Escaping both forward slash and back slash with sed

I have the following string: /tmp/test/folder1/test.txt

I wish to use sed to substitute / for / – for example:

/tmp/test/folder1/test.txt

So I issue:

echo "/tmp/test/folder1/test.txt" | sed "s///\\//g"

Although it returns:

sed: -e expression #1, char 9: unknown option to `s’

I am escaping the forward slash and backslash – so not sure where I have gone wrong here

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Answers:

Method 1

Method 2

Method 3

Answers:

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Method 1

You need to escape (with backslash ) all substituted slashes / and all backslashes separately, so:

$ echo "/tmp/test/folder1/test.txt" | sed 's///\//g'
/tmp/test/folder1/test.txt

but that’s rather unreadable.

However, sed allows to use almost any character as a separator instead of /, this is especially useful when one wants to substitute slash / itself, as in your case, so using for example semicolon ; as separator the command would become simpler:

echo "/tmp/test/folder1/test.txt" | sed 's;/;\/;g'

Other cases:

If one wants to stick with slash as a separator and use double quotes then all escaped backslashes have to be escaped one more time to preserve their literal values:
```
echo "/tmp/test/folder1/test.txt" | sed "s///\\//g"
```
if one doesn’t want quotes at all then yet another backslash is needed:
```
echo "/tmp/test/folder1/test.txt" | sed s/\//\\\//g
```

Method 2

Or, if the value is in a (bash) shell variable:

var=/tmp/test/folder1/test.txt
$ echo "${var////\/}"
/tmp/test/folder1/test.txt

The first // start parameter expansion, saying to replace all matches with the replacement. The next / is the escaped / to match, and the \/ is an escaped followed by an escaped / as the replacement.

Method 3

The final solution will be this one:

$ sed 's:/:\/:g'  <<<"$str"
/tmp/test/folder1/test.txt

But to explain how to get there:
Yes, you were missing one backslash:

$ str='/tmp/test/folder1/test.txt'
$ sed "s///\\//g" <<<"$str"
/tmp/test/folder1/test.txt

I hope that one space will make it clear:

$ sed "s///\\ //g"  <<<"$str"
 /tmp /test /folder1 /test.txt

But, if you were to change the sed delimiter to : (for example):

$  sed "s:/:\\/:g"  <<<"$str"
/tmp/test/folder1/test.txt

But that is not strictly correct as the (now not special) / does not need scaping:

$ sed "s:/:\\/:g"  <<<"$str"
/tmp/test/folder1/test.txt

And, if you were to use single quotes instead of double quotes the shell will not change double \ to one, so less will be correct:

$ sed 's:/:\/:g'  <<<"$str"
/tmp/test/folder1/test.txt

Which is quite cleaner.

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0

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