Delivery of data between commands in the shell

1. Piping "|"

ls | Cat-n > OUT.txt

2. Child shell

2.1 Child Shell Description

You can use the () operator to define a child shell in a shell script

#/bin// ; ls) pwd

Execution results

　　

Description: Does not have any effect on the current shell when the command executes in a child shell

2.2 Getting data from a child shell

cmd_output=$ (COMMANDS)

out=$ (ls-l | cat-n)

#!/bin/bashout=$ (lscat -N)echo $out

Output Result:

　　

The problem: the return key between rows and rows is gone. This is obviously the result we don't want.

　　Workaround: Enclose the result of the child shell in double quotes, preserving line breaks

　　

#!/bin/bashout=$ (lscat -N)echo  $outout="$ ( Ls-l | cat-n)"echo $out

Execution Result:

　　

What the heck!!! There is no change. Is it wrong to write in the book?!

Finally found the answer to the question on the Internet: IFS (internal domain delimiter)

IFS Details: http://www.2cto.com/os/201504/394478.html

The IFS is set to "\ n" line breaks.

　　

#!/bin/bashout=$ (lscat -N)echo  $outIFS="\ n  "out ="$ (ls-l | cat-n)"echo $out

　　

3. Anti-citation (not a single quote)

out.txt= ls | Cat-n

Other operations are the same as child shells

Delivery of data between commands in the shell