R - 具有多个管道的系统命令不return stdout

Question

bash:

ps -aux | grep -E "^.*\b[^grep](python).*(runserver).*$" 2>/dev/null | tr -s " " | cut -d " " -f 2

这是 return 正确的结果。（例如）

1450
1452

R 中的相同代码

vLog <- system('ps -aux | grep -E "^.*\b[^grep](python).*(runserver).*$" 2>/dev/null | tr -s " " | cut -d " " -f 2', intern = TRUE)

return character(0)

Answer 1

只需将 \b 替换为 \b 并注意 [^grep] 匹配任何字符但不匹配 g 或 r 或 e 或 p.

vLog <- system('ps -aux | grep -E "^.*\b[^grep](python).*(runserver).*$" 2>/dev/null | tr -s " " | cut -d " " -f 2', intern = TRUE)

示例：

> system('ps -aux | grep -E "^.*\bpython" 2>/dev/null | tr -s " " | cut -d " " -f 2', intern = TRUE)
[1] "2519" "2526" "3285" "3291"
> system('ps -aux | grep -E "^.*\bpython" 2>/dev/null | tr -s " " | cut -d " " -f 2', intern = TRUE)
character(0)

R - 具有多个管道的系统命令不return stdout

R - system commands with multiple pipe do not return stdout

bash

r

system

pipe