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Full Discussion: Scratching my head over old post
Top Forums Shell Programming and Scripting Scratching my head over old post Post 303003144 by apmcd47 on Friday 8th of September 2017 04:16:56 AM
Old 09-08-2017
Quote:
Originally Posted by OMLEELA
Hello !

Pondering over some old post & I need some help.

Questions -
1. In there , the magic is happening all because of $0=$2. Can someone please explain to me as to what does $0=$2 means ?
2. Also can someone go over the sed operation here as I tried to understand this for the past 2 hours and I am not getting anywhere with this.


best regards,
Lee.
In awk $0 refers to the whole record (line) while $1, $2 ... refer to the individual fields. So $0=$2 simply replaces the whole record with field 2.

In sed the (escaped) parentheses earmark part of a pattern for a later reference.

Take for instance this:
Code:
$ echo "charlie farley" | sed 's/\(charlie\) .*/\1 chaplin/'
charlie chaplin
$ echo "piggy malone" | sed 's/\(charlie\) .*/\1 chaplin/'
piggy malone

So basically I want to change "charlie farley" into "charlie chaplin" (or any other charlie) but leave anything else alone. I this extremely simple example I could have written
Code:
$ echo "charlie farley" | sed 's/charlie .*/charlie chaplin/'

But consider this
Code:
$ echo "charlie farley" | sed 's/\(charl.*\) .*/\1 chaplin/'

Now I can catch "charles" or "charley" too. More general.

The \1 refers to the first earmarked pattern. But what if I do two of them?
Code:
$ echo "Charles Chaplin" | sed 's/\(.*\) \(.*\)/\2, \1/'
Chaplin, Charles

This last example takes two strings separated by a space and reverses them, putting a comma between.

Hope that helps.

Andrew
 

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LEARN ABOUT MOJAVE

platform::shell

platform::shell(n)					       Tcl Bundled Packages						platform::shell(n)

__________________________________________________________________________________________________________________________________________________

NAME

       platform::shell - System identification support code and utilities

SYNOPSIS

       package require platform::shell ?1.1.4?

       platform::shell::generic shell
       platform::shell::identify shell
       platform::shell::platform shell
_________________________________________________________________

DESCRIPTION

       The platform::shell package provides several utility commands useful for the identification of the architecture of a specific Tcl shell.

       This  package  allows the identification of the architecture of a specific Tcl shell different from the shell running the package. The only
       requirement is that the other shell (identified by its path), is actually executable on the current machine.

       While for most platform this means that the architecture of the interrogated shell is identical to the architecture of  the  running  shell
       this  is  not generally true. A counter example are all platforms which have 32 and 64 bit variants and where a 64bit system is able to run
       32bit code. For these running and interrogated shell may have different 32/64 bit settings and thus different identifiers.

       For applications like a code repository it is important to identify the architecture of the shell which will  actually  run  the  installed
       packages, versus the architecture of the shell running the repository software.

COMMANDS

       platform::shell::identify shell
	      This command does the same identification as platform::identify, for the specified Tcl shell, in contrast to the running shell.

       platform::shell::generic shell
	      This command does the same identification as platform::generic, for the specified Tcl shell, in contrast to the running shell.

       platform::shell::platform shell
	      This command returns the contents of tcl_platform(platform) for the specified Tcl shell.

KEYWORDS

       operating system, cpu architecture, platform, architecture

platform::shell 						       1.1.4							platform::shell(n)
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