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Full Discussion: Scripts dont give a consistent output..
Top Forums UNIX for Beginners Questions & Answers Scripts dont give a consistent output.. Post 302981434 by bakunin on Tuesday 13th of September 2016 03:30:17 AM
Old 09-13-2016
Quote:
Originally Posted by wisecracker
However the 'IFS' reason is new to me and would like to know more so thanks a lot. Off to look...
The "internal field separator" is a shell variable which tells the shell how separate "words" (=input fields) are separated from each other. Consider this command:

Code:
command arg1 arg2 arg3

Somehow the shell has to know why this is to parse as a call to "command" with three different arguments, "arg1", "arg2" and "arg3". The reason is that in fact the command looks (for the shells parser) like this:

Code:
<string1><IFS><string2><IFS><string3><IFS><string4>

and because the default value for IFS is a space the shell sees four strings, of which the first is a command and the others are arguments. This is why you have to quote "words" (commands, arguments) containing spaces: quotes turn off the mechanism inside them.

Still you can redefine this IFS to split "words" at other boundaries than the usual spaces. Consider the following input file:

Code:
word1 word2, word3 word4, word5 word6 
bla,1 bla,2 bla,3 bla,4 bla,5 bla,6

Now execute the following command (ksh, change "print -" to "echo" for bash):
Code:
while read w1 w2 w3 w4 w5 w6 ; do
     print - "w1: \"$w1\""
     print - "w2: \"$w2\""
     print - "w3: \"$w3\""
     print - "w4: \"$w4\""
     print - "w5: \"$w5\""
     print - "w6: \"$w6\""
done < ifs

Now change the while-line to:
Code:
while IFS=, read w1 w2 w3 w4 w5 w6 ; do

and run again to see the difference.

I hope this helps.

bakunin
 

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LEARN ABOUT OSX

pwd

PWD(1)							    BSD General Commands Manual 						    PWD(1)

NAME

     pwd -- return working directory name

SYNOPSIS

     pwd [-L | -P]

DESCRIPTION

     The pwd utility writes the absolute pathname of the current working directory to the standard output.

     Some shells may provide a builtin pwd command which is similar or identical to this utility.  Consult the builtin(1) manual page.

     The options are as follows:

     -L      Display the logical current working directory.

     -P      Display the physical current working directory (all symbolic links resolved).

     If no options are specified, the -L option is assumed.

ENVIRONMENT

     Environment variables used by pwd:

     PWD  Logical current working directory.

EXIT STATUS

     The pwd utility exits 0 on success, and >0 if an error occurs.

SEE ALSO

     builtin(1), cd(1), csh(1), sh(1), getcwd(3)

STANDARDS

     The pwd utility conforms to IEEE Std 1003.1-2001 (``POSIX.1'').

BUGS

     In csh(1) the command dirs is always faster because it is built into that shell.  However, it can give a different answer in the rare case
     that the current directory or a containing directory was moved after the shell descended into it.

     The -L option does not work unless the PWD environment variable is exported by the shell.

BSD
								  April 12, 2003							       BSD
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