xargs jar tvf - does not work

Question

Objective: to list files in all jars.

This works:

for f in `find . -name "*.jar"`; do jar tvf $f; done

This works too:

find . -name "*.jar" -exec jar tvf {} \;

This does not (it does not print any output):

find . -name "*.jar" | xargs jar tvf

Why does the latter not work?

score 16 · Accepted Answer · answered Jul 07 '11 at 23:46

16

Does this works

find . -name "*.jar"|xargs -n 1 jar -tvf

answered Jul 07 '11 at 23:46

Rahul

Swiss · Answer 2 · 2019-07-30T19:03:02.990

9

The problem is that jar tvf only allows one file to be passed in.

The for loop runs the files one by one

jar tvf 1.jar; jar tvf 2.jar; ...

However, xargs tries to fit as many arguments on one line as possible. Thus it's trying the following:

jar tvf 1.jar 2.jar ...

You can verify this by placing an echo in your command:

for f in `find . -name "*.jar"`; do echo jar tvf $f; done
find . -name "*.jar" | xargs echo jar tvf

The proper solution is the tell xargs to only use one parameter per command:

find . -name "*.jar" | xargs -n 1 jar tvf

or

find . -name "*.jar" | xargs -I{} jar tvf {} # Find style parameter placement

edited Jul 30 '19 at 19:03

answered Jul 07 '11 at 23:50

Swiss

Thanks for the `-i` hint, nice. – sarnold Jul 08 '11 at 00:14
@sarnold you have to know that this argument (`-i`) is deprecated. see man xargs (`xargs (GNU findutils) 4.4.2`): `This option is deprecated; use -I instead.` There is no problem to use it in interactive mode but I would avoid it in scripts since it could disapear in a futur versions of xargs. – Lynch Jul 15 '11 at 01:46

score 6 · Answer 3 · answered Jul 07 '11 at 23:54

It does not work because xargs invoke only one process with all arguments.

There is a way to invoke a new process for each argument using -I'{}'.

Try this to understand:

$ seq 10 | xargs echo
1 2 3 4 5 6 7 8 9 10
$ seq 10 | xargs -I'{}' echo {}
1
2
3
4
5
6
7
8
9
10

3 Answers3