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Full Discussion: New to Linux scripting question
Top Forums UNIX for Dummies Questions & Answers New to Linux scripting question Post 302943679 by Don Cragun on Monday 11th of May 2015 07:45:42 PM
Old 05-11-2015
In standards conforming shells $((expression)) is known as an Arithmetic Expansion. The expression is evaluated, and the value of that expression is returned as the output from the expansion. The modulo operator (%) is a binary operator that returns the integer remainder obtained when dividing the first given operand by the second given operand. For example $((5 % 2)) will return 1 because 5 divided by 2 is 2 with the remainder 1 and $((6 % 2)) will return 0 because 6 divided by 2 is 3 with the remainder 0.

For more details on the expressions that can be processed in an arithmetic expansion, look at the bash man page on your system and search for Arithmetic Expansion.
 

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LEARN ABOUT FREEBSD

ddb

DDB(8)							    BSD System Manager's Manual 						    DDB(8)

NAME

     ddb -- configure DDB kernel debugger properties

SYNOPSIS

     ddb capture [-M -core] [-N -system] print
     ddb capture [-M -core] [-N -system] status
     ddb script scriptname
     ddb script scriptname=script
     ddb scripts
     ddb unscript scriptname
     ddb pathname

DESCRIPTION

     The ddb utility configures certain aspects of the ddb(4) kernel debugger from user space that are not configured at compile-time or easily
     via sysctl(8) MIB entries.

     To ease configuration, commands can be put in a file which is processed using ddb as shown in the last synopsis line.  An absolute pathname
     must be used.  The file will be read line by line and applied as arguments to the ddb utility.  Whitespace at the beginning of lines will be
     ignored as will lines where the first non-whitespace character is '#'.

OUTPUT CAPTURE

     The ddb utility can be used to extract the contents of the ddb(4) output capture buffer of the current live kernel, or from the crash dump of
     a kernel on disk.	The following debugger commands are available from the command line:

     capture [-M core] [-N system] print
	     Print the current contents of the ddb(4) output capture buffer.

     capture [-M core] [-N system] status
	     Print the current status of the ddb(4) output capture buffer.

SCRIPTING

     The ddb utility can be used to configure aspects of ddb(4) scripting from user space; scripting support is described in more detail in
     ddb(4).  Each of the debugger commands is available from the command line:

     script scriptname
	     Print the script named scriptname.

     script scriptname=script
	     Define a script named scriptname.	As many scripts contain characters interpreted in special ways by the shell, it is advisable to
	     enclose script in quotes.

     scripts
	     List currently defined scripts.

     unscript scriptname
	     Delete the script named scriptname.

EXIT STATUS

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

EXAMPLES

     The following example defines a script that will execute when the kernel debugger is entered as a result of a break signal:

	   ddb script kdb.enter.break="show pcpu; bt"

     The following example will delete the script:

	   ddb unscript kdb.enter.break

     For further examples, see the ddb(4) and textdump(4) manual pages.

SEE ALSO

     ddb(4), textdump(4), sysctl(8)

HISTORY

     The ddb utility first appeared in FreeBSD 7.1.

AUTHORS

     Robert N M Watson

BUGS

     Ideally, ddb would not exist, as all pertinent aspects of ddb(4) could be configured directly via sysctl(8).

BSD
								 December 24, 2008							       BSD
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