[SOLVED] aliases and bash scripts

dedec0 · 08-05-2015, 07:36 PM

I have been fiddling around a bit for something I tried to use many times, and it never worked (I manually expanded the aliases, where I used them). Today there was a more tries, but still nothing so clear for the problem.

Basic idea: want to use my alias on my shell scripts.

Here is some output that might be a more informative example than long paragraphs:

Code:

$ cat ~/.bashrc
# ...
# ONLY some aliases [trimmed from this output]
# ...
alias dddttt='"date" "+%F %T"'

# If not running interactively, don't do anything
[ -z "$PS1" ] && return
# (above: infamous line I took long to read about or to note it)

# ...
# more aliases, functions and so on
# ...

$ cat ~/bomb.sh
#!/bin/bash
# date "+%F %T"
dddttt

$ bash
$ ~/bomb.sh
/home/user/bomb.sh: line 3: dddttt: command not found

So, why it still don't work?? I have moved my aliases above that "infamous" line. It makes sense to work. Doesn't it!?

dedec0 · 08-05-2015, 07:42 PM

Some of you may find this page useful. For me, it is kind of confuse, mostly - although it showed me the "infamous line".

Some people around here you might use/understand it better than myself:

http://xpt.sourceforge.net/techdocs/...h/ar01s13.html

ljb643 · 08-05-2015, 07:44 PM

Because Bash does not expand aliases unless the shell is interactive (by default). Can you imagine what could happen if scripts had the commands they were expecting to run changed by aliases? There is an option to override this, but you would probably be better off not using aliases in shell scripts.

dedec0 · 08-06-2015, 09:29 AM

But I would really like to use my aliases in my shell scripts. Some of them are more complex and big than what I've given here as an example. Maybe I'll even turn on my functions too, since they should not conflict with any program name, installed or not.

Is the option shopt -e expand_aliases ? Can I put it inside my scripts? Or just in bashrc (which is not that good) ?

rtmistler · 08-06-2015, 09:39 AM

Quote:

Originally Posted by dedec0

But I would really like to use my aliases in my shell scripts. Some of them are more complex and big than what I've given here as an example. Maybe I'll even turn on my functions too, since they should not conflict with any program name, installed or not.

Is the option shopt -e expand_aliases ? Can I put it inside my scripts? Or just in bashrc (which is not that good) ?

For me mainly aliases are there to either simplify typing, or put in stuff which I'd normally not think to add, such as the --color for the ls command.

Variables in bash defined in the script are there for the duration of the script. So if you say something like:

Code:

#!/bin/sh
# This is my script

LS='/bin/ls --color=auto'

And then you use $LS within your script, you are thus using an alias.

dedec0 · 08-06-2015, 11:35 AM

I knew I can use variables to execute anything. But I want to use the already defined aliases in my scripts - so they're much easier to write and to also understand them, for whoever reads it. The useful aliases are in bashrc, so they will be defined there, and not in the script itself, like that $LS.

Anyway, later today I'll try something I have just found:

http://www.tldp.org/LDP/abs/html/aliases.html

Code:

#!/bin/bash
# alias.sh

# Must set this option, else script will not expand aliases.
shopt -s expand_aliases

alias Jesse_James='echo "\"Alias Jesse James\" was a 1959 comedy starring Bob Hope."'
Jesse_James

echo; echo; echo;

# [...]

rtmistler · 08-06-2015, 12:54 PM

Quote:

Originally Posted by dedec0

I knew I can use variables to execute anything. But I want to use the already defined aliases in my scripts - so they're much easier to write and to also understand them, for whoever reads it. The useful aliases are in bashrc, so they will be defined there, and not in the script itself, like that $LS.

Anyway, later today I'll try something I have just found:

http://www.tldp.org/LDP/abs/html/aliases.html

Code:

#!/bin/bash
# alias.sh

# Must set this option, else script will not expand aliases.
shopt -s expand_aliases

alias Jesse_James='echo "\"Alias Jesse James\" was a 1959 comedy starring Bob Hope."'
Jesse_James

echo; echo; echo;

# [...]

I don't think that's a good idea. You write something using particular definitions only known to your login and then distribute it to other people, there may be problems with privileges, as well as future problems when you change things.

Making it easier is not about dumbing it down, but instead providing good structure, comments, and educating the audience if they still can't follow your code.

ondoho · 08-06-2015, 06:17 PM

Quote:

Originally Posted by dedec0

http://www.tldp.org/LDP/abs/html/aliases.html

it says so right there:

Quote:

Originally Posted by tldp

In a script, aliases have very limited usefulness. (...) Bash does not expand arguments within the alias body. Moreover, a script fails to expand an alias itself within "compound constructs," such as if/then statements, loops, and functions. An added limitation is that an alias will not expand recursively. Almost invariably, whatever we would like an alias to do could be accomplished much more effectively with a function.

but i think i already know what you're going to say to that:

"But I really, really want to use aliases in my scripts..."

well, why not, go ahead.

dedec0 · 08-08-2015, 04:43 PM

That's bad. I didn't read all that document... (just tired).

Script to convert all aliases to functions, activate!

LOL