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Mac Forum / Programming / Perl / August 2005The shell and my scripts
Recently there was a change at work -- all http access now needs to go through a proxy. So if I have a script using LWP::UserAgent or similar, I have to add $UA->proxy( ['http'] , 'http://proxy.fake.com:8080' ); to all my scripts. Which is a big pain. So a *NIX guy said "you shouldn't need to do that if you can add an environment variable to your shell". So, as I use tcsh, not bash, which is the default nowadays, I added this to .tcshrc: setenv http_proxy http://proxy.fake.com:8080 and it seemed to work, but leaving aside the specifics of the scripts, how would Perl "know" that I use tcsh, not bash? Isn't that a preference of the Terminal app, not of me as a user? A script run as a cron job, does it run using all the environment variables as if I'd typed its name into the Terminal? What about a script run from BBEdit? What if I "su root" and run it? I'd really appreciate someone explaining the relationship of script to shell and user. The environment variables have nothing to do with the shell. The only thing the shell does is give you a way to set environment variables, and different shells have different syntax for that. But environment variables are a property of your login session, not of the shell. So the short answer is: Perl does not need to know or care about what shell you're running in (although that's available as the environment variable SHELL). Perl scripts just get the environment variables for "free" as part of the startup. Hope that answers it. Kim Helliwell kimgh@mac.com Homepage: http://homepage.mac.com/kimgh > Recently there was a change at work -- all http access now needs to > go through a proxy. [quoted text clipped - 21 lines] > I'd really appreciate someone explaining the relationship of script > to shell and user. More to the point, environment variables are part of every process (rather than just a login session). A process inherits variables with values from the environment of its parent when it starts. From then on they're independent of the parent. They're not a bolt-on but a fundamental part of the Unix process design. David > The environment variables have nothing to do with the shell. > The only thing the shell does is give you a way to set environment [quoted text clipped - 38 lines] > > I'd really appreciate someone explaining the relationship of script > > to shell and user. > and it seemed to work, but leaving aside the specifics of the > scripts, how would Perl "know" that I use tcsh, not bash? As others have already said, Perl knows there's an environment variable, but it neither knows nor cares how that variable got set. > Isn't that a preference of the Terminal app, not of me as a user? Actually, no. It's a preference of the user. If you log in by other means - X11's xterm, or remotely through ssh, for instance - the same preference will be used. > A script run as a cron job, does it run using all the environment > variables as if I'd typed its name into the Terminal? No. As it says in "man 5 crontab", only LOGNAME (aka USER on some systems), HOME, and SHELL are set. You may set others by adding name=value pairs to your crontab file. See "man 5 crontab" for details. > What about a script run from BBEdit? BBEdit is a GUI app, and GUI apps don't use your login shell. To define environment variables to be used by GUI apps, have a look at this Q&A from Apple: <http://developer.apple.com/qa/qa2001/qa1067.html> > What if I "su root" and run it? It depends. If you simply "su" to root, you'll keep the same environment. But, if you "su -" (note the dash), it's like you're starting a separate new login session - root's own user login scripts are run, and nothing is inherited. Sudo begins with an inherited environment, but modifies it heavily - have a look at the "Security Notes" section in "man sudo" for details. sherm-- Cocoa programming in Perl: http://camelbones.sourceforge.net Hire me! My resume: http://www.dot-app.org >>What about a script run from BBEdit? > >BBEdit is a GUI app, and GUI apps don't use your login shell. To define environment variables to be used by GUI apps, have a look at this Q&A from