insert text five lines before each pattern match

Question

I have a file in which a pattern (eg: RotX) is repeated many times in a similar context. I need to insert a specific text (eg: Rot-X) at the start of every line which is located five lines before every pattern match:

...

_face_641
{
    type wall;
    nFaces 6;
    startFace 63948413;
    inGroups       1(RotX);
}

_face_821
{
    type wall;
    nFaces 3;
    startFace 63948419;
    inGroups       1(RotX);
}

_face_67
{
    type wall;
    nFaces 3;
    startFace 63948422;
    inGroups       1(RotX);
}

...

should become

...

Rot-X_face_641
{
    type wall;
    nFaces 6;
    startFace 63948413;
    inGroups       1(RotX);
}

Rot-X_face_821
{
    type wall;
    nFaces 3;
    startFace 63948419;
    inGroups       1(RotX);
}

Rot-X_face_67
{
    type wall;
    nFaces 3;
    startFace 63948422;
    inGroups       1(RotX);
}

...        

Could this be done using sed or awk ?

Many thanks in advance for your help

Answer 1

Using a simple 2-pass approach:

$ awk 'NR==FNR{ if (/RotX/) nrs[NR-5]; next } FNR in nrs{ $0="Rot-X" $0 } 1' file file
...

Rot-X_face_641
{
    type wall;
    nFaces 6;
    startFace 63948413;
    inGroups       1(RotX);
}

Rot-X_face_821
{
    type wall;
    nFaces 3;
    startFace 63948419;
    inGroups       1(RotX);
}

Rot-X_face_67
{
    type wall;
    nFaces 3;
    startFace 63948422;
    inGroups       1(RotX);
}

...

Answer 2

Using vim

vim -c "g/RotX/norm 5kIRot-x" -c "wq" file.txt

Using ed: From @steeldriver

printf '%s\n' 'g/(RotX)/-5s/^/Rot-X/' 'wq' | ed -s file.txt

---

If the braces {, need not be exactly 4 lines above but otherwise same format,

vim -c "g/RotX/norm [{kIRot-X" -c "wq" file.txt
printf "%s\n" 'g/RotX/?^{$?-1s/^/Rot-X/' 'wq' | ed -s file.txt

Answer 3

A single pass with awk:

# insert_before_match.awk
{
    p6=p5
    p5=p4
    p4=p3
    p3=p2
    p2=p1
    p1=$0

    if ($0 ~ /RotX/) {
        print "Rot-X"p6
        print p5
        print p4
        print p3
        print p2
        print p1
        print "}"
        print ""
    }

}

$ awk -f insert_before_match.awk infile

Rot-X_face_641
{
    type wall;
    nFaces 6;
    startFace 63948413;
    inGroups       1(RotX);
}

Rot-X_face_821
{
    type wall;
    nFaces 3;
    startFace 63948419;
    inGroups       1(RotX);
}

Rot-X_face_67
{
    type wall;
    nFaces 3;
    startFace 63948422;
    inGroups       1(RotX);
}