Just like how you learn any other programming language: use it to solve your problems.
Anyway, here's a few steps that I would recommend:
1. Go through http://tldp.org/LDP/abs/html/ and http://www.tldp.org/LDP/Bash-Beginners-Guide/html/ , or at least go through the table of contents so that you have a feeling of what bash is capable of. A few important things are: if, while, for, switch, functions, string manipulation, pipe, subshell, command substitution
2. Understand the execution model. Variables in subshell cannot be accessed from the parent shell, this is a common mistake
3. Learn to avoid common pitfalls. I always recommend my colleagues to always quote the variables in double quote, always use "$@" instead of "$*", always use double square bracket instead of single square bracket for testing, use echo to pass return value from functions instead of assigning to global variable
4. Learn awk, sed, grep. Bash can be quite limiting when it comes to data processing and these tools can be quite powerful. You can use bash to glue different filters together at a higher level.
Bash is a fantastic language and there are quite a lot of things that can be much more quickly in bash than in other "proper" languages. A lot of people says that it's too difficult to maintain a shell script beyond a "critical mass" but I believe that if you follow good practices and write modular codes, shell scripts can be very manageable.
Anyway, here's a few steps that I would recommend:
1. Go through http://tldp.org/LDP/abs/html/ and http://www.tldp.org/LDP/Bash-Beginners-Guide/html/ , or at least go through the table of contents so that you have a feeling of what bash is capable of. A few important things are: if, while, for, switch, functions, string manipulation, pipe, subshell, command substitution
2. Understand the execution model. Variables in subshell cannot be accessed from the parent shell, this is a common mistake
3. Learn to avoid common pitfalls. I always recommend my colleagues to always quote the variables in double quote, always use "$@" instead of "$*", always use double square bracket instead of single square bracket for testing, use echo to pass return value from functions instead of assigning to global variable
4. Learn awk, sed, grep. Bash can be quite limiting when it comes to data processing and these tools can be quite powerful. You can use bash to glue different filters together at a higher level.
Bash is a fantastic language and there are quite a lot of things that can be much more quickly in bash than in other "proper" languages. A lot of people says that it's too difficult to maintain a shell script beyond a "critical mass" but I believe that if you follow good practices and write modular codes, shell scripts can be very manageable.