Apple: BBEdit also allows BBEdit worksheets which are a bit like Apple's MPW using ENTER to execute selected text as shell commands. If you are using one of those an instance of your selected shell, tcsh, is associated with each open worksheet. On opening a worksheet your ~/.tcshrc is "sourced" and you can set environment variables there. Your tcsh login script is NOT run. It's probably better to create a $HOME/.MacOSX/environment.plist file but watch out for the public tcsh startup files in /etc/. As delivered they can overwrite your selections in the plist especially for $PATH. The plist is read only at login-to-Aqua time. If you change it you must logout and login again to see the changes. Things are better now that it's UNIX underneath. Just ask Steve.  Signature--> Halloween == Oct 31 == Dec 25 == Christmas <-- Thank you all for your help. I think I get it now. Just to clear up some confusion, when I'm working in BBEDit, I have two options to run the script: Run -- which seems to run the script in bash. Run In Terminal -- which runs in my chosen shell and I also run scripts from cron, using the Cronnix utility Here's a script: for(keys(%ENV)){ print "$_ == $ENV{$_}\n"; } Output of this script with BBEDit's "Run": ----- USER == myusername PATH == /usr/bin:/bin:/usr/sbin:/sbin:/Users/myusername __CF_USER_TEXT_ENCODING == 0x1F5:0:0 HOME == /Users/myusername SECURITYSESSIONID == 23bac080 SHELL == /bin/bash ----- Output of this script with BBEDit's "Run In Terminal": ----- LOGNAME == myusername HOST == jh.my.work GROUP == myusername SHLVL == 2 PATH == /bin:/sbin:/usr/bin:/usr/sbin:/opt/local/bin HTTP_PROXY == http://my.work.proxy:8080/ USER == myusername HOSTTYPE == powermac VENDOR == apple HOME == /Users/myusername TERM_PROGRAM_VERSION == 100.1.8 TERM_PROGRAM == Apple_Terminal SHELL == /bin/bash SECURITYSESSIONID == 23bac080 __CF_USER_TEXT_ENCODING == 0x1F5:0:0 _ == /usr/bin/perl TERM == xterm-color MACHTYPE == powerpc PWD == /private/tmp/501/Cleanup At Startup OSTYPE == darwin ----- output when run as cron script: ----- SHLVL == 1 SHELL == /bin/sh HOME == /Users/myusername PATH == /usr/bin:/bin _ == /usr/bin/perl LOGNAME == myusername PWD == /Users/myusername USER == myusername ----- But Cronnix also has a "run now" option to test ones scripts, and when I use that, I get the same output as when it's run in the Terminal. Can you see now why I was a little confused? Not to mention my Linux colleague's advice that the environment variable for my favourite shell would be some kind of global variable. Off I go to investigate the $HOME/.MacOSX/environment.plist idea... At 12:49 +1000 8/1/05, John Horner wrote, in part: >Output of this script with BBEDit's "Run In Terminal": >----- [quoted text clipped - 3 lines] >SHLVL == 2 >PWD == /private/tmp/501/Cleanup At Startup Note the SHLVL which is incremented each time a shell invokes another shell. BBEdit has been known to make a copy of a "script" in /tmp/ which it passes to Terminal, or something else, for execution. There may be an added shebang line at the front. In fact there needs to be because your script is obviously perl. Note the PWD variable; look there for such a file. In AppleScript after 10.3 the do shell script command always takes one to "sh". A shebang line at the start of the script to be "done" can point to bash or tcsh but the SHLVL will get increased as a daughter process is started up by sh. Note that /usr/bin/sh is a copy of /usr/bin/bash and not, as is common in the Linux world, a hard link to bash. In compatibility mode - sh - bash does not do all of the fancy things it does when called as bash. A similar arrangement holds for csh and tcsh. >PATH == /bin:/sbin:/usr/bin:/usr/sbin:/opt/local/bin It is curious that PATH contains /opt/local/bin. I don't think OS neXt ever does that by itself. Darwin Ports and Fink might create such things but, of course, you or your employer can do it too. Are you involved with Apple's X11? Do experiment with BBEdit worksheets. They will provide yet another option for running the script - just select and enter. Signature--> Life begins at ovulation. Ladies should endeavor to get every young life fertilized. <-- |
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