A twisted feature of sort when called in awk Post: 302377441

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Top Forums Shell Programming and Scripting A twisted feature of sort when called in awk Post 302377441 by nrgbooster on Friday 4th of December 2009 05:30:48 AM

12-04-2009

Registered User

A twisted feature of sort when called in awk

Hello,

In the book Classic Shell Scripting, there is an example showing how you can call a shell command through awk's pipe:

Code:

for (name in telephone){
    print name "\t" telephone[name] | "sort"
}
close("sort")

The output, as seen from the terminal, is perfectly the sorted list of name-tel pairs. Yet a result like such, however, is not theoretically expected. Since sort appears within the loop body, it should sort each time when a name-tel pair is printed. And thus it should have sorted nothing since the data are separatedly (pairwise) fed to it.

Searching throughout the network I found this:

Quote:

The sort could even be done from within the program:

Code:

sort = "sort -k 2nr"
for (word in freq)
    printf "%s\t%d\n", word, freq[word] | sort

close(sort)

This way of sorting must be used on systems that do not have true pipes at the command-line (or batch-file) level. See the general operating system documentation for more information on how to use the sort program.

But what does this explanation really mean?

Thanks for reading the thread, and please share your thoughts!

nrgbooster

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LEARN ABOUT MINIX

join

JOIN(1) 						      General Commands Manual							   JOIN(1)

NAME

       join - relational database operator

SYNOPSIS

       join [-an] [-e s] [-o list] [-tc] 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.

       -o list
	      Each output line comprises the fields specified 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.

7th Edition							  April 29, 1985							   JOIN(1)