Add, move commands in shell syntax file

[niten94]

The commands below are added in this pull request:

• break
• command
• continue
• eval
• exec - There are times the command is used with replacing the shell process and other commands in a script are not run when it is replaced, so it is added in the "Conditionals and control flow" group.
• getopt
• getopts
• trap - It is usually used with running a command when a signal is received so it is added in the "Conditionals and control flow" group.
• wait - The command returns when commands in background have finished running so it is added in the "Conditionals and control flow" group.

The commands below are highlighted using a different color group in this pull request:

• local
• read
• shift
• time

The commands that are added and moved except getopt are usually builtin commands in sh implementations so they can be looked up in reference pages of those implementations.

[dmaluka]

Strictly speaking, eval, exec, getopts and trap are builtins, not keywords, so perhaps it's better to move them to the "Shell commands" group below? (The same actually applies to exit, read, shift and time.)

I'm actually not against highlighting them as keywords, if that's more practical. But then it's not clear why e.g. exec and exit are highlighted as keywords but e.g. export and set are not.

[niten94]

I wrote that most of the commands added are builtin commands so that it would be known where the commands can be looked up when using something like man.

I do not know why time would be highlighted as a keyword but I was thinking that commands like exec and exit would be highlighted as such because they are used with control flow.

I think read and shift are also highlighted as keywords because they are sometimes used in loops. I realized that I have not seen eval being used with control flow so I am thinking about moving it to "Shell commands".

I do not mind much about how commands and keywords are highlighted so I do not know if moving builtin commands to "Shell commands" would be better, but I still do not think people would mind that much.

[dmaluka]

I think now I understand what should be the criteria: "Conditionals and control flow" should include those commands that actually affect control flow, not just are often used in loops. I.e. break, continue, return - as I've realized, technically these are not keywords (i.e. not special syntax constructs), but they affect the control flow, i.e. they determine which command will be executed next, so they should be highlighted as "Conditionals and control flow" together with keywords.

See for example the Flow-Control Constructs section in https://linux.die.net/man/1/dash.

exec, exit - arguably these also can be considered as control-flow commands, as they affect execution of the entire script.

But getopts, read, shift, time and trap - these should be moved to "Shell commands", it seems.

[dmaluka]

Well, trap might be an exception: it does affect the execution flow of the script (although not immediately), so we may leave it in "Conditionals and control flow".

[dmaluka]

Also I'm not quite sure what to do with local, which is also technically a command, not a keyword.

local, let, set, export and read are all related to setting shell variables, so it might make sense to highlight them all the same way.

[niten94]

I think local was in "Conditionals and control flow" because the value of specified variables where the function is run is not modified.

I think it would be better moving getopts, local, read, shift and time to "Shell commands" because control flow is not affected when they are run, but I will move them in this pull request.

Edit: I have also added wait.

[niten94]

eval was highlighted as a keyword because commands like exit can be run using it, but such commands are not usually run using eval so I have moved it to "Shell commands". I was also thinking about the same with command so the note about command in the pull request description has been removed.

The pull request description has also been edited so that it would be a bit more clear why some commands were added in "Conditionals and control flow".

[dmaluka]

LGTM. @JoeKar WDYT?