Python子进程，mysqldump和管道 [英] Python subprocess, mysqldump and pipes

问题描述

尝试构建简单的备份/升级数据库脚本时遇到问题.

I've got a problem trying to build a easy backup/upgrade database script.

错误发生在使用子进程的mysqldump调用中:

The error is in the mysqldump call using subprocess:

cmdL = ["mysqldump", "--user=" + db_user, "--password=" + db_pass, domaindb + "|", "gzip", ">", databases_path + "/" + domaindb + ".sql.gz"]
print "%s: backup database %s \n\t[%s]" % (domain, domaindb, ' '.join(cmdL))
total_log.write("%s: backup database %s \n\t[%s] \n" % (domain, domaindb, ' '.join(cmdL)))
p = subprocess.Popen(cmdL, stdout=subprocess.PIPE, stderr=subprocess.STDOUT)

在开始之前，我将sys.stdout和sys.stderr重定向到文件，以便具有日志系统.

Before that cose, i redirect sys.stdout and sys.stderr to files, in order to have a log system.

在那些日志中，我发现了错误:

In those log, i find the error:

[mysqldump --user = xxxxxx --password = yyyyyyyy database_name | gzip>/home/drush-backup/2010-08-30.15.37/db/database_name.sql] [错误]:mysqldump:找不到表:"|"

[mysqldump --user=xxxxxx --password=yyyyyyyy database_name | gzip > /home/drush-backup/2010-08-30.15.37/db/database_name.sql] [Error]: mysqldump: Couldn't find table: "|"

似乎|字符被视为mysqldump参数，而不是管道.

Seem that the | character is seen as an mysqldump arguments, instead as a pipe.

查看python子进程文档，这很正常，但是我如何获取所需的信息(调用命令mysqldump --user=xxxxxx --password=yyyyyyyy database_name | gzip > /home/drush-backup/2010-08-30.15.37/db/database_name.sql)?

Looking into the python subprocess documentation, this is normal, but how can i obtain what i need (call the command mysqldump --user=xxxxxx --password=yyyyyyyy database_name | gzip > /home/drush-backup/2010-08-30.15.37/db/database_name.sql)?

编辑，我只是在python文档上看到以下示例:

EDIT I just see this example on python docs:

output=`dmesg | grep hda`
==>
p1 = Popen(["dmesg"], stdout=PIPE)
p2 = Popen(["grep", "hda"], stdin=p1.stdout, stdout=PIPE)
output = p2.communicate()[0]

并且我已经编辑了我的脚本:

and i've edit my script:

command = ["mysqldump", "--user=" + db_user, "--password=" + db_pass, domaindb, "|", "gzip", ">", databases_path + "/" + domaindb + ".sql.gz"]
cmdL1 = ["mysqldump", "--user=" + db_user, "--password=" + db_pass, domaindb]
cmdL2 = ["gzip", ">", databases_path + "/" + domaindb + ".sql.gz"]

print "%s: backup database %s \n\t[%s]" % (domain, domaindb, ' '.join(command))
total_log.write("%s: backup database %s \n\t[%s] \n" % (domain, domaindb, ' '.join(command)))

p1 = subprocess.Popen(cmdL1, stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
p2 = subprocess.Popen(cmdL2, stdin=p1.stdout, stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
cmdError, cmdData = p2.communicate()

现在命令变量只是为了方便日志使用.

now the command variable is just used for convenience in logs.

下一步，但它在>流中停止，出现以下错误:

This go a step next but it stops in the > stream, with this error:

[Error]: gzip: >: No such file or directory
gzip: /path/to/backups/dir/natabase_name.sql.gz: No such file or directory

很显然，如果我在终端中尝试该命令，它将起作用.

Obviously, if i try the command in a terminal it works.

推荐答案

我不确定管道的解释方式.如果有问题，可以以编程方式创建pipelilne.

I'm not sure of how the pipe will get interpreted. If that's a problem, you can programatically create a pipelilne.

来自: http://docs.python.org/library/subprocess.html#替换壳管道

p1 = Popen(["dmesg"], stdout=PIPE)
p2 = Popen(["grep", "hda"], stdin=p1.stdout, stdout=PIPE)
output = p2.communicate()[0]

编辑

对于文件重定向，您可以将stdout定向到文件.

As for file redirection, you can direct stdout to a file..

stdin，stdout和stderr指定 执行程序的标准输入， 标准输出和标准误差 文件句柄.有效的 值是PIPE，一个现有文件 描述符(一个正整数)，一个 现有文件对象，而没有.

stdin, stdout and stderr specify the executed programs’ standard input, standard output and standard error file handles, respectively. Valid values are PIPE, an existing file descriptor (a positive integer), an existing file object, and None.

示例:

out_file = open(out_filename, "wb")
gzip_proc = subprocess.Popen("gzip", stdout=out_file)
gzip_proc.communicate()

或者，如果您接受Alex的建议并使用Python的标准库 gzip 模块，可以做这样的事情:

or if you take Alex's advice and use Python's standard library gzip module, you can do something like this:

import gzip
import subprocess

...
#out_filename = path to gzip file

cmdL1 = ["mysqldump", "--user=" + db_user, "--password=" + db_pass, domaindb]
p1 = subprocess.Popen(cmdL1, stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
dump_output = p1.communicate()[0]

f = gzip.open(out_filename, "wb")
f.write(dump_output)
f.close()

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