From: Peter Stephenson <p.w.stephenson@ntlworld.com>
To: zsh-users@zsh.org
Subject: Re: Variable fails to increment with lvalue error
Date: Mon, 23 Oct 2023 17:43:57 +0100 (BST) [thread overview]
Message-ID: <1372623164.1448847.1698079437641@mail.virginmedia.com> (raw)
In-Reply-To: <CAN=4vMo17fU8fwL55UnQQLR2TfqYRPdjUoY4fLs_Mdfjp-_0Pw@mail.gmail.com>
> On 23/10/2023 16:33 Roman Perepelitsa <roman.perepelitsa@gmail.com> wrote:
> On Mon, Oct 23, 2023 at 5:28 PM Evan Clearfield <efclear@gmail.com> wrote:
> >
> > I then increment it with a simple call “(($count++))”, and when I run the script, I receive the error “bad math expression: lvalue required”
>
> `$count` expands to `0`, so `(($count++))` is equivalent to `((0++))`.
Is it worth drawing attention to this, or is this just excess verbiage?
pws
diff --git a/Doc/Zsh/arith.yo b/Doc/Zsh/arith.yo
index bc3e35ad5..e6380b2cb 100644
--- a/Doc/Zsh/arith.yo
+++ b/Doc/Zsh/arith.yo
@@ -23,8 +23,10 @@ command which begins with a `tt(LPAR()LPAR())', all the characters until a
matching `tt(RPAR()RPAR())' are treated as a double-quoted expression and
arithmetic expansion performed as for an argument of tt(let). More
precisely, `tt(LPAR()LPAR())var(...)tt(RPAR()RPAR())' is equivalent to
-`tt(let ")var(...)tt(")'. The return status is 0 if the arithmetic value
-of the expression is non-zero, 1 if it is zero, and 2 if an error occurred.
+`tt(let ")var(...)tt(")': note the presence of double quotes, so that variable
+expansion etc. takes place before arithmetic evaluation. The return
+status is 0 if the arithmetic value of the expression is non-zero, 1 if
+it is zero, and 2 if an error occurred.
For example, the following statement
@@ -37,6 +39,10 @@ example(let "val = 2 + 1")
both assigning the value 3 to the shell variable tt(val) and returning a
zero status.
+Note further that it would be incorrect to replace tt(val) with tt($val)
+as the latter is affected by double quote substitution, so that
+arithmetic evaluation does not see the name of the variable.
+
cindex(arithmetic base)
cindex(bases, in arithmetic)
Integers can be in bases other than 10.
next prev parent reply other threads:[~2023-10-23 16:45 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-10-23 15:27 Evan Clearfield
2023-10-23 15:33 ` Roman Perepelitsa
2023-10-23 16:43 ` Peter Stephenson [this message]
2023-10-23 17:03 ` Roman Perepelitsa
2023-10-23 18:21 ` Ray Andrews
2023-10-23 16:34 ` Dominik Vogt
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