':<br><span style="color:blue;font-weight:bold;font-family:courier;">egrep "^[+-]{0,1}[0-9]{1,}$" numbers2.dat | more</span><br><br>You should have noticed that the command worked correctly this time because you used the '''egrep''' command.<br><br># Issue the following linux pipeline command to display signed, unsigned, whole, and decimal numbers:<br><span style="color:blue;font-weight:bold;font-family:courier;">egrep "^[+-]{0,1}[0-9]{1,}[.]{0,1}[0-9]*$" numbers2.dat | more</span><br><br>You can also use extended regular expression symbols for '''grouping'''. For example, you can search for repetitions of GROUPS of characters<br>(like a word) as opposed to just a single character or a GROUP of numbers as opposed to a single digit.<br><br># Issue the following linux pipeline command to download another data file called '''words.dat''':<br><span style="color:blue;font-weight:bold;font-family:courier;">wget <nowiki>https://ict.senecacollege.ca/~murray.saul/uli101/words.dat</nowiki></span><br><br>

# Issue the following linux pipeline command to display two or more occurrences of the word "the":<br><span style="color:blue;font-weight:bold;font-family:courier;">egrep -i "(the){2,}" words.dat | more</span><br><br>'''NOTE:''' You should NOT see any output due to the fact that a <u>space </u> should be included at the end of the word "'''the'''". Usually words are separated by spaces; therefore, there were no matches since there were not occurrences of "thethe" as opposed to "'''the the'''"(i.e. no space after repetition of the pattern).<br><br># Reissue the previous pipeline command including a space in brackets:<br><span style="color:blue;font-weight:bold;font-family:courier;">egrep -i "(the ){2,}" words.dat | more</span><br><br>The "|" (or ) symbol | can be used within the grouping regular expression symbol symbols to allow matching of additional groups of characters. <br>Again, it is important to follow the character groupings with the space character<br><br># Issue the following linux pipeline command to search for 2 or more occurrences of the word "'''the'''" <u>or </u> the word "'''and'''":<br><span style="color:blue;font-weight:bold;font-family:courier;">egrep -i "(the |and ){2,}" words.dat | more</span><br><br>