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Full Discussion: CUT Command and grep issue
Top Forums Shell Programming and Scripting CUT Command and grep issue Post 302619527 by Corona688 on Thursday 5th of April 2012 03:35:31 PM
Old 04-05-2012
In principle it's relatively simple. It reads lines one by one, splits it into tokens, and runs the code you give it for each individual line. So '{ print $8 }' gets run for each individual line, printing the 8th column.

You can also tell it to run a code block only when a condition happens, like:

Code:
#Whenever the first column is ASDF, print the 8th column
awk '$1 == "ASDF" { print $8 }' filename

# Whenever the regex /ASDF/ matches the entire line, print the 8th column
awk '/ASDF/ { print $8 }'

You can also use variables, and even arrays, and especially, associative arrays -- arrays which can use strings as indexes. A["slartibartfast"]=32; print A["slartibartfast"] would print 32 for instance.

You can have more than one code block which runs under different conditions. You could use this to find only unique values in a column:
Code:
# For each line, set A["first column"]=1.
# Once all processing is done, print every array index.
awk '{ A[$1]=1 } END { for(X in A) print X }' file

And it's configurable, too. Usually, spaces and newlines are used to separate columns and lines, but it can use whatever you want instead! Lots of possibilities from a few simple rules.

P.S: $ is an operator, not a variable. $1 is column 1. You can also use it on a variable: N=5; print $N that would use the value of N to select column 5.
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PDOSTATEMENT.FETCHCOLUMN(3)						 1					       PDOSTATEMENT.FETCHCOLUMN(3)

PDOStatement::fetchColumn - Returns a single column from the next row of a result set

SYNOPSIS
public mixed PDOStatement::fetchColumn ([int $column_number]) DESCRIPTION
Returns a single column from the next row of a result set or FALSE if there are no more rows. Note PDOStatement.fetchColumn(3) should not be used to retrieve boolean columns, as it is impossible to distinguish a value of FALSE from there being no more rows to retrieve. Use PDOStatement.fetch(3) instead. PARAMETERS
o $column_number - 0-indexed number of the column you wish to retrieve from the row. If no value is supplied, PDOStatement.fetchColumn(3) fetches the first column. RETURN VALUES
PDOStatement.fetchColumn(3) returns a single column in the next row of a result set. Warning There is no way to return another column from the same row if you use PDOStatement.fetchColumn(3) to retrieve data. EXAMPLES
Example #1 Return first column of the next row <?php $sth = $dbh->prepare("SELECT name, colour FROM fruit"); $sth->execute(); print("Fetch the first column from the first row in the result set: "); $result = $sth->fetchColumn(); print("name = $result "); print("Fetch the second column from the second row in the result set: "); $result = $sth->fetchColumn(1); print("colour = $result "); ?> The above example will output: Fetch the first column from the first row in the result set: name = lemon Fetch the second column from the second row in the result set: colour = red SEE ALSO
PDO.query(3), PDOStatement.fetch(3), PDOStatement.fetchAll(3), PDO.prepare(3), PDOStatement.setFetchMode(3). PHP Documentation Group PDOSTATEMENT.FETCHCOLUMN(3)
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