Python中subprocess.Popen的奇怪现象

1. subprocess.Popen()中第一个参数传字符串

1.1 不带shell参数

subprocess.Popen('head -5 123.txt')			# 此句不管同级目录下有没有123.txt文件都会报错
FileNotFoundError: [Errno 2] No such file or directory: 'head -5 123.txt': 'head -5 123.txt'

1.2 subprocess.Popen()中第一个参数传字符串加参数shell=False

subprocess.Popen('head -5 123.txt', shell=False)			# 此句不管同级目录下有没有123.txt文件都会报错
FileNotFoundError: [Errno 2] No such file or directory: 'head -5 123.txt': 'head -5 123.txt'

1.3 subprocess.Popen()中第一个参数传字符串加参数shell=True

subprocess.Popen('head -5 123.txt', shell=True)			# 正常输出
total 20
drwxr-xr-x 4 hwd hwd 4096 Nov 29 22:33 .
drwxr-xr-x 4 hwd hwd 4096 Nov 29 21:31 ..
-rw-r--r-- 1 hwd hwd    0 Nov 29 22:34 123.txt
drwxr-xr-x 3 hwd hwd 4096 Nov 29 22:17 .idea

2. subprocess.Popen()中第一个参数传列表

2.1 不带shell参数

subprocess.Popen(['head', '-5', '123.txt'])			# 输出正常
total 20
drwxr-xr-x 4 hwd hwd 4096 Nov 29 22:33 .
drwxr-xr-x 4 hwd hwd 4096 Nov 29 21:31 ..
-rw-r--r-- 1 hwd hwd    0 Nov 29 22:34 123.txt
drwxr-xr-x 3 hwd hwd 4096 Nov 29 22:17 .idea

2.2 subprocess.Popen()中第一个参数传字符串加参数shell=False

subprocess.Popen(['head', '-5', '123.txt'], shell=False)			# 输出正常
total 20
drwxr-xr-x 4 hwd hwd 4096 Nov 29 22:33 .
drwxr-xr-x 4 hwd hwd 4096 Nov 29 21:31 ..
-rw-r--r-- 1 hwd hwd    0 Nov 29 22:34 123.txt
drwxr-xr-x 3 hwd hwd 4096 Nov 29 22:17 .idea

2.3 subprocess.Popen()中第一个参数传字符串加参数shell=True

subprocess.Popen(['head', '-5', '123.txt'], shell=True)			# 不报错，也不输出