Why doesn't my Bash script recognize aliases?

Question

In my ~/.bashrc file reside two definitions:

1. commandA, which is an alias to a longer path
2. commandB, which is an alias to a Bash script

I want to process the same file with these two commands, so I wrote the following Bash script:

---

#!/bin/bash

for file in $@
    do
    commandA $file
    commandB $file
done

Even after logging out of my session and logging back in, Bash prompts me with command not found errors for both commands when I run this script.

What am I doing wrong?

Answer 1

First of all, as ddeimeke said, aliases by default are not expanded in non-interactive shells.

Second, .bashrc is not read by non-interactive shells unless you set the BASH_ENV environment variable.

But most importantly: don't do that! Please? One day you will move that script somewhere where the necessary aliases are not set and it will break again.

Instead set and use environment variables as shortcuts in your script:

#!/bin/bash

CMDA=/path/to/gizmo
CMDB=/path/to/huzzah.sh

for file in "$@"
    do
    "$CMDA" "$file"
    "$CMDB" "$file"
done

Answer 2

Aliases can't be exported so they're not available in shell scripts in which they aren't defined. In other words, if you define them in ~/.bashrc they're not available to your_script.sh (unless you source ~/.bashrc in the script, which I wouldn't recommend but there are ways to do this properly).

However, functions can be exported and would be available to shell scripts that are run from an environment in which they are defined. This can by placing this in your bashrc:

foo()
{
    echo "Hello World!"
}
export -f foo

As the Bash manual says, "For almost every purpose, shell functions are preferred over aliases."

Answer 3

If you look into the bash manpage you find:

Aliases are not expanded when the shell is not interactive, unless the expand_aliases shell option is set using shopt (see the description of shopt under SHELL BUILTIN COMMANDS below).

So put a

shopt -s expand_aliases

in your script.

Answer 4

When you run your script, a new instance of bash is run. This instance is not interactive and therefore does not read your .bashrc file.

A simpler way to do what you want can be simply to force reading the the .bashrc file by using source. Add the following line at the beginning of your script:

#!/bin/bash

# Add the following line to your script. 
source ~/.bashrc

for file in $@
    do
    $CMDA $file
    $CMDB $file
done