system calls and shell aliases

Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:

Replies are listed 'Best First'.
Re: system calls and shell aliases by Fletch (Bishop) on Aug 17, 2005 at 03:51 UTC
Of course what no one's mentioned yet is that this particular alias (changing the working directory) isn't really going to do much good since you're changing the child shell's CWD, not your perl process'. See the FAQ (`perldoc -q environment`). -- We're looking for people in ATL	[reply] [d/l]
Re: system calls and shell aliases by davidrw (Prior) on Aug 17, 2005 at 03:05 UTC
When the `system` or `exec` or backticks spawn a shell it doesn't load your settings, and doesn't inherit the current environment. As a workaround, you could just run "cd $dirname && pwd" as the command instead of "tt". Alternatively (and more robustly), move your "tt" from being an alias to being an executable shell script in say ~/bin/tt .. then your system or backtick call can just run "/home/myname/bin/tt".	[reply] [d/l] [select]
Re: system calls and shell aliases by merlyn (Sage) on Aug 17, 2005 at 03:06 UTC
Perhaps you're missing that system/exec/backquotes always use /bin/sh, which normally don't have aliases? -- Randal L. Schwartz, Perl hacker Be sure to read my standard disclaimer if this is a reply.	[reply]
Re: system calls and shell aliases by superfrink (Curate) on Aug 17, 2005 at 05:21 UTC
A shell `alias` is something that your shell deals with. The aliases only exist as shortcuts in your shell white the shell is executing. These aliases do not exist as program files in the filesystem. When you run `system("tt")` from perl the directories in your `PATH` environment variable are searched for a program file named `tt`. In this case no program named `tt` is being found. The man page for BASH indicates alias expansion takes place after one full line of text is read in. This could mean that aliases are only expanded when BASH is reading from a terminal and not when it has been passed a command to run. Normally BASH runs in a terminal and executes a loop where it reads a command and runs the command then repeats. It might be that aliases are only expaned inside of that loop but I'm not sure that is the case. I tried running `perl -e 'system("bash --login -c l");'` where I have a BASH alias mapping "l" to "ls -l" and I got back: "`bash: line 1: l: command not found`". As an aside the man page for BASH has this text in the BUGS section: `Aliases are confusing in some uses.`	[reply] [d/l] [select]
Re: system calls and shell aliases by Anonymous Monk on Aug 17, 2005 at 12:24 UTC
Whaow, Thank you guys for the quick response. The tt was only an dirty instance I used for exemplification. In reality, I am supposed to write a script to run as a cron for an integrated library system. This system runs a number of interactive aliases. I was hoping to use the shortcut of just running the aliases. The ideas of creating executable shell scripts sounds like an excellent idea. Thank you so much guys. Randal, it's an honor! Alia(s)mused..	[reply]
Re^2: system calls and shell aliases by Anonymous Monk on Jun 14, 2015 at 10:11 UTC
why not sourcing your .bashrc (or anywhere you define your alias) before calling the alias? `perl -e 'system("source ~/.profile; source ~/.bashrc; bash --login -c +l");'` [download] For instance, matlab is an alias for me defined in ~/.profile. Try to check if matlab exist as a command from perl: `$perl -e 'system("command -v matlab")' $perl -e 'system("source ~/.profile;command -v matlab")' alias matlab='/Applications/MATLAB_R2015a.app/bin/matlab'` [download] Best, Hatef	[reply] [d/l] [select]