When I tried to execute the following line at the command prompt, It is working properly..

grep flux file1.out > file1.csv

But when I supply this line in a 'other.txt' file, it is giving me the error :

No such file or directory

The file contents are :

grep flux file1.out > file1.csv
grep flux file2.out > file2.csv
grep flux file3.out > file3.csv
grep flux file4.out > file4.csv

Not clear to me.
What did you type at the command prompt which gave the error message "No such file or directory" ? Please post the full message because that usually contains the name of the file which cannot be found.
Please post which Operating System you have and which shell?

Which file?

Try specifying the directory that the file is located in. If you are executing this from a different directory then the one that the file is located in then you would get this message.

Is it possible you typed something like

. /.other.txt

. ./other.txt

Keep the script file and file*.out file in same directory or give the full path of file*.out in the script file.