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YSH Language Warts

This documents describes parts of the YSH language that may be surprising.

All languages have warts, but most of them don't document them for you! Even a nice language like Python has surprising cases like 42, and f(x), being a 1-tuple (because of the trailing comma).

The goal of YSH is to remove the many warts of shell, documented at Shell WTFs. Nonetheless it has some of its own.

For Bash Compatibility

Two Left Parens Should be Separated By Space

No:

if ((x + 1) < n) {  # note ((
  echo 'less'
}

Yes:

if ( (x + 1) < n) {  # add a space
  echo 'less'
}

This is because the (( token is for bash arithmetic, which is disallowed in YSH.

Two Different Syntaxes For Block and Expr Literals

Blocks look different in command vs expression mode:

cd /tmp {                   # command mode { }
  echo $PWD
}
var myblock = ^(echo $PWD)  # expression mode, lazy ^( )

So do expressions:

myproc | where (age > 10)   # command mode, lazy ( )
var myval = age > 10        # expression mode
var myexpr = ^[age > 10]    # expression mode, lazy ^[ ]

It would have been nicer if they were consistent, but shell is already inconsistent with $(echo hi) and { echo hi; }.

There is consistency in other directions:

• ^(echo $PWD) is consistent with shell's eagerly evaluated $(echo $PWD).
• ^[42 + f(x)] is consistent with expression sub $[42 + f(x)].

Most users won't see these literal forms very much. They're more useful for testing and frameworks rather than simple scripts/applications.

Related

• The doc on compatibility quirks relates to the OSH language.