How to make a loop for getting input and output - bash

Question

I have a command line like this:
myscript constant/tap.txt -n base.dat -c normal/sta0.grs -o normal/brs0.opm
I have 100 .grs files and I need to generate 100 .opm files.
I want to put the command above into a loop that does the following:
myscript constant/tap.txt -n base.dat -c normal/sta0.grs -o normal/brs0.opm
myscript constant/tap.txt -n base.dat -c normal/sta1.grs -o normal/brs1.opm
myscript constant/tap.txt -n base.dat -c normal/sta2.grs -o normal/brs2.opm
myscript constant/tap.txt -n base.dat -c normal/sta3.grs -o normal/brs3.opm
myscript constant/tap.txt -n base.dat -c normal/sta4.grs -o normal/brs4.opm
.
.
.
myscript constant/tap.txt -n base.dat -c normal/sta100.grs -o normal/brs100.opm
I was trying to make it like below:
#!/bin/bash
# Basic until loop
counter=100
until [ $counter -gt 100 ]
do
myscript constant/tap.txt -n base.dat -c normal/sta100.grs -o normal/brs100.opm
done
echo All done
but I could not find a way to set the parameters changes during the loop
In the above command these are constant for each run:
myscript constant/tap.txt -n base.dat -c
The only thing that changes in each loop is the following input and output:
normal/sta100.grs
normal/brs100.opm
I have 100 of sta.grs in the normal folder and I want to create 100 of brs.opm in the normal folder.

Answer 1

#!/bin/bash
counter=0
until ((counter>100))
do
myscript constant/tap.txt -n base.dat -c normal/sta$counter.grs -o normal/brs$counter.opm
((++counter))
done
echo 'All done'

Answer 2

This is an excellent use case for GNU parallel:
find normal -name '*.grs' |
parallel myscript constant/tap.txt -n base.dat -c {} -o {.}.opm
The less code you write, the less errors you make. And this generalizes nicely to cases where your files are named in more complex patterns. And you get parallelization for free (you can get rid of it with -j1).

Answer 3

Instead of incrementing the counter manually, you could use a for loop like this:
for i in {0..100}; do
myscript constant/tap.txt -n base.dat -c normal/sta"$i".grs -o normal/"$i".opm
done
Also, consider that this will sort in an unintuitive way:
1.opm
10.opm
100.opm
11.opm
12.opm
so maybe use padded numbers everywhere with for i in {000..100}; do. This requires Bash 4.0 or newer; if you don't have that, you could do something like
for i in {0..100}; do
printf -v ipad '%03d' "$i"
myscript constant/tap.txt -n base.dat -c normal/sta"$ipad".grs \
-o normal/"$ipad".opm
done
where the printf line puts a padded version of the counter into the ipad variable.
(And if you have Bash older than 3.1, you can't use printf -v and have to do
ipad=$(printf '%03d' "$i")
instead.)