解释bash脚本中set -e与set -o pipefail的作用

Posted 2022-06-03 t0nsha

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：

#!/bin/bash
# testset.sh
echo 'disable exit on non-zero return status and pipefail track'
set +e
set +o pipefail
a=$[1/0]|b=2
echo 'return status = '$?

echo 'disable exit on non-zero return status but enable pipefail track'
set +e
set -o pipefail
a=$[1/0]|b=2
echo 'return status = '$?

echo 'enable exit on non-zero return status and pipefail track'
set -e
set -o pipefail
a=$[1/0]|b=2
echo 'return status = '$?

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