get pid of pipeline command in background

发表于 分类于
本文字数： 1.7k 阅读时长 ≈ 2 分钟

get exit code of pipeline command in background

https://stackoverflow.com/questions/37257668/get-exit-code-of-a-piped-background-process

https://stackoverflow.com/questions/35842600/tee-resets-exit-status-is-always-0

1
2
3
4
5
6
7
8
9
someCommand="python test.py"

{
  ${someCommand} 2>&1 | tee -a training.log
  exit ${PIPESTATUS[0]}
} &

wait $!
echo $?

回显

1
127

综上 wait 即使指定的是 pid，然而内部代码实现依然会 wait pid 对应的 job，这点 wait 的文档里边说的比较隐晦

https://www.gnu.org/software/bash/manual/html_node/Job-Control-Builtins.html

Wait until the child process specified by each process ID pid or job specification jobspec exits and return the exit status of the last command waited for.

注意 return the exit status of the last command waited for

所以上述代码，wait 命令实际上获取到的是 tee 命令的退出码

在 shell 中获取 pipeline command status 的简易方法似乎只能通过 ${PIPESTATUS[0]}

get pid of pipeline command in background

进一步的，我们想获取 someCommand 的 pid，有办法么，尝试做如下改造

1
2
3
4
5
6
7
8
9
10
11
someCommand="python test.py"

{
    ${someCommand} 2>&1 &
    pid_someCommand=$!
    wait ${pid_someCommand}
    exit $?
} | tee -a training.log &

wait $!
echo ${PIPESTATUS[0]}

回显

1
0

but not work

最后只能使用 ps -ef | grep someCommand 的终极大法，加上通过 subshell pid 作为 parent id 过滤

1
2
3
4
5
6
7
8
9
10
11
12
13
someCommand="python test.py"

{
  ${someCommand} 2>&1 | tee -a training.log
  exit ${PIPESTATUS[0]}
} &
someCommand_job_pid=$!

someCommand_pid=`ps -efj | awk -v parent_pid=${someCommand_job_pid} '$3==parent_pid { print $0 }' | grep "${someCommand}" | awk '{ print $2 }'`
echo someCommand_pid ${someCommand_pid}

wait ${someCommand_job_pid}
echo $?

回显

1
2
someCommand_pid 55863
127

test.py

1
2
3
4
5
import time
import sys

time.sleep(5)
sys.exit(127)