Simple question for all of you python gurus

[Sean Berry]

I am writing a little script to grep through a really long list of files and
look for a certain phrase.

I wanted to do something like this.

li = os.popen("/usr/bin/grep -i %s /home/%s/.tmda/pending" %(phrase,userid)
lis = li.readlines()
blah blah blah...

but even if I run this from the command line I get an error saying the
argument list is too long.

However, if I cd to /home/userid/.tmda/pending and then run the grep from
within the directory... it works great.

so I tried to do something like this
os.system("cd /home/%s/.tmda/pending" %userid)
li = os.popen("/usr/bin/grep -i %s" %phase)
lis = lis.readlines()

But since cd is a shell command, it does not seem to work either.

How can I do this?
Thanks in advance for answering this seemingly easy question.

 

[Sean Berry]

Thanks to you both.

os.chdir ... I knew it was something simple. Sorry for the wasted
bandwidth.

 

[Diez B. Roggisch]

How can I do this?

Thanks in advance for answering this seemingly easy question.

You're code might work if you use os.chdir to change the current working
directory.

Another that works on the command-line (and thus for your script) is to use
xargs with -l<num>, e.g.:

find / | xargs -l 10 grep -i foo

xargs then will invoke grep in batches of ten.

 

[Cameron Laird]

.
.
.

so I tried to do something like this
os.system("cd /home/%s/.tmda/pending" %userid)
li = os.popen("/usr/bin/grep -i %s" %phase)
lis = lis.readlines()

But since cd is a shell command, it does not seem to work either.

How can I do this?

.
.
.
import os

os.chdir("/home/%s/.tmda/pending" % userid)
li = os.popen(...

 

[Jeremy Sanders]

os.chdir("/home/%s/.tmda/pending" % userid)
li = os.popen(...

Wouldn't something like this also work?

li = os.popen('/bin/sh -c "cd /home/%s; /usr/bin/grep -i %s blah"')

This has the advantage that the current directory of the Python program
doesn't change.

Jeremy

 

[Cameron Laird]

Wouldn't something like this also work?

li = os.popen('/bin/sh -c "cd /home/%s; /usr/bin/grep -i %s blah"')

This has the advantage that the current directory of the Python program
doesn't change.

.
.
.
Yes.

I want to make it explicit: yes, "/bin/sh -c ..." *does* work,
it's a good technique to keep in mind, and it does have the
advantage you describe (assuming proper resolution of the %s-s
above).

Even for Python, there frequently are multiple solutions. I
speculated that the original poster would feel most comfortable
with os.chdir(), and choose not to mention other possibilities.

As valuable as "/bin/sh -c ..." is, some people avoid it for
its Unix-specificity, or even its multiplication of process
count.