11-26-2012
p1 is used to store the value of the first field. Since this is done at the end of each line processing, it becomes the previous value of the first field for the current line.
Quote:
Is prev a built-in variable?
No. In
awk, the built-in variables are all upper-case words.
prev is used to store the line made up by appending segments of the lines which have common first fields. After printing each made-up line, we need to nullify the variable to make it ready for the next line to be made up.
And the cryptic line does what you thought it does. If
prev"" (
prev is not-null) is true, then we must be having at least 1 line in
prev so we need to append a
, (
FS - field separator, comma in this case, and that's a special/built-in
awk variable) and the substring of the line from the second field onwards. Else if
prev is null, then it must be the first time since printing the last
prev. So, just assign the current line (
$0) to
prev.
And, I think you've understood rest of the things.
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prev(1) General Commands Manual prev(1)
NAME
prev - show the previous message (only available within the message handling system, mh)
SYNOPSIS
prev [+folder] [-[no]header] [-help] [-showproc program] [-noshowproc] [options to showproc]
OPTIONS
Displays a one-line header before the message. The header consists of the name of the folder and the message number. This is the default
behavior. It can be suppressed with the -noheader option. Prints a list of the valid options to this command. Specifies an alternative
program to list messages. The default is to use the program defined by the showproc: entry in the file. As with show, you can give options
to the showproc program at the command line. These are passed directly to showproc by prev.
The defaults for this command are:
+folder defaults to the current folder -header
DESCRIPTION
The prev command displays the previous message in the current folder. The previous message is the one before the current message in the
folder. The message that is shown becomes the current message.
You can specify a folder other than the current folder by using the +folder argument. If you specify a folder, that becomes the current
folder.
RESTRICTIONS
The prev command is really a link to the show program. As a result, if you make a link to prev and that link is not called prev, your link
will act like show instead. To avoid this, add a profile-entry for the link to your MH profile and add the argument prev to the entry.
PROFILE COMPONENTS
Path: To determine your Mail directory
showproc: Program to show the message
EXAMPLES
The command in the following example displays the previous message in the folder +copylog: $ prev +copylog
FILES
The user profile.
SEE ALSO
show(1), next(1)
prev(1)