For loop using input file doesn't expand variables

Shell Programming and Scripting
1

Hi,

I'm using a for loop reading from an input file that contains files, whose path includes a variable name.

But the for loop doesn't expand the variable and therefore can't find the file.

Here's an example:

            File BACKUPFILES

/home/John/alpha
/home/Sue/beta
$BACKUP/listing/gamma

for i in `cat BACKUPFILES`
do
  file $i
done

           Output

/home/John/alpha:   ascii text

/home/Sue/beta:   ascii text
$BACKUP/listing/gamma:       cannot open: No such file or directory

The variable is set correctly - if I run echo $BACKUP in the for loop, it displays it correctly.

Does anyone know how to get around this? Thanks

2

could you mention where u set the variable value (BACKUP)???
use tag..( in tool bar use # symbol )

thanks

3

BACKUP is a variable set globally at login - it's not in /etc/profile, but all users process a login script that sets this and other variables.

4

try this:

for i in `cat BACKUPFILES`
do
  file $(eval echo $i)
done

another, more efficient approach may be:

while read i
do
 file $(eval echo $i)
done < BACKUPFILES
5

Great - both solution worked. Thanks for your help - but could you tell me why the second solution is more efficient than the first? I've got into the habit of using for loops.

6

Nothing but this avoids creating an extra process with calling an external command (cat).

"While read" the thing for these kind of purpose. ( reading file ).

7

OK - will remember that. Thanks for your help.

8

It also prevents problems should BACKUPFILES exceed the maximum size your shell allows for variables. This and related programming mistakes are described in more detail here.

1 Like
9

set BAKCUPFILES="/home/xyz/abc /home/xyz/prq"

use cat as mentoned above and check it.