quel est le sens de cette commande sed: `; / @ / {h; s / test / next / g; x; G}`?

sed -e 's/72;/72, next_val = 0x11111111;/;/@/{h;s/test/next/g;x;G}'
fmt_vuln.c > fmt_vuln2.c

pourriez-vous me dire quel est le sens de ;/@/{h;s/test/next/g;x;G}?

;/@/{h;s/test/next/g;x;G}? 

/@/  search for an `@` sign
{}   for the lines where that is true do this 'block' of code
h    put the pattern match in the hold space
s/   substitute test for next everywhere in the space
g    do the previous substitution for all matches on the line
x    swap the hold with the pattern space
G    Add a new line with the contents of the hold space.

/@/ # For pattern-space containing the character @ do the following
{
  h              # place a copy of the pattern-space into the hold-space
  s/test/next/g  # replace all instances of "test" with "next" in the pattern-space
  x              # swap the pattern-space with the hold-space
  G              # append a newline followed by contents of hold-space to the pattern-space
}

Ainsi, pour chaque ligne contenant un @, la version modifiée de l'espace de motif sera imprimée suivie de l'original (l'espace de maintien contient la version non modifiée).

voir le résumé des commandes pour Sed