Suppose you tried something like this:
$ paste ../data/file-{A,B,C}.dat
and realize that you want to sort each file (numerically, let's suppose) before pasting. Then, using process substitution, you need to write something like this:
$ paste <(sort -n ../data/file-A.dat) \
<(sort -n ../data/file-B.dat) \
<(sort -n ../data/file-C.dat)
Here you see a lot of duplication, which is not a good thing. Because each process substitution is isolated from one another, you cannot use any brace expansion or pathname expansion (wildcards) that spans multiple process substitution.
Is there a tool that allows you to write this in a compact way (e.g. by giving sort -n and ../data/file-{A,B,C}.dat separately) and composes the entire command line for you?
You could do:
eval paste '<(sort -n ../data/file-'{A,B,C}'.dat)'
Or to automate it as a function
sort_paste() {
local n i cmd
n=1 cmd=paste
for i do
cmd="$cmd <(sort -n -- \"\${$n}\")"
n=$(($n + 1))
done
eval "$cmd"
}
sort_paste ../data/file-{A,B,C}.dat
(in some ksh implementations, you need to replace local with typeset)
To adapt to any arbitrary command, (and to prove that eval can be safe when used properly), you could do:
xproc() {
local n i cmd stage stage1 stage2 stage3
cmd= xcmd= stage=1 n=1
stage1='cmd="$cmd \"\${$n}\""'
stage2='xcmd="$xcmd \"\${$n}\""'
stage3='cmd="$cmd <($xcmd \"\${$n}\")"'
for i do
if [ -z "$i" ] && [ "$stage" -le 3 ]; then
stage=$(($stage + 1))
else
eval 'eval "$stage'"$stage\""
fi
n=$(($n + 1))
done
eval "$cmd"
}
xproc paste '' sort -n -- '' ../data/file-{A,B,C}/dat
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