Get list of variables whose name matches a certain pattern - bash

Question

In bash
echo ${!X*}
will print all the names of the variables whose name starts with 'X'.
Is it possible to get the same with an arbitrary pattern, e.g. get all the names of the variables whose name contains an 'X' in any position?

Answer 1

Use the builtin command compgen:
compgen -A variable | grep X

Answer 2

This should do it:
env | grep ".*X.*"
Edit: sorry, that looks for X in the value too.
This version only looks for X in the var name
env | awk -F "=" '{print $1}' | grep ".*X.*"
As Paul points out in the comments, if you're looking for local variables too, env needs to be replaced with set:
set | awk -F "=" '{print $1}' | grep ".*X.*"

Answer 3

Easiest might be to do a
printenv |grep D.*=
The only difference is it also prints out the variable's values.

Answer 4

This will search for X only in variable names and output only matching variable names:
set | grep -oP '^\w*X\w*(?==)'
or for easier editing of searched pattern
set | grep -oP '^\w*(?==)' | grep X
or simply (maybe more easy to remember)
set | cut -d= -f1 | grep X
If you want to match X inside variable names, but output in name=value form, then:
set | grep -P '^\w*X\w*(?==)'
and if you want to match X inside variable names, but output only value, then:
set | grep -P '^\w*X\w*(?==)' | grep -oP '(?<==).*'

Answer 5

Enhancing Johannes Schaub - litb answer removing fork/exec in modern bash we could do
compgen -A variable -X '!*X*'
i.e an X in any position in the variable list.

Answer 6

env | awk -F= '{if($1 ~ /X/) print $1}'

Answer 7

To improve on Johannes Schaub - litb's answer:
There is a shortcut for -A variable and a flag to include a pattern:
compgen -v -X '!*SEARCHED*'
-v is a shortcut for -A variable
-X takes a pattern that must not be matched.
Hence -v -X '!*SEARCHED*' reads as:
variables that do not, not match "anything + SEARCHED + anything"
Which is equivalent to:
variables that do match "anything + SEARCHED + anything"
The question explicitly mentions "variables" but I think it's safe to say that many people will be looking for "custom declared things" instead.
But neither functions nor aliases are listed by -v.
If you are looking for variables, functions and aliases, you should use the following instead:
compgen -av -A function -X '!*SEARCHED*'
# equivalent to:
compgen -A alias -A variable -A function -X '!*SEARCHED*'
And if you only search for things that start with a PREFIX, compgen does that for you by default:
compgen -v PREFIX
You may of course adjust the options as needed, and the official doc will help you: https://www.gnu.org/software/bash/manual/html_node/Programmable-Completion-Builtins.html

Answer 8

to expand Phi's and Johannes Schaub - litb's answers for the following use case:
print contents of all environment variables whose names match a pattern as strings which can be reused in other (Bash) scripts, i.e. with all special characters properly escaped and the whole contents quoted
In case you have the following environment variables
export VAR_WITH_QUOTES=\"FirstName\ LastName\"\ \<firstname.lastname#example.com\>
export VAR_WITH_WHITESPACES="
a bc
"
export VAR_EMPTY=""
export VAR_WITH_QUOTES_2=\"\'
then the following snippet prints all VAR* environment variables in reusable presentation:
for var in $(compgen -A export -X '!VAR*'); do
printf "%s=%s\n" "$var" "${!var#Q}"
done
Snippet is is valid for Bash 4+.
The output is as follows, please note output for newlines, empty variables and variables which contain quotation characters:
VAR_EMPTY=''
VAR_WITH_QUOTES='"FirstName LastName" <firstname.lastname#example.com>'
VAR_WITH_QUOTES_2='"'\'''
VAR_WITH_WHITESPACES=$' \n\ta bc\n'
This also relates to the question Escape a variable for use as content of another script