abbr.fish: add abbr, a command to manipulate abbreviations

Work on #731.

doc_src/abbr.txt

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+\section abbr abbr - manage fish abbreviations
+
+\subsection abbr-synopsis Synopsis
+\fish{synopsis}
+abbr -a word="phrase"
+abbr -s
+abbr -l
+abbr -r word
+\endfish
+
+\subsection abbr-description Description
+
+`abbr` manipulates the list of abbreviations that fish will expand.
+
+Abbreviations are user-defined character sequences or words that are replaced with longer phrases after tehy are entered. For example, a frequently-run command such as `git checkout` can be abbreviated to `gco`. After entering `gco` and pressing @key{Space} or @key{Enter}, the full text `git checkout` will appear in the command line.
+
+Abbreviations are stored, by default, in a universal variable.
+
+The following parameters are available:
+
+- `-a 'WORD=PHRASE'` or `--add 'WORD=PHRASE'` Adds a new abbreviation, where WORD will be expanded to PHRASE. Only a single argument is supported - protect the contents with quotes or escapes.
+
+- `-s` or `--show` Show all abbreviated words and their expanded phrases in a manner suitable for export and import.
+
+- `-l` or `--list` Lists all abbreviated words.
+
+- `-r WORD` or `--remove WORD` Remove the abbreviation WORD.
+
+\subsection abbr-example Examples
+
+\fish
+abbr -a 'gco=git checkout'
+\endfish
+Add a new abbreviation where `gco` will be replaced with `git checkout`.
+
+\fish
+abbr -r gco
+\endfish
+Remove the `gco` abbreviation.
+
+\fish
+ssh another_host abbr -s | source
+\endfish
+Import the abbreviations defined on another_host over SSH.

share/completions/abbr.fish

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+complete -c abbr -f -s a -l add -d 'Add abbreviation'
+complete -c abbr -s r -l remove -d 'Remove abbreviation' -xa '(abbr -l)'
+complete -c abbr -f -s s -l show -d 'Print all abbreviations'
+complete -c abbr -f -s l -l list -d 'Print all abbreviation names'
+complete -c abbr -f -s h -l help -d 'Help'

share/functions/abbr.fish

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+function abbr --description "Manage abbreviations"
+	if test (count $argv) -lt 1 -o (count $argv) -gt 2
+		printf ( _ "%s: Expected one or two arguments, got %d\n") abbr (count $argv)
+		__fish_print_help abbr
+		return 1
+	end
+
+	switch $argv[1]
+		case '-a' '--add'
+			if __fish_abbr_get_by_key "$argv[2]" >/dev/null
+				printf ( _ "%s: abbreviation %s already exists\n" ) abbr (__fish_abbr_print_key "$argv[2]" )
+				return 2
+			end
+			set -U fish_user_abbreviations $fish_user_abbreviations "$argv[2]"
+			return 0
+
+		case '-r' '--remove'
+			set -l index (__fish_abbr_get_by_key "$argv[2]")
+			if test $index -gt 0
+				set -e fish_user_abbreviations[$index]
+				return 0
+			else
+				printf ( _ "%s: no such abbreviation %s\n" ) abbr (__fish_abbr_print_key "$argv[2]" )
+				return 3
+			end
+
+		case '-s' '--show'
+			for i in $fish_user_abbreviations
+				echo abbr -a \'$i\'
+			end
+			return 0
+
+		case '-l' '--list'
+			for i in $fish_user_abbreviations
+				__fish_abbr_print_key $i
+			end
+			return 0
+
+		case '-h' '--help'
+			__fish_print_help abbr
+			return 0
+
+		case '' '*'
+			printf (_ "%s: Unknown option %s\n" ) abbr $argv[1]
+			__fish_print_help abbr
+			return 1
+	end
+end
+
+function __fish_abbr_printable
+	echo (__fish_abbr_print_key $argv)'="'(echo $argv | cut -f 2 -d =)'"'
+end
+
+function __fish_abbr_get_by_key
+	for i in (seq (count $fish_user_abbreviations))
+		switch $fish_user_abbreviations[$i]
+			case (__fish_abbr_print_key $argv)'=*'
+				echo $i
+				return 0
+		end
+	end
+	echo 0
+	return 1
+end
+
+function __fish_abbr_print_key
+	echo $argv| cut -f 1 -d =
+end