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Full Discussion: get data
Top Forums UNIX for Dummies Questions & Answers get data Post 302592182 by rbatte1 on Monday 23rd of January 2012 06:45:55 AM
Old 01-23-2012
So the code supplied:-
Code:
cut -f2,4 -d"\"" filename | tr "\"" " "

If you are not familiar then it probably looks a bit serious. We'll break it down. The vertical bar, known as a pipe mark, joins the output from one operation to the input of the next operation. In this way, you can string a number of processes together. It saves you having to write an output file with each operation to then be read in by the next. All processing happens in memory so saving the I/O effort and time.

From this, you can see you have two statements joined up. The first part reads the file filename and slices it up. The flags on the cut command give the instructions. -d tells cut what the delimiter is (how to count along fields in a record). In our case, we're counting by a " however as this is a special character to we have to mark it as such with an Escape character. The blackslash \ tells the shell not to interpret the " and just pass it as it is into the cut command. If we didn't do this, it would try to interpret the -d flag as open-double-quote, close-double-quote (so nothing), open double-quote, space, filename and then get very confused because it's only expecting a single character. You would probably get an error for ending on an open-double-quote andyway as it will be waiting for the next double-quote to make a valid statement.
The -f2,4 states that we want fields 2 & 4 only.

Slightly annoyingly, this uses the existing delimited of " to separate the fields in the output, so we pass this as input to the tr command with the pipe. The tr command is a character translator. It has two parameters in out case, a double quote and a space. It simply reads all the input then passes it as output converting every occurrence of the double quote into a space.

That is how you generate the output in the format you require.



Does that explain it properly? I've never been a good teacher, so please feel free to complain or ask more questions about it.




Robin
Liverpool/Blackburn
UK
 

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LEARN ABOUT MOJAVE

page_util_quote

page_util_quote(n)					      Parser generator tools						page_util_quote(n)

__________________________________________________________________________________________________________________________________________________

NAME

       page_util_quote - page character quoting utilities

SYNOPSIS

       package require page::util::quote  ?0.1?

       package require snit

       ::page::util::quote::unquote char

       ::page::util::quote::quote'tcl char

       ::page::util::quote::quote'tclstr char

       ::page::util::quote::quote'tclcom char

_________________________________________________________________

DESCRIPTION

       This package provides a few utility commands to convert characters into various forms.

API

       ::page::util::quote::unquote char
	      A  character,  as stored in an abstract syntax tree by a PEG processor (See the packages grammar::peg::interpreter, grammar::me, and
	      their relations), i.e. in some quoted form, is converted into the equivalent Tcl character. The character is returned as the  result
	      of the command.

       ::page::util::quote::quote'tcl char
	      This command takes a Tcl character (internal representation) and converts it into a string which is accepted by the Tcl parser, will
	      regenerate the character in question and is 7bit ASCII. The string is returned as the result of this command.

       ::page::util::quote::quote'tclstr char
	      This command takes a Tcl character (internal representation) and converts it into a string which is accepted by the Tcl  parser  and
	      will generate a human readable representation of the character in question.  The string is returned as the result of this command.

	      The  string  does not use any unprintable characters. It may use backslash-quoting. High UTF characters are quoted to avoid problems
	      with the still prevalent ascii terminals. It is assumed that the string will be used in a double-quoted environment.

       ::page::util::quote::quote'tclcom char
	      This command takes a Tcl character (internal representation) and converts it into a string which is accepted by the Tcl parser  when
	      used within a Tcl comment. The string is returned as the result of this command.

BUGS, IDEAS, FEEDBACK
       This  document,	will  undoubtedly  contain  bugs  and  other  problems.  Please report such in the category page of the Tcllib SF Trackers
       [http://sourceforge.net/tracker/?group_id=12883].  Please also report any ideas for enhancements you may have.

KEYWORDS

       page, parser generator, quoting, text processing

CATEGORY

       Page Parser Generator

COPYRIGHT

       Copyright (c) 2007 Andreas Kupries <andreas_kupries@users.sourceforge.net>

page									1.0							page_util_quote(n)
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