sed Substitution Pattern flags - occurrence replacement
Example
If we want to replace only the first occurrence in a line, we use sed as usual:
$ cat example
aaaaabbbbb
aaaaaccccc
aaaaaddddd
$ sed 's/a/x/' example
xaaaabbbbb
xaaaaccccc
xaaaaddddd
But what if we want to replace all occurrences?
We just add the g pattern flag at the end:
$ sed 's/a/x/g' example
xxxxxbbbbb
xxxxxccccc
xxxxxddddd
And if we want to replace one specific occurrence, we can actually specify which one:
$ sed 's/a/x/3' example
aaxaabbbbb
aaxaaccccc
aaxaaddddd
/3 being the 3rd occurrence.
GNU sed
From info sed, see GNU sed manual for online version
the POSIX standard does not specify what should happen when you mix the
gand NUMBER modifiers, and currently there is no widely agreed upon meaning acrosssedimplementations. For GNUsed, the interaction is defined to be: ignore matches before the NUMBERth, and then match and replace all matches from the NUMBERth on.
$ sed 's/b/y/2g' example
aaaaabyyyy
aaaaaccccc
aaaaaddddd
$ sed 's/c/z/g3' example
aaaaabbbbb
aaaaacczzz
aaaaaddddd
