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Full Discussion: Numeric computations in bash
Top Forums UNIX for Dummies Questions & Answers Numeric computations in bash Post 302622421 by jim mcnamara on Thursday 12th of April 2012 06:43:41 AM
Old 04-12-2012
In shell code you are concerned about: efficiency and readability
The former because you want to minimize the impact of your code on the system, the latter because you and others will have to change this stuff X years from now when you have completely forgotten about it, and it no longer works the way you need.

Either of these is equally fast:
Code:
a=$b
((a=b))

The first one is more conventional, and is more likely to port.

[ is a bash builtin, [[ is a keyword so they both run as part of the shell, as does (( )).
So it boils down to which one is the easiest to for another person to interpret, which is a personal matter.
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RBASH(1)						      General Commands Manual							  RBASH(1)

NAME
rbash - restricted bash, see bash(1) RESTRICTED SHELL
If bash is started with the name rbash, or the -r option is supplied at invocation, the shell becomes restricted. A restricted shell is used to set up an environment more controlled than the standard shell. It behaves identically to bash with the exception that the follow- ing are disallowed or not performed: o changing directories with cd o setting or unsetting the values of SHELL, PATH, ENV, or BASH_ENV o specifying command names containing / o specifying a file name containing a / as an argument to the . builtin command o specifying a filename containing a slash as an argument to the -p option to the hash builtin command o importing function definitions from the shell environment at startup o parsing the value of SHELLOPTS from the shell environment at startup o redirecting output using the >, >|, <>, >&, &>, and >> redirection operators o using the exec builtin command to replace the shell with another command o adding or deleting builtin commands with the -f and -d options to the enable builtin command o using the enable builtin command to enable disabled shell builtins o specifying the -p option to the command builtin command o turning off restricted mode with set +r or set +o restricted. These restrictions are enforced after any startup files are read. When a command that is found to be a shell script is executed, rbash turns off any restrictions in the shell spawned to execute the script. SEE ALSO
bash(1) GNU Bash-4.0 2004 Apr 20 RBASH(1)
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