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Full Discussion: Problems understanding pipes
Top Forums Programming Problems understanding pipes Post 302562724 by ab_tall on Friday 7th of October 2011 09:08:25 PM
Old 10-07-2011
Ok, I went the other way round,

I implemented all builtins first, thinking I could use them as needed in my pipes.
I tried to mesh that in with the prev eg. which you gave of the IPC via pipes. But then I need to create 2 versions of my builtins,

if the builtin is the 1st command in the pipe, it's executed in the same shell,
if the builtin is somewhere in the middle,
then it needs to be executed in a separately forked process => that the builtin needs to have a corresponding external command for exec to work.

i.e
Code:
if( piped commands)
{
if(isbuiltin())
{
execbuiltin() // function where i implemented all builtins.
squirt into the first pipe
}
else
{
exec as in your sample prev.
(here it fails as that code would need me to exec an external command always - which may or may not exist)
}
}

Perhaps, i need to rethink my approach.
 

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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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