How to split long sed expression into multiple lines?

Question

sed 's/[long1][long2]/[long3][long4]/' file.txt

I would like to split this command onto multiple lines - f.x. something like this:

sed 's/
    [long1]
    [long2]
  /
    [long3]
    [long4]
  /' file.txt

Using \ or separating strings didn't work.

Answer 1

sed 's'/\
'[long1]'\
'[long2]'\
'/'\
'[long3]'\
'[long4]'\
'/' file.txt

Splitting on several lines with backslash does work if new lines are not indented.

$ echo "a,b" | sed 's/\(.'\
> '\),\(.\)/\2-\1/'
b-a

Tested on Cygwin with GNU sed 4.2.2

Answer 2

Another aspect:

How maintainable are the [long] items above?

The shorter and more distinct you can keep the clauses, the easier they will be to change and enhance as time passes and (sed-external) facts change around the the function they provide.

e.g.

sed \
-e 's/[minimal-s1]/[minimal-r1]/' \
-e 's/[minimal-s2]/[minimal-r2]/' \
-e 's/[minimal-s3]/[minimal-r3]/' \
-e 's/[minimal-s4]/[minimal-r4]/' 

... might be something to strive for and prefer.

Answer 3

You can save long string to bash variables, then use in sed command:

string=[long1][long2]
replace=[long3][long4]
sed -e 's/'"$string"'/'"$replace"'/' file

If you can use perl, you can break long pattern with x modifier:

perl -e 's/
[long1]
[long2]
/[long3][long4]/x' file

Answer 4

You can also break that up this way:

sed '/[long1][long2]/
    s//[long3][long4]/'

Or maybe like:

sed "$(
    printf 's/[%s][%s]/[%s][%s]/' \
        long1 \
        long2 \
        long3 \
        long4
)"

Or with a heredoc:

sed -f - <<SED file.txt
s/\
[long1]\
[long2]\
/\
[long3]\
[long4]\
/
SED