subprocess.Popen产生错误，而命令在命令行中运行顺畅（错误：查找：路径必须在表达式之前）

Question

I am trying to incorporate a few commands into a python script that I typically would use in a command line (Ubuntu 14.04) to deal with files.

I tried following the example on the subprocess help page , but it hits me with the following error message:

find: paths must precede expression: |
Usage: find [-H] [-L] [-P] [-Olevel] [-D help|tree|search|stat|rates|opt|exec] [path...] [expression]

The reason, I am a little stumped is that it excutes properly, if I type it directly in the console. I am suspecting there is something wrong how the arguments are parsed, but imo the printed out results for argv1 and argv2 to looked like expected (based on the example).

import subprocess, shlex



cmd1 = "find . -name *.tgz | xargs -i pigz -dv {}"
cmd2 = "find . -name *.tar | xargs -i tar -xfv {} -C decompressed --wildcards '*B5.TIF' '*B6.TIF' '*B8.TIF' "

args1 = shlex.split(cmd1)
args2 = shlex.split(cmd2)

print args1
print args2 

subprocess.call(args1)
subprocess.call(args2)

I tried subprocess.call() and subprocess.Popen() with the same results. Any suggestions are greatly appreciated.

Answer 1

subprocess.Popen(args1,shell=True) or subprocess.call(args1,shell=True) with shell=True works fine on Ubuntu 14.04 for me.

Warning Executing shell commands that incorporate unsanitized input from an untrusted source makes a program vulnerable to shell injection, a serious security flaw which can result in arbitrary command execution. For this reason, the use of shell=True is strongly discouraged in cases where the command string is constructed from external input :

Answer 2

I believe you're running into this error because of the pipes in your commands.

You'll want to do something like this instead (this is just for cmd1):

cmd1=`find . -name *.tgz | xargs -i pigz -dv {}`
# should instead be
p1 = subprocess.Popen(["find", ".", "-name", "*.tgz"], stdout=subprocess.PIPE)
p2 = subprocess.Popen(["xargs", "-i", "pigz", "-dv", "{}"], stdin=p1.stdout, stdout=subprocess.PIPE)
p1.stdout.close()  # Allow p1 to receive a SIGPIPE if p2 exits.
output = p2.communicate()[0]

For more details read the subprocess documentation .