[SOLVED] weird behaviour of redirection in command substitution in find -exec

doru · 07-29-2022, 11:14 AM

Please explain the effect of redirection on this command:

Code:

~/tmp/find$ touch file file1
~/tmp/find$ find . -name f\* -exec bash -c "echo $(ls {})" \;     
ls: cannot access '{}': No such file or directory


~/tmp/find$ find . -name f\* -exec bash -c "echo $(ls {} 2>&1)" \;
ls: cannot access ./file1: No such file or directory
ls: cannot access ./file: No such file or directory

In the first case, $(ls {}) is substituted before find is called, which is normal.
But in the second case, for some reason, {} is substituted with file names and then ls can not find the already found files!

doru · 07-29-2022, 05:33 PM

In the first case, bash substitutes $(ls {}) on the command line with nothing, and the "ls: cannot access '{}': No such file or directory" message is printed through the stderr.

In the second case, bash substitutes $(ls {}) with "ls: cannot access '{}': No such file or directory", and then find substitutes '{}' with found files and echo prints the resulting message. ls is never invoked for a second time.

NevemTeve · 07-30-2022, 06:38 AM

Code:

find . -name f\* -exec bash -c "echo $(ls {})" \;

first prints this:

Code:

ls: cannot access '{}': No such file or directory

then executes this:

Code:

find . -name f\* -exec bash -c "echo ''" \;

Code:

~/tmp/find$ find . -name f\* -exec bash -c "echo $(ls {} 2>&1)" \;

executes this:

Code:

~/tmp/find$ find . -name f\* -exec bash -c "echo ls: cannot access '{}': No such file or directory" \;