command line find first file in a directory
If first means whatever the shell glob finds first (lexical, but probably affected by LC_COLLATE), then this should work:
for dir in */; do for file in "$dir"*.jpg; do echo mv "$file" "${file%/*}.jpg" # If it does what you want, remove the echo break 1 donedoneProof of concept:
$ mkdir dir{1,2,3} && touch dir{1,2,3}/file{1,2,3}.jpg$ for dir in */; do for file in "$dir"*.jpg; do echo mv "$file" "${file%/*}.jpg"; break 1; done; donemv dir1/file1.jpg dir1.jpgmv dir2/file1.jpg dir2.jpgmv dir3/file1.jpg dir3.jpg