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= KEY CONCEPTS =
===Using the sed Utility===
'''Usage:'''
'''<span style="color:blue;font-weight:bold;font-family:courier;">Syntax: sed [-n] 'address instruction' filename</span>'''
'''How it Works:'''
* The sed command reads all lines in the input file and will be exposed to the expression<br>(i.e. area contained within quotes) one line at a time.
* The expression can be within single quotes or double quotes.
* The expression contains an address (match condition) and an instruction (operation).
* If the line matches the address, then it will perform the instruction.
* Lines will display be default unless the '''–n''' option is used to suppress default display
<br>
'''Address:'''
* Can use a line number, to select a specific line (for example: '''5''')
* Can specify a range of line numbers (for example: '''5,7''')
* Regular expressions are contained within forward slashes (e.g. /regular-expression/)
* Can specify a regular expression to select all lines that match a pattern (e.g '''/^[0-9].*[0-9]$/''')
* If NO address is present, the instruction will apply to ALL lines
[[Image:sed.png|right|500px|]]
'''Instruction:'''
*'''Action''' to take for matched line(s)
*Refer to table on right-side for list of some<br>'''common instructions''' and their purpose
<br><br>
===Using the awk Utility===
'''Usage:'''
<span style="color:blue;font-weight:bold;font-family:courier;">awk [-F] 'selection-criteria {action}’ file-name</span>
'''How It Works:'''
* The '''awk''' command reads all lines in the input file and will be exposed to the expression (contained within quotes) for processing.
*The '''expression''' (contained in quotes) represents '''selection criteria''', and '''action''' to execute contained within braces '''{}'''
* if selection criteria is matched, then action (between braces) is executed.
* The '''–F''' option can be used to specify the default '''field delimiter''' (separator) character<br>eg. '''awk –F”;”''' (would indicate a semi-colon delimited input file).
<br>
'''Selection Criteria'''
* You can use a regular expression, enclosed within slashes, as a pattern. For example: '''/pattern/'''
* The ~ operator tests whether a field or variable matches a regular expression. For example: '''$1 ~ /^[0-9]/'''
* The '''!~''' operator tests for no match. For example: '''$2 !~ /line/'''
* You can perform both numeric and string comparisons using relational operators ( '''>''' , '''>=''' , '''<''' , '''<=''' , '''==''' , '''!=''' ).
* You can combine any of the patterns using the Boolean operators '''||''' (OR) and '''&&''' (AND).
* You can use built-in variables (like NR or "record number" representing line number) with comparison operators.<br>For example: '''NR >=1 && NR <= 5'''
<br>
'''Action (execution):'''
* Action to be executed is contained within braces '''{}'''
* The '''print''' command can be used to display text (fields).
* You can use parameters which represent fields within records (lines) within the expression of the awk utility.
* The parameter '''$0''' represents all of the fields contained in the record (line).
* The parameters '''$1''', '''$2''', '''$3''' … '''$9''' represent the first, second and third to the 9th fields contained within the record.
* Parameters greater than nine requires the value of the parameter to be placed within braces (for example: '''${10}''','''${11}''','''${12}''', etc.)
* You can use built-in '''variables''' (such as '''NR''' or "record number" representing line number)<br>eg. '''{print NR,$0}''' (will print record number, then entire record).
= INVESTIGATION 1: USING THE SED UTILITY =