bash expr 计算变量（cygwin）
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bash expr calculation with variables (cygwin)
提问by Matthias
I am trying to calculate the difference between two unix timestamps. The calculation of 42-23 is for testing purposes only.
我正在尝试计算两个 unix 时间戳之间的差异。42-23 的计算仅用于测试目的。
# !/bin/bash
TARGET=1305281500
CURRENT=`date +%s`
echo $TARGET
echo $CURRENT
A=`expr 42 - 23`
B=`expr $TARGET - $CURRENT`
echo "A: $A"
echo "B: $B"
Output:
输出：
1305281500
1305281554
expr: non-integer argument
A: 19
B:
What is the problem with subtracting one variable from another? The script is working on a unix maschine. I am using Cygwin on Windows 7:
从另一个变量中减去一个变量有什么问题？该脚本正在使用 unix 机器。我在 Windows 7 上使用 Cygwin：
$ uname -a
CYGWIN_NT-6.1-WOW64 mypcname 1.7.9(0.237/5/3) 2011-03-29 10:10 i686 Cygwin
$ bash --version
GNU bash, version 4.1.10(4)-release (i686-pc-cygwin)
回答by Matthias
The problem was that I wrote the script on Windows with its system-specific line ending \r\n. After changing to the Unix line ending \n, it works.
问题是我在 Windows 上编写了脚本，其系统特定的行结尾是\r\n. 更改为 Unix 行结尾后\n，它可以工作。
回答by anubhava
You don't need to call exprfor this actually just use bash's $(( expr ))feature. On my cygwin this code is working fine:
您expr实际上不需要调用此$(( expr ))功能，只需使用 bash 的功能即可。在我的 cygwin 上，这段代码运行良好：
# !/bin/bash
TARGET=1305281500
CURRENT=`date +%s`
echo $TARGET
echo $CURRENT
B=$((CURRENT - TARGET))
echo "B: $B"
# For validation only
echo "$TARGET $CURRENT" | awk '{print (-)}'
And it gave this output:
它给出了这个输出：
B: 8316
8316
回答by tmg
Why not use $[] ?
为什么不使用 $[] ？
TARGET=1305281500
CURRENT=1305281554
A=$[42 - 23]
B=$[$TARGET - $CURRENT]
echo "A: $A"
echo "B: $B"A: 19
B: -54回答by Chang Peng
I don't see this problem on Linux here. But do you get the right answer with the line
我在这里在 Linux 上没有看到这个问题。但是你能得到正确的答案吗？
B=`expr $TARGET - $CURRENT`
replaced by
取而代之
B=`eval expr $TARGET - $CURRENT`
