Bash Shell’s Tab Completion can be programmed and used to provide TAB completion for any cli program that you write, given that the your program is able to read in environment variables.
Bash has the complete builtin that can be used to specify how TAB completion
must be performed when invoking a particular command. There are multiple ways
a so called compspec (Completion Specification) can be specified using the
complete builtin, but the most flexible in my opinion is by using the -C
flag.
complete -C command name
name is the name of the program the completion specification is for.command is the name of a function or program that will provide the
completion output.When TAB is pressed while entering the arguments to name, the partially typed
arguments are put in and environment variable called COMP_LINE, along with
several other completion related variables:
COMP_CWORD: An index into ${COMP_WORDS} of the word containing the current
cursor position.
COMP_KEY: The key (or final key of a key sequence) used to invoke the current
completion function.
COMP_LINE: The current command line.
COMP_POINT: The index of the current cursor position relative to the beginning
of the current command. If the current cursor position is at the end of
the current command, the value of this variable is equal to ${#COMP_LINE}.
COMP_WORDBREAKS: The set of characters that the readline library treats as
word separators when performing word completion. If COMP_WORDBREAKS is
unset, it loses its special properties, even if it is subsequently reset.
COMP_WORDS: An array variable (see Arrays below) consisting of the individual
words in the current command line. The line is split into words as readline
would split it, using COMP_WORDBREAKS as described above.
From man bash:
… any shell function or command specified with the -F and -C options is invoked. When the command or function is invoked, the COMP_LINE, COMP_POINT, COMP_KEY, and COMP_TYPE variables are assigned values as described above under Shell Variables. If a shell function is being invoked, the COMP_WORDS and COMP_CWORD variables are also set. When the function or command is invoked, the first argument ($1) is the name of the command whose arguments are being completed, the second argument ($2) is the word being completed, and the third argument ($3) is the word preceding the word being completed on the current command line. No filtering of the generated completions against the word being completed is performed; the function or command has complete freedom in generating the matches.
The command can read these environment variables to output a list of newline
delimited completion candidates to stdout.
Related:
References:
man bashhelp completeTags:
#literature-note #scripting #programming