On Thu, 9 Dec 2010, Jan L. Peterson wrote:
> On Dec 9, 2010, at 1:57 PM, [email protected] wrote:
>
>> I have a situation where I have a bunch of config files that define
>> filters, I want to cat a file and run it through all these filters,
>> capturing the output
>>
>> the command line to do so would be something like:
>>
>> cat input |./filter1 -r file1 |./filter1 -r file2 |./filter2 -r file3 >output
>>
>> the following line produces a line that looks like this
>>
>> echo -n "cat input | "; ls *.meta |cut -f 1 -d "." |while read file; do grep
>> "^Filter: " $file.meta |head -1 |cut -f 2 -d " " |while read filter; do echo
>> -n "./$filter -r $file | "; done; done; echo "cat >output"
>
> Let me see if I understand what you're actually doing...
>
> You have a directory with a file "input" that contains some input and a bunch
> of files *.meta that each contain one or more lines that look like "Filter:
> something". The "something"s denote commands that accept a -r argument
> followed by the name of the meta file that defined it (without the .meta
> extension), which expect to read from stdin and write to stdout. You
> ultimately want the output of the last filter to land in a file called
> "output".
>
> Leaving aside your code for extracting the filenames and setting up the
> command, I think you want to use eval.
>
> eval `echo -n "cat input | "; ls *.meta |cut -f 1 -d "." |while read file; do
> grep "^Filter: " $file.meta |head -1 |cut -f 2 -d " " |while read filter; do
> echo -n "./$filter -r $file | "; done; done; echo "cat >output"`
thanks, that works.
> I'd suggest, however, something like this:
>
> (eval `ls -1 *.meta | while read m; do f=\`grep "^Filter:" $m | awk '{print
> $2; exit}'\`; echo -n "./$f -r \`basename $m .meta\` |"; done | sed -e
> "s/|$//"`) < input > output
>
> which gets rid of the multiple "cut" commands, "head", one of the nested
> loops, and both gratuitous uses of "cat".
basename to eliminate one cut is a good point (I know about the command,
but it's not something I commonly use), is it really any faster for this
(since they both need to execute a command)
but what happens if the grep "^Filter:" returns more than one item? won't
all of them become part of f?
David Lang
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