Get External variable contents in shell while

First, the question

The question is simple, look at the following section of tmp.sh code:

#!/bin/Shx= "This was theinitial value of x" while a read line;  Do         x= "$line"        = $x

/tmp/tmp's Content

1,a

Execute./tmp.sh, the normal x variable is the blue "1,a", but the actual result is the red part:

[Email protected] ~]$./1,aThis is theinitial value of x

The problem is obviously that the variable x is not brought outside after it has been modified in the while, why?

Second, the answer

After several searches, finally found the cause of the problem: because the child process is started, and the variable x after the child process has been modified, did not bring into the parent process. The original text reads as follows:

This was because in the Bourne shell redirected control structures run in a subshell, so the value of x only gets Chang Ed  in the for non-Bourne shells are to use redirectioninstead of the pipeline

How to solve?

1. General Method:

# !/bin/shx="This was theinitial value of x"while aread line;  Do         x="$line"        $x</tmp/  $x

Run:

[Qiu.li@l-tdata1.tkt.cn6 ~]$./tmp.  1,a1,a

2. Some elegant solutions:

#!/bin/shx="This is the initial value of x"exec 3<&0         #Save stdinexec</tmp/tmp while ReadLine Dox=$lineEcho$x Doneexec 0<&3        #Restore stdinecho x =$x

My English is really limited, the reason can only be posted in English:

#!/bin/sh at the top of a script doesn ' t  guarantee you ' re using the Bourne shell. Some Systems link/bin/sh to Some the other  shell. Check your system documentation to find out what the shell you ' re really getting in the this case.

Probably said: Note The top #!/bin/sh if you use the other this script cannot run. However, in some systems/bin/sh are assigned to the other shell interpreter, there is a different result. Detailed reference: http://www.cnblogs.com/liqiu/p/4107948.html

Get External variable contents in shell while