bash shell脚本中的for循环/if条件
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for loop / if condition in shell script
提问by mkn
I've never done shell script before and now I'm running into a simple problem... I have a for loop which executes every time the run.sh script. To see how far the script has already run I want to print e.g. every 5000 the actual index.
我以前从未做过 shell 脚本，现在我遇到了一个简单的问题......我有一个 for 循环，每次 run.sh 脚本时都会执行。要查看脚本已经运行了多远，我想打印例如每 5000 个实际索引。
$counter = 0
for (( i = 0 ; i <= 5000; i++ ))do
if ($i = $counter); then
echo "$counter"
counter=$(counter+1000)
fi
./run.sh
done
running this piece of code gives me the following error
运行这段代码给了我以下错误
./for_loop.sh: line 1: =: command not found
./for_loop.sh: line 3: 0: command not found
I have also tried to init the variable counter with
我也尝试用初始化变量计数器
declare -i counter = 0
which gives me the following error
这给了我以下错误
./for_loop.sh: line 1: declare: `=': not a valid identifier
回答by Derek Mahar
You don't really need two counters. A single counter will suffice:
你真的不需要两个计数器。一个计数器就足够了：
for (( counter = 0; counter <= 5000; counter++ ))
do
if (( counter % 1000 == 0 ))
then
echo "$(( counter / 1000 ))"
fi
./run.sh
done
This executes run.sh5000 times and prints the counter value every 1000 iterations. Note that %is the modulus operator which computes remainder after division and /is the integer division operator.
这将执行run.sh5000 次并每 1000 次迭代打印计数器值。请注意，这%是计算除法后余数的模运算符，并且/是整数除法运算符。
回答by schot
Line 1 should be: (No $, no extra spaces around '=')
第 1 行应该是：（没有 $，'=' 周围没有多余的空格）
counter=0
Line 3 should be: (Square brackets, '-eq' because '=' is for string equality)
第 3 行应该是：（方括号，'-eq' 因为 '=' 用于字符串相等）
if [ $i -eq $counter ]
Line 5 should be: (Double parentheses)
第 5 行应该是：（双括号）
counter=$((counter+1000))
回答by Jed Schneider
In line 3 I believe you have mistaken assignment =for equality ==
在第 3 行中，我相信您将分配错误地视为=平等==
http://www.gnu.org/software/bash/manual/bashref.html#Shell-Arithmetic
http://www.gnu.org/software/bash/manual/bashref.html#Shell-Arithmetic
