Confusion about xargs...

[qwertygeek]

So.. I thought I understood how xargs worked for the most part, but it seems I don't as well as I thought. Why does:

find (foo) | cut (fields and delimter)

give me exactly what I expect, the files the find execution turned up, trimmed by whatever the cut command specifies, but

find (foo) | xargs -0 -I NAME cut NAME (fields and delimeter)

goes all sorts of wonky? I was under the impression xargs took the lhs of the pipe and rather than passing it to the rhs as one single large argument handed it over in sequence, akin to a loop, to escape the argument list size limitation?

A more specific example I guess would be something like..

find . -maxdepth 1 -name "*.cpp"

will turn up a series of .cpps in the current dir.. then say you want to trim out the middle (for whatever reason, bear with me, I'm making this up as I go)

find . -maxdepth 1 -name "*.cpp" | cut -f2 -d'.'

THAT works. But I can't make an xargs command out of it. I thought it would be something akin to:

find . -maxdepth 1 -name "*.cpp" | xargs -0 -I FILE cut FILE -f2 -d'.'

Where FILE would be replaced with the values retrieved by find. But creating a few random cpps right now and trying it I get:

cut: ./foo.cpp
./bar.cpp
./cutcutcut.cpp
./main.cpp
: No such file or directory

Am I missing something? This approach works for just about every other instance I've used xargs for before, but I'm starting to wonder if that was just by coincidence and I've totally understood it wrong this entire time...?

[drl]

Hi.

You know something about xargs, so I don't think I'll need to explain this:

#!/usr/bin/env bash

# @(#) s1	Demonstrate xargs.

# Infrastructure details, environment, commands for forum posts. 
echo
set +o nounset
LC_ALL=C ; LANG=C ; export LC_ALL LANG
echo "Environment: LC_ALL = $LC_ALL, LANG = $LANG"
echo "(Versions displayed with local utility \"version\")"
c=$(  ps | grep $$ | awk '{print $NF}' )
version >/dev/null 2>&1 && s=$(_eat $0 $1) 
[ "$c" = "$s" ] && p="$s" || p="$c"
version >/dev/null 2>&1 && version "=o" $p xargs
set -o nounset
echo

# Create a few files.

FILES="a.cpp b.cpp c.cpp"
rm -f $FILES
touch $FILES
ls -lgG $FILES

echo
echo " Results:"
find . -maxdepth 1 -name "*.cpp" | cut -f2 -d'.'

echo
echo " Results:"
find . -maxdepth 1 -name "*.cpp" | xargs

echo
echo " Results:"
find . -maxdepth 1 -name "*.cpp" | xargs cut -f2 -d. 

echo
echo " Results:"
find . -maxdepth 1 -name "*.cpp" | xargs -I FILE echo FILE | cut -f2 -d. 

exit 0

producing:

% ./s1

Environment: LC_ALL = C, LANG = C
(Versions displayed with local utility "version")
OS, ker|rel, machine: Linux, 2.6.26-2-amd64, x86_64
Distribution        : Debian GNU/Linux 5.0 
GNU bash 3.2.39
xargs (GNU findutils) 4.4.0

-rw-r--r-- 1 0 Jan 23 12:04 a.cpp
-rw-r--r-- 1 0 Jan 23 12:04 b.cpp
-rw-r--r-- 1 0 Jan 23 12:04 c.cpp

 Results:
/c
/b
/a

 Results:
./c.cpp ./b.cpp ./a.cpp

 Results:

 Results:
/c
/b
/a

Best wishes ... cheers, drl

[qwertygeek]

You.. might need to explain a LITTLE. Like I said, I'm starting to think my understanding of xargs wasn't as good as I thought before, so let me ask this: why does echoing the names over to cut work, while strictly passing the names to xargs fails?

[drl]

Hi.

Suppose there is only one file, "t1.cpp".

What is the difference between:

cut -f2 -d"." t1.cpp

and

echo t1.cpp | cut -f2 -d"."

Does

cut t1.cpp -f2 -d"."

make any sense?
cheers, drl

[qwertygeek]

Ah.. yes.. that does make a bit more sense now.. the issue was more with cut than xargs XD Thanks, appreciate it.

[drl]

Hi.

You're welcome. I think you would have gotten the solution by yourself, but a hint sometimes helps ... cheers, drl