Why does a file move/copy function only move one file at a time when using the “*” wildcard?

Question

function mv1 { mv -n "$1" "targetdir" -v |wc -l ;}
mv1 *.png

It does only move the first .png file it finds, not all of them.

How can I make the command apply to all files that match the wildcards?

Answer 1

mv1 *.png first expands the wildcard pattern *.png into the list of matching file names, then passes that list of file names to the function.

Then, inside the function $1 means: take the first argument to the function, split it where it contains whitespace, and replace any of the whitespace-separated parts that contain wildcard characters and match at least one file name by the list of matching file names. Sounds complicated? It is, and this behavior is only occasionally useful and is often problematic. This splitting and matching behavior only occurs if $1 occurs outside of double quotes, so the fix is easy: use double quotes. Always put double quotes around variable substitutions unless you have a good reason not to.

For example, if the current directory contains the two files A* algorithm.png and graph1.png, then mv1 *.png passes A* algorithm.png as the first argument to the function and graph1.png as the second argument. Then $1 is split into A* and algorithm.png. The pattern A* matches A* algorithm.png, and algorithm.png doesn't contain wildcard characters. So the function ends up running mv with the arguments -n, A* algorithm.png, algorithm.png, targetdir and -v. If you correct the function to

function mv1 { mv -n "$1" "targetdir" -v |wc -l ;}

then it will correctly move the first file.

To process all the arguments, tell the shell to process all arguments and not just the first. You can use "$@" to mean the full list of arguments passed to the function.

function mv1 { mv -n "$@" "targetdir" -v |wc -l ;}

This is almost correct, but it still fails if a file name happens to begin with the character -, because mv will treat that argument as an option. Pass -- to mv to tell it “no more options after this point”. This is a very common convention that most commands support.

function mv1 { mv -n -v -- "$@" "targetdir" |wc -l ;}

A remaining problem is that if mv fails, this function returns a success status, because the exit status of commands on the left-hand side of a pipe is ignored. In bash (or ksh), you can use set -o pipefail to make the pipeline fail. Note that setting this option may cause other code running in the same shell to fail, so you should set it locally in the function, which is possible since bash 4.4.

function mv1 {
  local -
  set -o pipefail
  mv -n -v -- "$@" "targetdir" | wc -l
}

In earlier versions, setting pipefail would be fragile, so it would be better to check PIPESTATUS explicitly instead.

function mv1 {
  mv -n -v -- "$@" "targetdir" | wc -l
  ((!${PIPESTATUS[0] && !${PIPESTATUS[1]}}))
}

Answer 2

$1 is the first argument to the function, here the first file that matches *.png. I guess that "$@" is what you want to use instead of $1.

Answer 3

You would have to use mv1 \*.png.

When interacting with functions, the Linux Terminal does not pass the asterisk directly to the command, but selects the first matching parameter and passes that one to the command.

To allow the asterisk to pass through directly, one needs to escape the asterisk using a backslash.