求解：关于bash行命令解释的基本问题，有脚本例子

sanxiao

直接上脚本例子：
##### my_test.sh #####
#!/bin/bash
function my_fun()
{
    MY_VAR=abc \
    echo "$1$MY_VAR$1"
    MY_VAR=abc  echo "$1$MY_VAR$1"
    MY_VAR=abc  make -f my.mk
    echo $MY_VAR
}
my_fun hello

####### my.mk ######
# makefile : my.mk
TARGET := target-$(MY_VAR)

all:
    @echo $(TARGET)

执行my_test.sh，输出
hellohello
hellohello
target-abc

在 my_fun中，同一行内定义变量MY_VAR和执行echo命令，MY_VAR变量没有输出。第一和第二句是相同的，而第三句执行make程序，则变量有定义。

这是为什么呢？shell执行一行命令时有什么讲究或者玄机呢？

sanxiao

在线等了好久，没人理我吗

wtuter

回复 1# sanxiao


   看看基础先，没有玄机

blackold

回复 2# sanxiao


    答案在这里，慢慢看。http://bbs.chinaunix.net/viewthr ... p;extra=&page=1

sanxiao

回复 4# blackold


    多谢了，正是我想要的。

justlooks

AA=1 eval echo \$AA

1

blackold

有鬼？

sanxiao

多谢上面各位的答复，后又参考了man手册，摘录如下：

ENVIRONMENT
       When a program is invoked it is given an array of strings called the environment.  This is a list of name-value pairs, of
       the form name=value.

       The  shell  provides  several ways to manipulate the environment.  On invocation, the shell scans its own environment and
       creates a parameter for each name found, automatically marking it for  export  to  child  processes.   Executed  commands
       inherit  the  environment.   The export and declare -x commands allow parameters and functions to be added to and deleted
       from the environment.  If the value of a parameter in the environment is modified, the new  value  becomes  part  of  the
       environment,  replacing the old.  The environment inherited by any executed command consists of the shell's initial envi©\
       ronment, whose values may be modified in the shell, less any pairs removed by the unset command, plus any  additions  via
       the export and declare -x commands.

       The  environment  for  any simple command or function may be augmented temporarily by prefixing it with parameter assign©\
       ments, as described above in PARAMETERS.  These assignment statements affect only the environment seen by that command.

       If the -k option is set (see the set builtin command below), then all parameter assignments are placed in the environment
       for a command, not just those that precede the command name.

       When bash invokes an external command, the variable _ is set to the full file name of the command and passed to that com©\
       mand in its environment.

又学会了一点