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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?

Community
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huahsin68
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    in what context are you expecting to use $file? or is this issue assigning the string with the special character to $file? – rob Jul 08 '14 at 10:50
  • Actually the find command return me an array of file list. And then I loop through this file list into $file variable. – huahsin68 Jul 08 '14 at 10:56
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    You've been given some correct answers here, but they are probably not the answers to the question that you're really asking. From your comment here, I strongly suspect that you're on the wrong track. We can't help you much because you keep not showing your code. I do however recommend that you read [Why does my shell script choke on whitespace or other special characters?](http://unix.stackexchange.com/questions/131766/why-does-my-shell-script-choke-on-whitespace-or-other-special-characters) as background. **Show your script and explain what you want to do.** – Gilles 'SO- stop being evil' Jul 08 '14 at 21:18

5 Answers5

25

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)
wjandrea
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phemmer
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    This doesn't work with certain cases .e.g. when you need to preserve double-quotes. – user3467349 Nov 07 '15 at 06:08
  • @user3467349 it works just fine with quotes. I'm betting you're trying something like `printf '%s' "foo"`. You need to understand how argument parsing works in the shell first. See https://www.gnu.org/software/bash/manual/bash.html#Shell-Operation #2 happens before #6. – phemmer Nov 07 '15 at 18:49
  • Could you provide an example of this string printed with `printf` and no other manipulations `It doesn't have a: ""` – user3467349 Nov 08 '15 at 04:25
  • Your issue has nothing to do with `printf`. Your issue is that you don't want the shell to parse your string. In order to do that, you have to pass your input to the shell in a way where it doesn't even try to parse it. One way to do this would be `read -r -p 'input: ' && printf '%q\n' "$REPLY"`, and provide the input when prompted. – phemmer Nov 08 '15 at 06:48
  • Provide input while prompted won't work well in a shell script, neither is it speedy even interactively. Hence my above comment about this being a limited / sub-optimal solution. – user3467349 Nov 08 '15 at 10:10
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    As i've said several times now. Not knowing how how to pass raw data to the shell isn't an issue with `printf`. Perhaps you should ask a question rather than critiquing a solution that has nothing to do with your problem. – phemmer Nov 08 '15 at 15:16
  • You can use `cat < – user3467349 Nov 08 '15 at 15:38
  • For a more modern version of this answer without `printf`, see https://stackoverflow.com/a/27817504/442022 . – colan Aug 23 '21 at 17:53
4

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.

garethTheRed
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1

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' {} +)
l0b0
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0

quick and (very) dirty

find . | sed 's/^/"/' | sed 's/$/"/'
chaos
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Michael
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-1

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

user3467349
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  • Excuse the n00b question but can you elaborate on how you would actually use this to escape characters in a string? If I copy the code you write into my terminal it just prints 2015-11-07T03:34:41Z app[postgres.0000]: [TAG] text-search query doesn't contain lexemes: "" ...nothing is escaped. – SharkAlley Sep 08 '16 at 05:45
  • That's literally the point, all of the special characters *are* interpreted as literal characters not for their special meaning. Try to *echo* "the above string" instead to see the difference. – user3467349 Sep 12 '16 at 14:11