Awk/sed script to convert a file from camelCase to underscores

Question

I want to convert several files in a project from camelCase to underscore_case.

I would like to have a onliner that only needs the filename

Answer 1

This might be what you want:

$ cat tst.awk
{
    head = ""
    tail = $0
    while ( match(tail,/[[:upper:]]/) ) {
        tgt = substr(tail,RSTART,1)
        if ( substr(tail,RSTART-1,1) ~ /[[:lower:]]/ ) {
            tgt = "_" tolower(tgt)
        }
        head = head substr(tail,1,RSTART-1) tgt
        tail = substr(tail,RSTART+1)
    }
    print head tail
}

$ cat file
nowIs theWinterOfOur disContent
From ThePlay About RichardIII

$ awk -f tst.awk file
now_is the_winter_of_our dis_content
From The_play About Richard_iII

but without your sample input and expected output it's just a guess.