view my lowercase shell variables from a bash function using awk

Question

Outcome

Filter output the variables displayed using set or declare to show only lowercase named shell variables which is the convention I use for setting shell variables while testing.

Example

I set these:

$ declare -A pid=()
$ a=DHCP
$ something=test

I want the output to look like this:

$ lvar
a=DHCP
pids=()
something=test

I came up with this awk command for the lvar function:

declare | awk -F'=' '$1 ~ /^[a-z]+$/'

This works perfectly when run from the command line. However, as a function sourced in and run, I get an error which I think is caused by awk's field parameter $1 being interpreted as a bash function parameter.

$ vi func
function lvar() {
  declare |awk -F'=' '$1 ~ /^[a-z]+$/'
}

Running lvar gives this error:

$ lvar
awk: cmd. line:1:  ~ /^[a-z]+$/
awk: cmd. line:1:  ^ syntax error

What am I doing wrong here?

$ declare -p -f lvar
lvar () 
{ 
    declare | awk -F'=' '$1 ~ /^[a-z]+$/'
}

Update 1

My original approach with an awk command defined as a bash function, does actually work - only on my Linux box and not on my Mac where I originally defined it.

I'll have to figure out the macOS issue and post an update to you all here in due course.
Many thanks for your time :)

Update 2

Okay, I checked if the bash shopt options on my Linux vs macOS were different but that wasn't it.

I opened iTerm on Mac and the function behaves as expected but shows no output in Terminal.app.

Very odd that its specific to some setting in Terminal.app. I'm at a loss.

Answer 1

With bash, you can get the list of variable names (though not the ones that have been declared but not assigned) into an array with:

readarray -t Vars < <(compgen -v)

You can filter that with grep:

readarray -t Vars < <(compgen -v | grep -x '[[:lower:]]*') &&
  [ "${#Vars[@]}" -gt 0 ] &&
  declare -p -- "${Vars[@]}"

For the all-lowercase ones for instance.

Change the grep filter to grep -v '[[:upper:]]' for all variables except those whose name contains an uppercase letter, or grep '[[:lower:]]' | grep -v '[[:upper:]]' for those with at least one lowercase letter and no upper.

In any case, you can't post-process the output of declare line-by-line like you're trying to do as variable values may very well be made of several lines, and at least when the posix option is enabled, bash will display them (the scalar ones at least) like:

var='line 1
line 2'

With the posix option disabled, it seems that bash 5.1 at least always renders the newline character as $'\n' which would guarantee that each variable definition is on a single line.

In that case, you could do:

(set +o posix; declare | grep -E '^[[:lower:]]+=')

To list the definition of variables whose name is all-lowercase (assuming the variable values are short enough or that your grep doesn't choke on lines larger than LINE_MAX bytes).

Like for compgen -v, that doesn't include declared unassigned variables.

Answer 2

With zsh:

set -o extendedglob
typeset -m '[[:lower:]]#'

Would print the definition of variables whose name is made entirely of lowercase letters.

set -o extendedglob
typeset -m '^*[[:upper:]]*'

For those that don't contain uppercase letters, to also include foo_bar or var1 for instance or

set -o extendedglob
typeset -m '*[[:lower:]]*~*[[:upper:]]*'

For those that contain at least one lowercase letter, and no upper case ones, to exclude variables named like __ or _123_ or those with letters that don't have a lowercase nor uppercase form compared to the previous one.

Beware zsh completion defines a lot of such variables.

Answer 3

Okay, my function method stands. There was some crazy Terminal.app issue which had nothing to do with the function.

From:

$ vi ~/.bash_functions
lvar() {
  declare |awk -F'=' '$1 ~ /^[a-z]+$/'
}

To:

$ vi ~/.bash_functions
function lvar() {
  declare |awk -F'=' '$1 ~ /^[a-z]+$/'
}

I really wish I could point a finger as to what the problem was but it started working in Terminal.app after I gave the long function definition format using function keyword, in my main bash functions file, closed Terminal.app and reopened it. Hey presto - it worked! Then removed the 'function' keyword in my main bash functions and it kept on working. - Scratching my head. Apologies if this wasted anyone's time.