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Ideas for Future Deprecations

These are some ideas, extracted from Shell Language Deprecations.

These breakages may never happen, as they require a significant new lexer mode. If they do, you will want to avoid the following syntax:

• r' and c' at the beginning of a word
• the character sequences $/, ''', """ anywhere

I expect that those sequences are rare, so this change would break few programs.

Raw and C String Literals in Word Mode

We might want to make string literals in the command/word context match Oil's expressions. This means we have to disallow implicit concatenation, or certain instances of it.

No:

var x = foo'bar'   # Not a valid Oil expression
echo foo'bar'      # Valid in shell, but discouraged

Yes:

var x = 'foobar'
echo 'foobar'

We don't want to break these, so = could be special

ls --foo='with spaces'
ls --foo="with $var"

New raw and C strings (which technically conflict with shell):

echo r'\'   # equivalent to '\'
echo c'\n'  # equivalent to $'\t'

Multiline Strings and Redirects

Instead of here docs:

cat <<EOF
hello
there, $name
EOF

cat <<'EOF'
$5.99  # no interpolation
'EOF'

We could have multiline strings:

cat << """
hello
there, $name
"""

cat << '''
$5.99  # no interpolation
'''

Minor breakage: the ''' and """ tokens become significant. It may also be nice to change the meaning of << slightly.

First Class File Descriptors (parse_amp)

We want to make redirection simpler and more consistent. We can remove the confusing <& and >& operators, and instead use > and < with descriptors.

Remains the same:

echo foo >file
read :var <file

Old:

echo foo >& 2
read var <& 0

New:

echo foo > &2         # descriptor with &
read :var < &0

echo foo > &stderr    # named descriptor
read :var < &stdin

Old:

echo foo 1>& 2

New:

echo foo &1 > &2

(Note: the syntax {fd}> file.txt will be replaced by the open builtin.)

https://github.com/oilshell/oil/issues/673

Inline Eggex

Instead of:

var pat = / digit+ /
egrep $pat *.txt

You can imagine:

egrep $/ digit+ / *.txt

Minor breakage: making $/ significant.

Bare Function Call

Instead of

call f()
call g(x, y)

You could do:

f()   # calls a func, doesn't begin a shell function declaration
g(x, y)

• This change probably doesn't involve a lexer mode.
• It would be a big breakage!