How to escape special characters in a string?

Question

Assuming $file holding a value of a file name, say Dr' A.tif. In bash programming, how could I escape single quote and any other special character of the $file without removing the special character?

Update on 9 July 2014

As request from @Gilles, following code snippet that doesn't able to handle Dr' A.tif:

files=$(find /path/ -maxdepth 1 -name "*.[Pp][Dd][Ff]" -o -name "*.[Tt][Ii][Ff]")
echo "${files}" > ${TEMP_FILE}
while read file
do
   newfile=$(echo "${file}" | sed 's, ,\\ ,g') ## line 1
done < ${TEMP_FILE}

After I have tried out the answer from @Patrick on line 1, it seems to work for me. But if I have file such as Dr\^s A.tif, printf command doesn't seem help, it shows me Dr\^s\ A.tif. If I manually try it on console like this:

printf "%q" "Dr\^s A.tif"

I will have this output:

Dr\\\^s\ A.tif

Any idea how to handle this?

Answer 1

You can use the printf builtin with %q to accomplish this. For example:

$ file="Dr' A.tif"
$ printf '%q\n' "$file"
Dr\'\ A.tif

$ file=' foo$bar\baz`'
$ printf '%q\n' "$file"
\ foo\$bar\\baz\`

From the bash documentation on printf:

In addition to the standard format specifications described in printf(1)
and printf(3), printf interprets:

 %b       expand backslash escape sequences in the corresponding argument
 %q       quote the argument in a way that can be reused as shell input
 %(fmt)T  output the date-time string resulting from using FMT as a format
          string for strftime(3)

Answer 2

Try:-

file=Dr\'\ A.tif
echo $file
Dr' A.tif

or

file="Dr' A.tif"
echo $file
Dr' A.tif

or if the string contains a double quote:-

file='Dr" A.tif'
echo $file
Dr" A.tif

There are good tutorials on escaping and quoting on the net. Start with this one.

Answer 3

You don't need to escape any file names you are handling in a script. Escaping is only necessary if you want to put a file name as a literal in a script, or to pass several file names as a single input stream to another script.

Since you're looping through the output of find, this is one of the simplest ways (!) to handle every possible path:

while IFS= read -r -d ''
do
    file_namex="$(basename -- "$REPLY"; echo x)"
    file_name="${file_namex%$'\nx'}"
    do_something -- "$file_name"
done <(find "$some_path" -exec printf '%s\0' {} +)

Answer 4

quick and (very) dirty

find . | sed 's/^/"/' | sed 's/$/"/'

Answer 5

A lot of these answers including the top-voted one using printf "%q" will not work in all cases without additional manipulation. I would suggest the following (example below):

cat <<EOF; 2015-11-07T03:34:41Z app[postgres.0000]: [TAG] text-search query doesn't contain lexemes: "" EOF