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Full Discussion: Does awk have parameter substitution?
Top Forums Shell Programming and Scripting Does awk have parameter substitution? Post 302942848 by Scrutinizer on Saturday 2nd of May 2015 02:11:24 AM
Old 05-02-2015
Quote:
Originally Posted by RudiC
[..]

As to what pertains to the "double quoted emptyness", awk can't differentiate between empty and unset. But, neither can bash (man bash):
Code:
${parameter:-word}
Use Default Values. If parameter is unset or null, the expansion of word is substituted. Otherwise, the value of parameter is substituted.

Also from man bash:

Quote:
... bash tests for a parameter that is unset or null; omitting the colon results in a test only for a parameter that is unset.
So to test for an unset variable, use:
Code:
${parameter-word}

Which is also standard for any POSIX-conformant shell..

--
Regarding awk, it can detect set or unset array elements through the relational expression "element in array", where the element does not get created...

With regular variables, it is not so much that awk cannot detect unset variables, but rather - as a design choice - awk works such, that referencing a variable creates it first with an empty value.
Last edited by Scrutinizer; 05-02-2015 at 05:31 AM..
This User Gave Thanks to Scrutinizer For This Post:
RudiC
 

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LEARN ABOUT DEBIAN

dpkg-awk

DPKG-AWK(1)						      General Commands Manual						       DPKG-AWK(1)

NAME

       dpkg-awk - Utility to read a dpkg style db file

SYNOPSIS

       dpkg-awk [(-f|--file) filename] [(-d|--debug) ##] [(-s|--sort) list] [(-rs|--rec_sep) ??] '<fieldname>:<regex>' ... -- <out_fieldname> ..

DESCRIPTION

       dpkg-awk  Parses  a  dpkg status file (or other similarly formatted file) and outputs the resulting records.  It can use regex on the field
       values to limit the returned records, it can also be told which fields to output, and it can sort the matched fields.

OPTIONS

       -f filename
       --file filename
	      The file to parse.  The default is /var/lib/dpkg/status.

       -d [#]
       --debug [#]
	      Each time this is specified, it increased the debug level.

       -s field(s)
       --sort field(s)
	      A space or comma separated list of fields to sort on.

       -n field(s)
       --numeric field(s)
	      A space or comma separated list of fields that should be interpreted as numeric in value.

       -rs ??
       --rec_sep ??
	      Output this string at the end of each output paragraph.

       -h
       --help Display some help.

       fieldname
	      The fields from the file, that are matched with the regex given.	The fieldnames are case insensitive.

       out_fieldname
	      The fields from the file, that are output for each record.  If the first field listed begins with ^, then the list  of  fields  that
	      follows will NOT be output.

BUGS

       Be  warned  that  the author has only a shallow understanding of the dpkg packaging system, so there are probably tons of bugs in this pro-
       gram.

       This program comes with no warranties.  If running this program causes fire and brimstone to rain down upon the earth, you will be on  your
       own.

       This program accesses the dpkg database directly in places, querying for data that cannot be gotten via dpkg.

AUTHOR

       Adam Heath <doogie@debian.org>

DEBIAN
								 Debian Utilities						       DPKG-AWK(1)
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