On 12Jan2012 19:07, Dean S. Messing <deanm@xxxxxxxxxxxxx> wrote:
| On 13 Jan 2012 at 13:55:27, Cameron Simpson wrote:
| <snip>
| > The:
| >
| > <foo command [args...]
| >
| > form is handy for programmatically constructed pipelines, too.
|
| Sorry, I don't understand "programmatically constructed pipelines".
| Would you elaborate? Thanks
Where one has a script that figures out a pipeline and assembles it.
So one might have a file conversion tool that goes:
my-convert-script src-file dst-file change1 change2 change3 ...
which goes:
src=$1; shift
dst=$2; shift
shcmd="<\"\$src\" cat"
for change
do
case "$change" in
a) conv="cmd-to-do-change-a" ;;
b) conv="some-other-command-to-do-change-b" ;;
esac
shcmd="$shcmd | $conv"
done
shcmd="$shcmd >\"\$dst\""
sh -c "$shcmd"
This builds a shell pipeline command, starting with the input
redirection, adding pipes to munge the data, then adding the output
redirection. (Obviously there's no error checking etc above, and the
"cat" can be optimised out, etc.)
Cheers,
--
Cameron Simpson <cs@xxxxxxxxxx> DoD#743
http://www.cskk.ezoshosting.com/cs/
And it is not our part here to take thought only for a season, or for a few
lives of Men, or for a passing age of the world. - Gandalf the grey
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