Why Sponsor Oil? | source | all docs for version 0.13.1 | all versions | oilshell.org
This is an essential syntactic concept in Oil.
Oil is an extension of the shell language, which consists of commands. The most important addition is a Python-like expression language. To implement that, the lexer enters "expression mode".
Here's the key difference:
In command mode, unquoted
is a string, while $dollar
is a variable:
ls /bin/str $myvar
In expression mode: 'quoted'
is a string, while unquoted
is a variable:
var s = myfunc('str', myvar)
Here is a list of places we switch modes.
Everything after =
is parsed in expression mode:
var x = 42 + f(x) # RHS of var/setvar
setvar x += g(y)
setvar x = obj.method()
x = 'myconst'
=
and _
keywordsLikewise, everything after =
or _
is in expression mode:
= 42 + f(x)
Throw away the value:
_ L.append(x)
echo $[42 + a[i]]
echo $strfunc(1, 2, a[i])
echo @arrayfunc('three', 'four', f(x))
proc p(x, y) { # what's between () is in expression mode
echo $x $y # back to command mode
}
if
, while
, and for
Expressions appear inside ()
:
if (x > 0) {
echo 'positive'
}
while (x > 0) {
setvar x -= 1
}
for k, v in (mydict) {
echo "$k $v"
}
(The syntax of case
breaks this rule. It's a wart inherited from
shell.)
var myarray = %( /tmp/foo ${var} $(echo hi) @myarray )
Everything in between sigil pairs is in command mode:
var x = $(hostname | tr a-z A-Z)
var y = @(seq 3) # Split command sub
var b = &(echo $PWD)
No:
echo '*.py' # a literal string, not a glob
echo @glob(*.py) # syntax error, * is an operator in
# expression mode
var x = myfunc(*.py) # ditto, syntax error
Yes:
echo *.py # expanded as a glob
echo @glob('*.py') # A literal string passed to the builtin
# glob function
var x = f('*.py') # Just a string
var x = f(glob('*.py')) # Now it's expanded
Another way to say this is that Oil works like Python:
from glob import glob
glob('*.py') # this is a glob
os.listdir('*.py') # no glob because it's not how listdir() works
Also note that Oil has a builtin operator that uses glob aka fnmatch()
syntax:
if (x ~~ '*.py') { # not yet implemented
echo 'Python'
}