bash 算术表达式：期望主要：
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arithmetic expression: expecting primary:
提问by Luis de la Fuente Nieto
I am trying to do a script in shell that sleeps for a random period of time and after this calls a python script. I am doing this:
我正在尝试在 shell 中执行一个脚本，该脚本会随机休眠一段时间，然后调用 python 脚本。我正在这样做：
#!/bin/bash
now="$(date)"
printf "Current date and time %s\n" "$now"
maxdelay=25
delay=$(($RANDOM%maxdelay)) # pick an independent random delay for each of the 20 runs
echo $delay;
(sleep $((delay*60)); /usr/bin/python pythonscript.py) &
But it is failing, this is the result:
但它失败了，这是结果：
Current date and time mar jun 9 00:02:10 CEST 2015
prueba.sh: 7: prueba.sh: arithmetic expression: expecting primary: "%maxdelay"
Yesterday it works perfect but today I don't know why it is failing
昨天它工作得很好，但今天我不知道为什么它失败了
回答by rici
You seem to be running that script using dashinstead of bash, possibly because you're invoking the script as
您似乎正在使用dash而不是运行该脚本bash，可能是因为您正在调用脚本
sh prueba.sh
instead of
代替
# prueba.sh must have exec permissions
# the shebang line is used to select the interpreter
./prueba.sh
or
或者
bash prueba.sh
RANDOMis a bash extension; in dash, it is not special and not assigned by default.
RANDOM是一个 bash 扩展；in dash，它并不特殊，默认情况下不分配。
In an arithmetic expression, if $varis used and varis unassigned, then it is substituted with an empty string, which often creates a syntax error. On the other hand, if you use varand varhas not been assigned a value, it is assumed to be 0.
在算术表达式中，如果$var使用var且未赋值，则将其替换为空字符串，这通常会产生语法错误。另一方面，如果您使用var和var尚未分配值，则假定为 0。
Debian and Ubuntu installs typically use dashfor the /bin/shdefault shell interpreter.
Debian 和 Ubuntu 安装通常dash用于/bin/sh默认 shell 解释器。
Note that bashand dashproduce different error messages:
请注意，bash并dash产生不同的错误消息：
$ bash -c 'unset foo;bar=25;echo $(($foo*$bar))'
bash: *25: syntax error: operand expected (error token is "*25")
$ dash -c 'unset foo;bar=25;echo $(($foo*$bar))'
dash: 1: arithmetic expression: expecting primary: "*25"
