Shell Script : How use find expression in a for?

Question

I would like to use the find command in a for. So I did this:

for logs in `find $BACKUP_FOLDER -exec ls -la {} \; | awk '{ if ( $8==2011) printf $0"\n" }'`; do
// some command here
done;

But it seems to not be working, so if I try to find out how the command is being interpreated, I put this line alone in my script:

echo "$BACKUP_FOLDER -exec ls -la {} \; | awk { if ( '$8'==2011) printf $0"\n" }";

And the $8 appears blank and the \n is blank too. This is what is printed in terminal

/company-logs/engine -exec ls -la {} \; | awk { if ( ''==2011) printf /company/scripts/server/backup/sync_backup.shn }

How can I fix this ?

Answer 1

Your question

echo "$BACKUP_FOLDER -exec ls -la {} \; | awk { if ( '$8'==2011) printf $0"\n" }";

won't display anything useful for two reasons:

• In order to see the command as it would get executed by the shell, you have to escape the special characters $ and " with a backslash.

• $8 is just the eighth command-line argument for bash. To see what awk would replace it with, execute this command instead:

  find $BACKUP_FOLDER -exec ls -la {} \; | awk '{ if ( $8==2011) printf $0"\n" }'
  

Your approach

Your for loop doesn't work since printf $0 prints an entire line from ls -l (containing permissions, owners, date and time).

To fix this, you have to eliminate all but the bare file name using, e.g., awk itself or cut:

for logs in `find "$BACKUP_FOLDER" -exec ls -la {} \; | awk '{ if ( $8==2011) print $0 }' | cut -c 43-`; do ... done

This will create problems if there are spaces in the filenames. Setting the internal file separator to new-line only (IFS=$'\n' in bash) should take care of spaces.

Your problem

Your approach isn't very portable, since a different version of ls or a different locale might alter the fields.

To process all files from 2011, instead of your approach, I'd use

for logs in $(find "$BACKUP_FOLDER" -exec bash -c '[[ "$(stat -c %y "$0")" =~ ^2011 ]]' {} \; -print); do ... done

or, if possible,

find "$BACKUP_FOLDER" -exec bash -c '[[ "$(stat -c %y "$0")" =~ ^2011 ]]' {} \; -exec ... \;

Again, modifying the IFS should take care of spaces, but the second approach will be more reliable.

find replaces {} with the currently processed file and passes it as an argument to bash, which can access it as $0.

stat -c %y "$0" shows the modification time of $0 and [[ "$(...)" =~ ^2011 ]] checks if it begins with 2011.

If it does, bash -c '...' returns true and -print prints the filename or -exec executes a command.