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gawk: Printf Examples

 
 5.5.4 Examples Using 'printf'
 -----------------------------
 
 The following simple example shows how to use 'printf' to make an
 aligned table:
 
      awk '{ printf "%-10s %s\n", $1, $2 }' mail-list
 
 This command prints the names of the people ('$1') in the file
 'mail-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 }' mail-list
      -| Amelia     555-5553
      -| Anthony    555-3412
      -| Becky      555-7685
      -| Bill       555-1675
      -| Broderick  555-0542
      -| Camilla    555-2912
      -| Fabius     555-1234
      -| Julie      555-6699
      -| Martin     555-6480
      -| Samuel     555-3430
      -| Jean-Paul  555-2127
 
    In this case, the phone numbers had to be printed as strings because
 the numbers are separated by dashes.  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 a 'BEGIN' rule (⇒
 BEGIN/END) 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 }' mail-list
 
    The preceding example mixes '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 }' mail-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 }' mail-list
 
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