Node:Printf Examples, Previous:Format Modifiers, Up:Printf

Examples Using printf

The following is a simple example of how to use printf to make an aligned table:

awk '{ printf "%-10s %s\n", $1, $2 }' BBS-list

This command prints the names of the bulletin boards ($1) in the file BBS-list as a string of 10 characters that are left-justified. It also prints the phone numbers ($2) next on the line. This produces an aligned two-column table of names and phone numbers, as shown here:

$ awk '{ printf "%-10s %s\n", $1, $2 }' BBS-list
-| aardvark   555-5553
-| alpo-net   555-3412
-| barfly     555-7685
-| bites      555-1675
-| camelot    555-0542
-| core       555-2912
-| fooey      555-1234
-| foot       555-6699
-| macfoo     555-6480
-| sdace      555-3430
-| sabafoo    555-2127

In this case, the phone numbers had to be printed as strings because the numbers are separated by a dash. Printing the phone numbers as numbers would have produced just the first three digits: 555. This would have been pretty confusing.

It wasn't necessary to specify a width for the phone numbers because they are last on their lines. They don't need to have spaces after them.

The table could be made to look even nicer by adding headings to the tops of the columns. This is done using the BEGIN pattern (see The BEGIN and END Special Patterns) so that the headers are only printed once, at the beginning of the awk program:

awk 'BEGIN { print "Name      Number"
             print "----      ------" }
     { printf "%-10s %s\n", $1, $2 }' BBS-list

The above example mixed print and printf statements in the same program. Using just printf statements can produce the same results:

awk 'BEGIN { printf "%-10s %s\n", "Name", "Number"
             printf "%-10s %s\n", "----", "------" }
     { printf "%-10s %s\n", $1, $2 }' BBS-list

Printing each column heading with the same format specification used for the column elements ensures that the headings are aligned just like the columns.

The fact that the same format specification is used three times can be emphasized by storing it in a variable, like this:

awk 'BEGIN { format = "%-10s %s\n"
             printf format, "Name", "Number"
             printf format, "----", "------" }
     { printf format, $1, $2 }' BBS-list

At this point, it would be a worthwhile exercise to use the printf statement to line up the headings and table data for the inventory-shipped example that was covered earlier in the section on the print statement (see The print Statement).