主页 / unix / 问题 / 419815
Accepted
smarber
Asked: 2018-01-27 03:06:54 +0800 CST

Makefile 规则中的算术运算

  • 772

我需要在 bash 循环中执行算术运算，如下所述

CYCLE?=3
COUNT=1

download_when_ready: ## Will try the download operations many times till it succeeds or it reaches 10 tries
    while ! composer update $(bundle) 2> /dev/null && [[ $(COUNT) -lt 10 ]]; \
    do \
        COUNT=$$(( $(COUNT)+1 )); \
        SLEEP=$$(( ($(COUNT) / $(CYCLE)) + ($(COUNT) % $(CYCLE)) )); \
        echo "count $(COUNT)"; \
        echo "cycle $(CYCLE)"; \
        echo "sleep $(SLEEP)"; \
        sleep $(SLEEP); \
    done

这永远不会停止并给出以下内容：

count 0
cycle 4
sleep 0

count 0
cycle 4
sleep 0

....

count 0
cycle 4
sleep 0

如您所见，变量具有初始值并且永远不会改变！

更新

PRETTY_NAME="SUSE Linux Enterprise Server 11 SP4"

但是，以下代码$$c在 while 循环之前和内部保持空值。

CYCLE?=3
COUNT=1

download_when_ready: ## Will try the download operations many times till it succeeds or it reaches 10 tries
    @c=$(COUNT);
    @echo $$c;
    while ! composer update $(bundle) 2> /dev/null && [[ $(COUNT) -lt 10 ]]; \
    do \
        echo "$$c"; \
    done
bash make

1 个回答

  1. Best Answer

    更新

    感谢@Kusalananda 的评论，我明白了。

    我使用变量作为变量的初始值

    CYCLE?=3
COUNT=1

download_when_ready: ## Will try the download operations many times till it succeeds or it reaches 10 tries
    while ! composer update $(bundle) 2> /dev/null && [ "$$c" -lt 10 ]; \
    do \
        c=$$(( $${c:-$(COUNT)}+1 )); \
        s=$$(( ($$c / $(CYCLE)) + ($$c % $(CYCLE)) )); \
        echo "count $$c"; \
        echo "cycle $(CYCLE)"; \
        echo "sleep $$s"; \
        sleep $$s; \
    done

    这确实有效！

    count 1
cycle 4
sleep 1
count 2
cycle 4
sleep 2
count 3
cycle 4
sleep 3
count 4

    感谢@Kusalananda和@Stéphane Chazelas

    • 4

相关问题