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Top Forums Shell Programming and Scripting How to detect empty field in awk ? Post 302793507 by Don Cragun on Friday 12th of April 2013 12:58:55 PM
Old 04-12-2013
If your fields are tab separated, you can use Yoda's solution if you change "|" both places where it appears in his script to "\t".
If fields are separated by a <space> or a mixture of <space> and <tab>, it isn't as easy to do it with awk because awk's default field separator (a space character) is interpreted to mean any combination of one or more space or tab characters.

If you really want to use a single space as your field separator, you could:
  1. look for a space at the start of a line and replace it with "BAD ",
  2. look for any occurrence of two spaces together and replace them with " BAD ", and
  3. look for a space at the end of a line and replace it with " BAD".

If you want to use every <space> or <tab> as a field separator, you could use the directions in the list above but use look for a space or tab every place where it currently says look for a space above and use look for any occurrence of a space or tab immediately followed by a space or tab where it currently says look for any occurrence of two spaces together. I will leave both of these options as an exercise for the reader.
 

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JOIN(1) 						      General Commands Manual							   JOIN(1)

NAME
join - relational database operator SYNOPSIS
join [ options ] file1 file2 DESCRIPTION
Join forms, on the standard output, a join of the two relations specified by the lines of file1 and file2. If file1 is `-', the standard input is used. File1 and file2 must be sorted in increasing ASCII collating sequence on the fields on which they are to be joined, normally the first in each line. There is one line in the output for each pair of lines in file1 and file2 that have identical join fields. The output line normally con- sists of the common field, then the rest of the line from file1, then the rest of the line from file2. Fields are normally separated by blank, tab or newline. In this case, multiple separators count as one, and leading separators are dis- carded. These options are recognized: -an In addition to the normal output, produce a line for each unpairable line in file n, where n is 1 or 2. -e s Replace empty output fields by string s. -jn m Join on the mth field of file n. If n is missing, use the mth field in each file. -o list Each output line comprises the fields specifed in list, each element of which has the form n.m, where n is a file number and m is a field number. -tc Use character c as a separator (tab character). Every appearance of c in a line is significant. SEE ALSO
sort(1), comm(1), awk(1) BUGS
With default field separation, the collating sequence is that of sort -b; with -t, the sequence is that of a plain sort. The conventions of join, sort, comm, uniq, look and awk(1) are wildly incongruous. JOIN(1)
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