81 lines
2.3 KiB
Markdown
81 lines
2.3 KiB
Markdown
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title = "Vim: Expressions in replacement text"
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date = "2020-06-14"
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author = "Ceda EI"
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tags = ["vim", "neovim", "replacements"]
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keywords = ["vim", "neovim", "replacements"]
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description = "Modifying the selection in a :s[ubstitute]// command"
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showFullContent = false
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+++
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Often times I find myself needing to modify the selection in a substitute command in a non-trivial way. From a recent example, I needed to convert the numbers in the `id` of the `div`s to hexadecimal after decrementing them by 1.
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Basically, I had to convert
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```html
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<div id="someprefix1">
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...
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</div>
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<div id="someprefix2">
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...
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</div>
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<div id="someprefix3">
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...
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</div>
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<div id="someprefix4">
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...
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</div>
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...
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<div id="someprefix80">
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...
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</div>
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```
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to
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```html
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<div id="someprefix0">
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...
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</div>
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<div id="someprefix1">
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...
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</div>
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<div id="someprefix2">
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...
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</div>
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<div id="someprefix3">
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...
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</div>
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...
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<div id="someprefix4F">
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...
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</div>
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```
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Doing this manually is tiring, I could have used macros but I instead chose an even simpler approach.
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Vim allows to use expressions in the replacement part of the substitute command if it starts with `\=`. So, the replacement can be simply done using `\=` and `printf`. What I did was simply use the following command after selecting the text in a visual selection.
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`:'<,'>s/\v(someprefix)(\d+)/\=printf("%s%X", submatch(1), submatch(2) - 1)`
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The breakdown is as follows:
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- `:'<,'>`: Sets the range to visual selection.
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- `s/`: Starts the substitution.
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- `\v`: Enables "very magic mode". This allows for writing simpler regular expressions without having to escape special characters.
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- `(someprefix)(\d+)`: Captures the string `someprefix` in group 1 and the number that follows in group 2.
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- `/`: Ends the search and starts replacement.
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- `\=`: Tells Vim to treat the following text as an expression.
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- `printf(`: `printf` is a function that takes a format string and values for the format parameters.
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- `"%s%X"`: The format string. `%s` means to print the parameter as a string. `%X` means to convert the parameter to a hexadecimal number in capital letters (`%x` for small).
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- `submatch(1)`: It retrieves the first matched group.
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- `submatch(2) - 1`: It retrieves the second matched group and subtracts one from it.
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### References
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- `:help sub-replace-expression`
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- `:help submatch`
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- `:help printf`
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- `:help /magic`
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- `:help :s`
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