02-23-2010
I'm trying to achieve the following goals:
1. Only read the log files from disk once.
2. Only decompress the log files once.
3. Process the log files with multiple parallel processes.
4. wait for them all to complete
5. do something else.
The reason being is that disk io and decompression are expensive in comparison to log processing, so I only want to do them once. And running the processing in parallel leverages my quad core processor to further reduce run time.
I think I have what I need, but I'm open to any other suggestions for how to do this better.
With background jobs method you suggest I would have to :
1. create an array of 6 unique temporary pipe names
2. mkfifo for each of the 6 pipes
3. start sending the decompressed logs to 6 named pipes using tee
4. launch a the 6 processing pipelines in the background telling them to read from the named pipes.
5. Now I could use wait to wait for them all.
6. rm all the temporary pipes
7. continue my script
This would work too, but is this better than using 'tee >(cmd1) >(cmd2)...>(cmd6)' and waiting for them to echo something into one named pipe that I have to manually manage? At least 'tee' takes care of creating and destroying the named pipes for me.
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LEARN ABOUT OPENDARWIN
subst
subst(n) Tcl Built-In Commands subst(n)
__________________________________________________________________________________________________________________________________________________
NAME
subst - Perform backslash, command, and variable substitutions
SYNOPSIS
subst ?-nobackslashes? ?-nocommands? ?-novariables? string
_________________________________________________________________
DESCRIPTION
This command performs variable substitutions, command substitutions, and backslash substitutions on its string argument and returns the
fully-substituted result. The substitutions are performed in exactly the same way as for Tcl commands. As a result, the string argument
is actually substituted twice, once by the Tcl parser in the usual fashion for Tcl commands, and again by the subst command.
If any of the -nobackslashes, -nocommands, or -novariables are specified, then the corresponding substitutions are not performed. For
example, if -nocommands is specified, command substitution is not performed: open and close brackets are treated as ordinary characters
with no special interpretation.
Note that the substitution of one kind can include substitution of other kinds. For example, even when the -novariables option is speci- |
fied, command substitution is performed without restriction. This means that any variable substitution necessary to complete the command |
substitution will still take place. Likewise, any command substitution necessary to complete a variable substitution will take place, even |
when -nocommands is specified. See the EXAMPLES below. |
If an error occurs during substitution, then subst will return that error. If a break exception occurs during command or variable substi- |
tution, the result of the whole substitution will be the string (as substituted) up to the start of the substitution that raised the excep- |
tion. If a continue exception occurs during the evaluation of a command or variable substitution, an empty string will be substituted for |
that entire command or variable substitution (as long as it is well-formed Tcl.) If a return exception occurs, or any other return code is |
returned during command or variable substitution, then the returned value is substituted for that substitution. See the EXAMPLES below. |
In this way, all exceptional return codes are ``caught'' by subst. The subst command itself will either return an error, or will complete |
successfully.
EXAMPLES
When it performs its substitutions, subst does not give any special treatment to double quotes or curly braces (except within command sub-
stitutions) so the script
set a 44
subst {xyz {$a}}
returns ``xyz {44}'', not ``xyz {$a}'' and the script |
set a "p} q {r" |
subst {xyz {$a}} |
return ``xyz {p} q {r}'', not ``xyz {p} q {r}''. |
When command substitution is performed, it includes any variable substitution necessary to evaluate the script. |
set a 44 |
subst -novariables {$a [format $a]} |
returns ``$a 44'', not ``$a $a''. Similarly, when variable substitution is performed, it includes any command substitution necessary to |
retrieve the value of the variable. |
proc b {} {return c} |
array set a {c c [b] tricky} |
subst -nocommands {[b] $a([b])} |
returns ``[b] c'', not ``[b] tricky''. |
The continue and break exceptions allow command substitutions to prevent substitution of the rest of the command substitution and the rest |
of string respectively, giving script authors more options when processing text using subst. For example, the script |
subst {abc,[break],def} |
returns ``abc,'', not ``abc,,def'' and the script |
subst {abc,[continue;expr 1+2],def} |
returns ``abc,,def'', not ``abc,3,def''. |
Other exceptional return codes substitute the returned value |
subst {abc,[return foo;expr 1+2],def} |
returns ``abc,foo,def'', not ``abc,3,def'' and |
subst {abc,[return -code 10 foo;expr 1+2],def} |
also returns ``abc,foo,def'', not ``abc,3,def''.
SEE ALSO
Tcl(n), eval(n), break(n), continue(n)
KEYWORDS
backslash substitution, command substitution, variable substitution
Tcl 7.4 subst(n)