I ran into a situation where I was piping the output of compgen -G to xargs basename and could not get it to work until I added the xargs -I parameter as seen below. Here is a script demonstrating what I was trying to do, with explanatory comments. I have two questions, and they appear after the script.

# create three files for testing:
touch /tmp/my.file.1.2.txt
touch /tmp/1.my.file.2.txt
touch /tmp/1.2.my.file.txt

# create a glob and verify that it works with compgen:
compgen -G "$glob"


# try to get the basename of each file using xargs.
# I thought this would work, but it does not.
compgen -G "$glob" | xargs basename

basename: extra operand ‘/tmp/my.file.1.2.txt’
Try 'basename --help' for more information.

# eventually I discovered that this would work.
# however, I don't understand why this would work
# but the previous attempt would not, since I
# think that this command is just a more
# explicitly-specified version of the previous 
# one.
compgen -G "$glob" | xargs -I{} basename {}


Other commands work with xargs without the -I parameter. For example, compgen -G "$glob" | xargs ls -al works just fine.

Question 1: What is it about basename in this script that requires the -I parameter?

Question 2: Until observing this result, I would have thought that xargs basename and xargs -I{} basename {} were synonyms of each other, but obviously they are not. What is the difference?

I doubt that it matters, but just in case: this is occurring on bash 5.0.17(1)-release running on Ubuntu 20.04.4 (5.13.0-35-generic).

I know there are other ways to generate this list of files, but I am concerned because I am clearly not understanding something fundamental here that I need to understand in order to avoid errors in the future.

1 Answer 1


POSIX basename only handles one name at a time, optionally with a suffix to be removed. xargs basename tries to run basename with as many arguments as possible at once, which fails; xargs -I{} basename {} causes xargs to run basename once per name to process.

Compare the outputs of

printf "foo\nbar\nbaz" | xargs echo basename


printf "foo\nbar\nbaz" | xargs -I{} echo basename {}

GNU basename supports a couple of options to allow multiple names; if you don’t need to specify a suffix:

xargs basename -a

and if you do,

xargs basename -s .suffix
  • 1
    In any case, it should rather be compgen -G "$glob" | xargs -rd '\n' basename -a -- here (with the GNUisms). Still doesn't work for filenames with newline characters, the whole bash completion framework is broken by design and can't cope with arbitrary file paths. Mar 21, 2022 at 15:27

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