bash文件中set -e和set -o potion-name的作用

man set中的解释：

       set [--abefhkmnptuvxBCEHPT] [-o option] [arg ...]

       set [+abefhkmnptuvxBCEHPT] [+o option] [arg ...]

... ...

              -e      Exit  immediately  if a pipeline (which may consist of a

                      single simple command),  a subshell command enclosed  in

                      parentheses,  or one of the commands executed as part of

                      a command list enclosed by  braces  (see  SHELL  GRAMMAR

                      above) exits with a non-zero status.  The shell does not

                      exit if the command that fails is part  of  the  command

                      list  immediately  following  a  while or until keyword,

                      part of the test  following  the  if  or  elif  reserved

                      words,  part  of any command executed in a && or ││ list

                      except the command following the final  &&  or  ││,  any

                      command  in a pipeline but the last, or if the command’s

                      return value is being inverted with !.  A trap  on  ERR,

                      if set, is executed before the shell exits.  This option

                      applies to the shell environment and each subshell envi-

                      ronment  separately  (see  COMMAND EXECUTION ENVIRONMENT

                      above), and may cause subshells to exit before executing

                      all the commands in the subshell.

... ...

              -o option-name

                      The option-name can be one of the following:

... ...

                      pipefail

                              If  set,  the  return value of a pipeline is the

                              value of the last (rightmost)  command  to  exit

                              with  a non-zero status, or zero if all commands

                              in the pipeline exit successfully.  This  option

                              is disabled by default.

.. ...

个人理解：

set -e表示一旦脚本中有命令的返回值为非0，则脚本立即退出，后续命令不再执行;

set -o pipefail表示在管道连接的命令序列中，只要有任何一个命令返回非0值，则整个管道返回非0值，即使最后一个命令返回0.

小实验：

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1. #!/bin/bash  
2. # testset.sh  
3. echo 'disable exit on non-zero return status and pipefail track'  
4. set +e  
5. set +o pipefail  
6. a=$[1/0]|b=2  
7. echo 'return status = '$?  
8.   
9. echo 'disable exit on non-zero return status but enable pipefail track'  
10. set +e  
11. set -o pipefail  
12. a=$[1/0]|b=2  
13. echo 'return status = '$?  
14.   
15. echo 'enable exit on non-zero return status and pipefail track'  
16. set -e  
17. set -o pipefail  
18. a=$[1/0]|b=2  
19. echo 'return status = '$?  

输出结果：

[root@desktop2 ~]# ./testset.sh 

disable exit on non-zero return status and pipefail track

./testset.sh: line 6: 1/0: division by 0 (error token is "0")

return status = 0

disable exit on non-zero return status but enable pipefail track

./testset.sh: line 12: 1/0: division by 0 (error token is "0")

return status = 1

enable exit on non-zero return status and pipefail track

./testset.sh: line 18: 1/0: division by 0 (error token is "0")

[root@desktop2 ~]# 

REF:

1. pipefail

http://petereisentraut.blogspot.com/2010/11/pipefail.html

2. linux中的set命令: "set -e" 与 "set -o pipefail" 

http://blog.chinaunix.net/uid-15007890-id-3493077.html

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