Question

I have a very large input set that looks something like this:

Label: foo, Other text: text description...
   <insert label> Item: item description...
   <insert label> Item: item description...
Label: bar, Other text:...
   <insert label> Item:...
Label: baz, Other text:...
   <insert label> Item:...
   <insert label> Item:...
   <insert label> Item:...
...

I’d like to transform this to pull out the label name (e.g. "foo") and replace the tag "<insert label>" on the following lines with the actual label.

Label: foo, Other text: text description...
   foo Item: item description...
   foo Item: item description...
Label: bar, Other text:...
   bar Item:...
Label: baz, Other text:...
   baz Item:...
   baz Item:...
   baz Item:...
...

Can this be done with sed or awk or other unix tool? If so, how might I do it?

Answer 1

One solution using sed:

Content of script.sed:

## When line beginning with the 'label' string.
/^Label/ {
    ## Save content to 'hold space'.
    h   

    ## Get the string after the label (removing all other characters)
    s/^[^ ]*\([^,]*\).*$/\1/

    ## Save it in 'hold space' and get the original content
    ## of the line (exchange contents).
    x   

    ## Print and read next line.
    b   
}
###--- Commented this wrong behaviour ---###    
#--- G
#--- s/<[^>]*>\(.*\)\n\(.*\)$/\2\1/

###--- And fixed with this ---###
## When line begins with '<insert label>'
/<insert label>/ {
    ## Append the label name to the line.
    G   

    ## And substitute the '<insert label>' string with it.
    s/<insert label>\(.*\)\n\(.*\)$/\2\1/
}

Content of infile:

Label: foo, Other text: text description...
   <insert label> Item: item description...
   <insert label> Item: item description...
Label: bar, Other text:...
   <insert label> Item:...
Label: baz, Other text:...
   <insert label> Item:...
   <insert label> Item:...
   <insert label> Item:...

Run it like:

sed -f script.sed infile

And result:

Label: foo, Other text: text description...
    foo Item: item description...
    foo Item: item description...
Label: bar, Other text:...
    bar Item:...
Label: baz, Other text:...
    baz Item:...
    baz Item:...
    baz Item:...