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Full Discussion: figuring out an awk one liner
Top Forums Shell Programming and Scripting figuring out an awk one liner Post 302640891 by benalt on Tuesday 15th of May 2012 12:01:06 PM
Old 05-15-2012
Thanks. I realize the result. I am trying to work out why. I know that $0 is being set to the last character because the field separator has been set to null and $0 is being set to the last field. But I am not used to the way it has been written (i.e. without {...} etc.). I presume it is outputting each record by default. I am still a little confused about this one liner. Any further clarification would be appreciated.

Thanks,
Ben

---------- Post updated at 10:51 AM ---------- Previous update was at 10:43 AM ----------

Quote:
Originally Posted by Corona688
That's an old-fasioned way of setting variables in awk. Setting a blank field-separator means, in some versions of awk, to split on every single character.
Ah. That was the main part which was puzzling me. Is it handled like doing a -vFS= and can this method of variable assignment be relied on for different platforms?

Thanks,
Ben

---------- Post updated at 11:01 AM ---------- Previous update was at 10:51 AM ----------

Quote:
Originally Posted by Corona688
I don't think this is a very efficient usage. Never use awk to process one single line if you can help it, that's lighting a furnace to burn a hair; modern enough shells have builtins which can do this without the overhead of running an entire process.
I agree. I know I can do this: echo ${STRING#${STRING%?}} or in ksh I can do: typeset -R1 c=$STRING; echo $c. Coming across this line in awk that I couldn't completely understand though bothered me.

Ben
 

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ipc::sysv5.18

IPC::SysV(3pm)						 Perl Programmers Reference Guide					    IPC::SysV(3pm)

NAME

       IPC::SysV - System V IPC constants and system calls

SYNOPSIS

	 use IPC::SysV qw(IPC_STAT IPC_PRIVATE);

DESCRIPTION

       "IPC::SysV" defines and conditionally exports all the constants defined in your system include files which are needed by the SysV IPC
       calls.  Common ones include

	 IPC_CREATE IPC_EXCL IPC_NOWAIT IPC_PRIVATE IPC_RMID IPC_SET IPC_STAT
	 GETVAL SETVAL GETPID GETNCNT GETZCNT GETALL SETALL
	 SEM_A SEM_R SEM_UNDO
	 SHM_RDONLY SHM_RND SHMLBA

       and auxiliary ones

	 S_IRUSR S_IWUSR S_IRWXU
	 S_IRGRP S_IWGRP S_IRWXG
	 S_IROTH S_IWOTH S_IRWXO

       but your system might have more.

       ftok( PATH )
       ftok( PATH, ID )
	   Return a key based on PATH and ID, which can be used as a key for "msgget", "semget" and "shmget". See ftok.

	   If ID is omitted, it defaults to 1. If a single character is given for ID, the numeric value of that character is used.

       shmat( ID, ADDR, FLAG )
	   Attach the shared memory segment identified by ID to the address space of the calling process. See shmat.

	   ADDR should be "undef" unless you really know what you're doing.

       shmdt( ADDR )
	   Detach the shared memory segment located at the address specified by ADDR from the address space of the calling process. See shmdt.

       memread( ADDR, VAR, POS, SIZE )
	   Reads SIZE bytes from a memory segment at ADDR starting at position POS.  VAR must be a variable that will hold the data read. Returns
	   true if successful, or false if there is an error. memread() taints the variable.

       memwrite( ADDR, STRING, POS, SIZE )
	   Writes SIZE bytes from STRING to a memory segment at ADDR starting at position POS. If STRING is too long, only SIZE bytes are used; if
	   STRING is too short, nulls are written to fill out SIZE bytes. Returns true if successful, or false if there is an error.

SEE ALSO

       IPC::Msg, IPC::Semaphore, IPC::SharedMem, ftok, shmat, shmdt

AUTHORS

       Graham Barr <gbarr@pobox.com>, Jarkko Hietaniemi <jhi@iki.fi>, Marcus Holland-Moritz <mhx@cpan.org>

COPYRIGHT

       Version 2.x, Copyright (C) 2007-2010, Marcus Holland-Moritz.

       Version 1.x, Copyright (c) 1997, Graham Barr.

       This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

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