Tuesday, July 9, 2013

cut command

The cut command takes a vertical slice of a file, printing only the specified columns or fields. Like the sort command, the cut command defines a field as a word set off by blanks, unless you specify your own delimiter. It's easiest to think of a column as just the n th character on each line. In other words, "column 5" consists of the fifth character of each line. Consider a slight variation on the company.data file we've been playing with in this section:

If you want to print just columns 1 to 6 of each line (the employee serial numbers), use the -c1-6 flag, as in this command:

cut -c1-6 company.data

If you want to print just columns 4 and 8 of each line (the first letter of the department and the fourth digit of the serial number), use the -c4,8 flag, as in this command:

cut -c4,8 company.data

And since this file obviously has fields delimited by colons, we can pick out just the last names by specifying the -d:and -f3 flags, like this:

cut -d: -f3 company.data

It's often the case that you want to use a space as the delimiter. To do so, you must put the delimiter in single quotes, like this: -d' '

Also, when you want to cut from a starting point to the end of the line, just leave off the final field number, as shown in the example below.

Let's say this is your test.txt file:
abc def ghi jkl
mno pqr stu vwx
yz1 234 567 890

To cut only columns 2-END, do this: cut -d' ' -f2- test.txt

And the results are:
def ghi jkl
pqr stu vwx
234 567 890

Here is a summary of the most common flags for the cut command:

-c [n | n,m | n-m] Specify a single column, multiple columns (separated by a comma), or range of columns (separated by a dash).
 [n | n,m | n-m] Specify a single field, multiple fields (separated by a comma), or range of fields (separated by a dash).
c Specify the field delimiter.
 Suppress (don't print) lines not containing the delimiter.

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