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Content Tagged with shell + python

Cloud User Shell (cush) is a multi-call executable (like BusyBox) that combines many useful cloud computing utilities into a single utility, bringing cushy, RESTful cloud control to the command line.

It follows Unix principles, seamlessly blending cloud resources into existing working environments. In addition to bringing basic HTTP verbs (get, put, post, delete) to the shell, it allows URLs to be ‘dereferenced’ and software pipelines of server side software to be created.

Most people will create a link to cush for each function they wish to use and cush will act like whatever it was invoked as, but it can also be called directly and passed the command as the first parameter.

I just read the following post Python - Script - Which Webserver Does That Site Run? by blogger Corey Goldberg.

I prefer the shell version:

$ what-http-server() { curl -s -I "http://$1" | awk -F': ' '/^Server:/ {print $2}'; }
$ what-http-server www.pylot.org
Apache/2.0.52
$ what-http-server() { curl -s -I "$@" | awk -F': ' '/^Server:/ {print $2}'; }
$ what-http-server www.pylot.org google.com bashcurescancer.com
Apache/2.0.52
gws
Apache/2.2.6 (Unix)

That works but this version is more correct:

what-http-server() { curl -s -I $(for h in "$@"; do printf "http://%s " "$h"; done) | awk -F': ' '/^Server:/ {print $2}'; }

In the version which works for multiple hosts, we are letting curl assume the protocol is HTTP. This works fine most of the time. However, there are exceptions:

If you specify URL without protocol:// prefix, curl will attempt to guess what protocol you might want. It will then default to HTTP but try other protocols based on often-used host name prefixes. For example, for host names starting with “ftp.” curl will assume you want to  speak FTP. - man curl

There are situations where, if you want a Python, PERL, PHP, etc script to be portable among a few different servers, it makes sense to wrap the script in shell. A few years ago I was trying to use the Python cx_Oracle module. This module is a wrapper for the native Oracle database driver. However, it requires the driver library directory be in the LD_LIBRARY_PATH environment variable.

No problem I thought. I’ll use the os.environ dict to set the variable.  Example script:

$ cat python-only.sh
#!/usr/bin/python
import sys, os
sys.path.append("/usr/local/lib/python2.4/site-packages/")
if not os.environ.has_key('LD_LIBRARY_PATH'):
        os.environ['LD_LIBRARY_PATH'] = "/home/noland/oracle-lib"
else:
        os.environ['LD_LIBRARY_PATH'] = "/home/noland/oracle-lib:" + os.environ['LD_LIBRARY_PATH']
print "LD_LIBRARY_PATH looks OK in Python: LD_LIBRARY_PATH = ", os.environ['LD_LIBRARY_PATH']
os.system('echo LD_LIBRARY_PATH looks OK via os.system: LD_LIBRARY_PATH = $LD_LIBRARY_PATH')
try:
        import cx_Oracle
        print "Imported cx_Oracle! LD_LIBRARY_PATH was set correctly."
except ImportError, e:
        print "Woops, LD_LIBRARY_PATH was not set correctly: ", e

This method does not work:

$ ./python-only.sh
LD_LIBRARY_PATH looks OK in Python: LD_LIBRARY_PATH =  /home/noland/oracle-lib
LD_LIBRARY_PATH looks OK via os.system: LD_LIBRARY_PATH = /home/noland/oracle-lib
Woops, LD_LIBRARY_PATH was not set correctly:  libclntsh.so.10.1: cannot open shared object file: No such file or directory

This seems to be a common problem. However, when I was dealing with this a few years ago, I could not find a good resource on Google. I bite the bullet and wrote a separate shell script wrapper - hating invocation of the shell script. However, there is absolutely no reason I needed a separate shell script. I could have embedded the Python within a shell script. Example:

$ cat python-and-bash.sh
#/bin/bash
export LD_LIBRARY_PATH=/home/noland/oracle-lib:$LD_LIBRARY_PATH
/usr/bin/python<<END_OF_PYTHON
import sys
sys.path.append("/usr/local/lib/python2.4/site-packages/")
try:
        import cx_Oracle
        print "Imported cx_Oracle! LD_LIBRARY_PATH was set correctly."
except ImportError, e:
        print "Woops, LD_LIBRARY_PATH was not set correctly: ", e
END_OF_PYTHON

Ahh, much better:

$ ./python-and-bash.sh
Imported cx_Oracle! LD_LIBRARY_PATH was set correctly.

Of course I could have just set this variable in my profile. However, this creates an additional external dependency - which is what I was trying to avoid.