safe-pipe

#!/bin/sh

# This guarantees that piping data through a command which might fail
# is equivalent to piping it through cat (i.e. untouched), rather than
# just losing the data.  E.g.:
#    
#    wget -o- http://foo.bar/baz.html | \
#      safe-pipe riskily-munge-HTML | grep foo
#
# Its Achilles' heel is that it assumes the filter will always play nice
# and return a non-zero exit code on failure, i.e. iff no output was generated.

tmp=`mktemp /tmp/safe-pipe.XXXXXXXXX`
cat >> $tmp

# FIXME: save output of risky filter somewhere and only do cat if
# non-zero exit code *and* no output was generated.  Otherwise we
# could get two lots of output.  Though maybe that's what we want
# in some circumstances?
"$@" < $tmp || cat $tmp

rm $tmp