Bash check is file with variable name inside loop exists - bash

Question

I would like to check if a file exists. Of course this is explained in many places. Now I am inside a loop like:
for ((l=0;l<5;l+=1));
do
if -a FILENAMEl #FILENAME contains l!!!!!!!!!
then "FILENAMEl exists"
else
do
.............
fi
done
Any ideas?
Thanks so much!!!

Answer 1

The main problem is that you are mixing the syntax of a variable name l with that of a file name. If you wish to use them together, to form part of a filename with a variable, you need a syntax break (caused by "$"), or use braces ({}).
If the file name has a variable in the middle, then braces work best. For example: "my_file_${l}_head.txt" would create files like my_file_1_head.txt, my_file_2_head.txt, etc.
Here is your original example corrected:
for ((l=0;l<5;l+=1))
do
if test -a FILENAME$l
then echo "FILENAME$l exists"
else echo "FILENAME$l doesn't exist"
fi
done
However, I wouldn't write code this way.
I only took your example and changed it as little as possible to show you the essential difference.
Here's another way to write it, using a more DRY (Don't Repeat Yourself) approach:
for l in {1..5}; do
file="filename$l"
if [[ -a "$file" ]]; then
echo "$file exists"
else
echo "$file does not exist"
fi
done
If you want more minimalism, here's yet another approach:
for l in {1..5}; do f="filename$l"
[[ -a "$f" ]] && echo "$f exists" || echo "$f does not exist"
done
Now, if you need to do something other than just print out the status, using function calls to make the extra work modular works well:
for l in {1..5} ; do f="$filename$l"
[[ -a "$f" ] && process_file $f || non_existant_file $f
done
Then, elsewhere, you should define both process_file and non_existant_file:
process_file() {
local file="$1"
# do whatever is needed for an existing file
}
non_existant_file() {
local file="$1"
# do whatever is needed for a non-existant file
}

Answer 2

Assume you're trying to find which files exist in the filename format file1.csv, file2.csv, etc...
for i in {1..5};
do f="file$i.csv";
if test -e $f;
then echo "$f exists";
else echo "$f does not exist";
fi
done
Perhaps what you need is simply a find
find . -name "file?.csv" -size +10k
You can restrict the file name to suffix 1..5 and do an action on the find result (check for find's -exec or more generally xargs as below).
find . -name "file[1-5].csv" -size +10c | xargs head -1