Looping through files with spaces in the names?

I wrote the following script to diff the outputs of two directores with all the same files in them as such:

#!/bin/bash

for file in `find . -name "*.csv"`  
do
     echo "file = $file";
     diff $file /some/other/path/$file;
     read char;
done

I know there are other ways to achieve this. Curiously though, this script fails when the files have spaces in them. How can I deal with this?

Example output of find:

./zQuery - abc - Do Not Prompt for Date.csv

ANSWER:-

Short answer (closest to your answer, but handles spaces)
OIFS="$IFS"
IFS=$'\n'
for file in `find . -type f -name "*.csv"`  
do
     echo "file = $file"
     diff "$file" "/some/other/path/$file"
     read line
done
IFS="$OIFS"

Better answer (also handles wildcards and newlines in file names)
find . -type f -name "*.csv" -print0 | while IFS= read -r -d '' file; do
    echo "file = $file"
    diff "$file" "/some/other/path/$file"
    read line </dev/tty
done

Best answer (based on Gilles' answer)
find . -type f -name '*.csv' -exec sh -c '
  file="$0"
  echo "$file"
  diff "$file" "/some/other/path/$file"
  read line </dev/tty
' {} ';'

Or even better, to avoid running one sh per file:
find . -type f -name '*.csv' -exec sh -c '
  for file do
    echo "$file"
    diff "$file" "/some/other/path/$file"
    read line </dev/tty
  done
' sh {} +


Long answer

You have three problems:

By default, the shell splits the output of a command on spaces, tabs, and newlines
Filenames could contain wildcard characters which would get expanded
What if there is a directory whose name ends in *.csv?


1. Splitting only on newlines

To figure out what to set file to, the shell has to take the output of find and interpret it somehow, otherwise file would just be the entire output of find.

The shell reads the IFS variable, which is which is set to <space><tab><newline> by default.

Then it looks at each character in the output of find. As soon as it sees any character that's inIFS, it thinks that marks the end of the file name, so it sets file to whatever characters it saw until now and runs the loop. Then it starts where it left off to get the next file name, and runs the next loop, etc., until it reaches the end of output.

So it's effectively doing this:
for file in "zquery" "-" "abc" ...

To tell it to only split the input on newlines, you need to do
IFS=$'\n'

before your for ... find command.

That sets IFS to a single newline, so it only splits on newlines, and not spaces and tabs as well.

If you are using sh or dash instead of ksh93, bash or zsh, you need to write IFS=$'\n' like this instead:
IFS='
'

That is probably enough to get your script working, but if you're interested to handle some other corner cases properly, read on...

2. Expanding $file without wildcards

Inside the loop where you do
diff $file /some/other/path/$file

the shell tries to expand $file (again!).

It could contain spaces, but since we already set IFS above, that won't be a problem here.

But it could also contain wildcard characters such as * or ?, which would lead to unpredictable behavior. (Thanks to Gilles for pointing this out.)

To tell the shell not to expand wildcard characters, put the variable inside double quotes, e.g.
diff "$file" "/some/other/path/$file"

The same problem could also bite us in
for file in `find . -name "*.csv"`

For example, if you had these three files
file1.csv
file2.csv
*.csv

(very unlikely, but still possible)

It would be as if you had run
for file in file1.csv file2.csv *.csv

which will get expanded to
for file in file1.csv file2.csv *.csv file1.csv file2.csv

causing file1.csv and file2.csv to be processed twice.

Instead, we have to do
find . -name "*.csv" -print | while IFS= read -r file; do
    echo "file = $file"
    diff "$file" "/some/other/path/$file"
    read line </dev/tty
done

read reads lines from standard input, splits the line into words according to IFS and stores them in the variable names that you specify.

Here, we're telling it not to split the line into words, and to store the line in $file.

Also note that read line has changed to read line </dev/tty.

This is because inside the loop, standard input is coming from find via the pipeline.

If we just did read, it would be consuming part or all of a file name, and some files would be skipped.

/dev/tty is the terminal where the user is running the script from. Note that this will cause an error if the script is run via cron, but I assume this is not important in this case.

Then, what if a file name contains newlines?

We can handle that by changing -print to -print0 and using read -d '' on the end of a pipeline:
find . -name "*.csv" -print0 | while IFS= read -r -d '' file; do
    echo "file = $file"
    diff "$file" "/some/other/path/$file"
    read char </dev/tty
done

This makes find put a null byte at the end of each file name. Null bytes are the only characters not allowed in file names, so this should handle all possible file names, no matter how weird.

To get the file name on the other side, we use IFS= read -r -d ''.

Where we used read above, we used the default line delimiter of newline, but now, find is using null as the line delimiter. In bash, you can't pass a NUL character in an argument to a command (even builtin ones), but bash understands -d '' as meaning NUL delimited. So we use -d '' to make read use the same line delimiter as find. Note that -d $'\0', incidentally, works as well, because bash not supporting NUL bytes treats it as the empty string.

To be correct, we also add -r, which says don't handle backslashes in file names specially. For example, without -r, \<newline> are removed, and \n is converted into n.

A more portable way of writing this that doesn't require bash or zsh or remembering all the above rules about null bytes (again, thanks to Gilles):
find . -name '*.csv' -exec sh -c '
  file="$0"
  echo "$file"
  diff "$file" "/some/other/path/$file"
  read char </dev/tty
' {} ';'

3. Skipping directories whose names end in *.csv
find . -name "*.csv"

will also match directories that are called something.csv.

To avoid this, add -type f to the find command.
find . -type f -name '*.csv' -exec sh -c '
  file="$0"
  echo "$file"
  diff "$file" "/some/other/path/$file"
  read line </dev/tty
' {} ';'

As glenn jackman points out, in both of these examples, the commands to execute for each file are being run in a subshell, so if you change any variables inside the loop, they will be forgotten.

If you need to set variables and have them still set at the end of the loop, you can rewrite it to use process substitution like this:
i=0
while IFS= read -r -d '' file; do
    echo "file = $file"
    diff "$file" "/some/other/path/$file"
    read line </dev/tty
    i=$((i+1))
done < <(find . -type f -name '*.csv' -print0)
echo "$i files processed"

Note that if you try copying and pasting this at the command line, read line will consume the echo "$i files processed", so that command won't get run.

To avoid this, you could remove read line </dev/tty and send the result to a pager like less.


NOTES

I removed the semi-colons (;) inside the loop. You can put them back if you want, but they are not needed.

These days, $(command) is more common than `command`. This is mainly because it's easier to write $(command1 $(command2)) than `command1 \`command2\``.

read char doesn't really read a character. It reads a whole line so I changed it to read line.