BASH: FOR control with two variables?

fopetesl · 12-07-2007, 12:41 PM

I'm trying to write a script which loops copying dual files to another directory but (even having RTFM) I can't find a way to do it.
There doesn't seem to be an AND control I can use.

Code:

for file in *.dta
do
cp -f $file /home/mystuff/datafile.dta
done

works fine for every single file in the current directory.

However what I actually need to do is something like this

Code:

for fileA in *F.dta AND fileB in *R.dta
do
cp -f $fileA /home/mystuff/datafileF.dta
cp -f $fileB /home/mystuff/datafileR.dta
done

Doesn't throw any warnings except the $fileB copy fails with "can't find directory"

In C it would be a piece of cake so there must be a way in BASH. No?

matthewg42 · 12-07-2007, 01:03 PM

Can you guarantee that for every *F.dta there is a corresponding *R.dat?

If so, you can iterate over the list of all *F.dta, but for each iteration perform a second copy operation replacing the F.dat ending with R.dat. In this example I check to see if there is a corresponding file, and do the copy of both only if this is true:

Code:

for f_file in *F.dta; do
    d_file="${f_file%F.dta}D.dta"
    if [ -a "$d_file" ]; then
        echo "replace this with some copy operation which you like"
    else
        echo "there is no file $d_file corresponding to $f_file"
    fi
done

rupertwh · 12-07-2007, 01:21 PM

Quote:

Originally Posted by fopetesl

Code:

for fileA in *F.dta AND fileB in *R.dta
do
cp -f $fileA /home/mystuff/datafileF.dta
cp -f $fileB /home/mystuff/datafileR.dta
done

Doesn't throw any warnings except the $fileB copy fails with "can't find directory"

That, of course doesn't work. (What it does is assign to fileA in sequence: All matches for *F.dta, then 'AND', then 'fileB', then all matches for *R.dta. fileB never becomes a variable)

I'm not sure, though what you actually intended to do. Is it

Copy all *F.dta files and all *R.dta?
Code:
```
for file in *F.dta *R.dta ; do ...
```
would do that.
But so would a simple
Code:
```
cp *F.dta *R.dta /home/mystuff
```
Only if there are corresponding *F.dta and *R.dta then copy both of them?
Just iterate over one of them, then inside the loop check if the corresponding file exists, then copy both:
Code:
```
for fileA in *F.dta ; do
        fileB="${fileA%F.dta}R.dta"
        if [ -f "$fileB" ] ; then
                cp ...
```
PS: Which is basically what Matthew already wrote. Didn't see that at first. (But you don't need to guarantee they both exist, as you're checking for that inside the loop)

fopetesl · 12-08-2007, 03:07 AM

Maybe I have an answer here. However, to clarify:
I should have made it clearer that files named *F.dta need to be copied to a specific filename, always the same.
So a file originally named, say, "20071208134214F.dta" (note the date and time) would have to be copied to "AlwaysUseSameFileName_F.dta".
Similarly for the 'R' file.
There are always matched pairs of *.dta files.

I have a C program which processes the data from the two resultant files, "AlwaysUseSameFileName_F.dta" and "AlwaysUseSameFileName_R.dta"

So My original (incorrect) code should have read:

Code:

for fileA in *F.dta AND fileB in *R.dta
do
cp -f $fileA /home/mystuff/AlwaysUseSameFileNameF.dta
cp -f $fileB /home/mystuff/AlwaysUseSameFileNameR.dta
cd /home/mystuff
./ProcessTheTwoSiblingDataFiles
cd /home/logfiles
# go round this loop until all pairs of *.dta files are processed
done

Thanks, guys. Will check out your idea(s) later (have vehicle problems,

sigh).

Thanks, Matthew. Thanks, Rupert. Works just great.
What I don't understand is why it works.
For instance

Code:

d_file="${f_file%F.dta}D.dta"
    if [ -a "$d_file" ]; then

has me totally bemused.
I can't see how the parameter from $f_file is taken and converted into D.dta and hence into $d_file. Is it an increment on $f_file to find D.dta?
Whatever, it works