Shell Programming and Scripting

$ ls
test1.txt  test2.txt  test3.txt  test4.txt  test5.txt  test_script.sh

#!/bin/bash

for  filename in /shell_expansion/*.txt; do
           for ((i=0; i<=3; i++)); do
               echo "$filename"
           done
done

./test_script.sh
/shell_expansion/*.txt
/shell_expansion/*.txt
/shell_expansion/*.txt
/shell_expansion/*.txt

for  filename in /shell_expansion/*.txt

for  filename in ./shell_expansion/*.txt

for  filename in shell_expansion/*.txt

#!/bin/bash
list_dir="." 
# list_dir is set to current pwd, 
# as you have shown your *txt files reside in the same pwd as your script...
# this actualy means, the 'cd $list_dir;' part would not be required, 
# but this would let you get the plain file names, rather than with the full path.
for filename in $(cd "$list_dir";ls *.txt | head -n4 )
do      echo "$filename"
done

$ ./test_script.sh
./shell_expansion/*.txt
./shell_expansion/*.txt
./shell_expansion/*.txt
./shell_expansion/*.txt


]$ ./test_script.sh
shell_expansion/*.txt
shell_expansion/*.txt
shell_expansion/*.txt
shell_expansion/*.txt

pwd
ls -l /shell_expansion/*.txt $HOME/shell_expansion/*.txt ./shell_expansion/*.txt ./*.txt