When you are typing commands into a shell (such as bash), the shell expands aliases that you have defined (such as ll in your example). Those aliases are not expanded when your shell is executing commands contained in a file (i.e., a shell script).

Some utilities look at variables defined in their environment and if specific variables are found, those utilities behave differently. The environment variable affects they way those utility behave no matter how that utility was invoked (both by typing the utility name into the shell and by finding a request to run it from a shell script). When export LESS=-N is in the environment of your shell on OS X and you invoke the less utility, the output produced by less will include line numbers in the output.

For example, if you type in the commands:

Code:

unset LESS
man less|less

you will see the man page for the less utility. But, if you type in the command:

Code:

export LESS="-N"

and later type in the command:

Code:

man less|less

you will see the man page for the less utility with each line preceded by its line number.

I personally believe that the LESS environment variable (and similar environment variables designed to alter the behavior of a commonly used utilities) is dangerous because some shell scripts depend on normal less output and if they invoke less not knowing that LESS has been set, the output they see may be misinterpreted.

But there are some environment variables that are expected to be set to get proper operation from lots of utilities. These include, but are not limited to:Run the env command to see what is currently set in your environment.

Note that if PAGER is set to less in your environment and you have set LESS in your environment to -N, the output from the man command will include line numbers (and it may make reading the man pages harder since they were formatted assuming that line numbers would not be included when they were displayed). Note that environment variable names (and utility names and option names and most other strings used in shell commands and scripts are case sensitive).