Suppose you want to change the following
| original | new | |
|---|---|---|
| a \ttimes b | -> |
= |
| a \\ttimes b | -> |
= |
| a_2 |
-> |
a_2 \btimes b |
| a_2 |
-> |
a_2 \\btimes b |
| a_{2} |
-> |
a_{2} \btimes b |
| a_{2} |
-> |
a_{2} \\btimes b |
| a_{V[i]} |
-> |
a_{V[i]} \btimes b |
| a_{V[i]} |
-> |
a_{V[i]} \\btimes b |
Finding the cases that need substitution is easy
ag "_\\{?([A-Za-z0-9-]*)?(\\[(?1)\\])?\\}? *\\\?\\\ttimes"
But this will select everything starting from the underscore
- a _2 \ttimes b
- a _2 \\ttimes b
- a _{2} \ttimes b
- a _{2} \\ttimes b
- a _{V[i]} \ttimes b
- a _{V[i]} \\ttimes b
but really you only want to select only ttimes
- a_2 \ttimes b
- a_2 \ttimes b
- a_{2} \ttimes b
- a_{2} \ttimes b
- a_{V[i]} \ttimes b
- a_{V[i]} \ttimes b
Lookbehind would the solution, so really you only need to enclose the part in the regex preceding ttimes within (?<=...), i.e.
ag "(?<=_\\{?([A-Za-z0-9-]*)?(\\[(?1)\\])?\\}? *\\\?\\\)ttimes"
sadly, ack/ag don't support variable length expressions within the lookbehind expression, so you would get the following error:
ERR: pcre_compile failed at position 42. Error: lookbehind assertion is not fixed length