Hi,

The thing is that sometimes I need to filter an arbitrary output given a condition (think on the "filter" function present on some programming languages) from the shell (I use sh/bash). I tried this:

#!/bin/sh
# Usage: filter command [options_for_xargs]
COMMAND=$1
shift 1
xargs "$@" -I "{}" sh -c "if $COMMAND; then echo {}; fi"

$ find /etc -type f -print0 | filter "! test -x {}" -0
/etc/fam.conf
/etc/cups/cupsd.conf
/etc/cups/snmp.conf
/etc/cups/lpoptions
/etc/cups/mime.types
....

FWIW: find supports the -mode option - you use this to test permissions bits.

Your generic filter invokes a whole new process, which may not be all that efficient when compared to other options available to a command. It is an interesting idea, though. Have you considered the concept of a coprocess using named pipes?

See the bash FAQ here:
ftp://ftp.cwru.edu/pub/bash/FAQ

Yes, I'm aware of this, it was just an example.

Certaintly. A pure bash solution (less versatile as it does not use xargs) I though was as simple as:

#!/bin/sh
COMMAND=$1
while read LINE; do
     eval "${COMMAND/\{\}/$LINE}" && echo $LINE
done

Originally Posted by jim mcnamara Have you considered the concept of a coprocess using named pipes?

xargs "$@" -I "{}" echo "$COMMAND && echo {}" | sh

The FAQ shows you how to write coprocesses with named pipes.