Bash Script – Echo Env Variables Starting with nlu_setting

bashenvironment-variablesshellvariable

I am looking for a way to echo names and values of all env variables that start with nlu_setting, so the output might look like:

nlu_setting_json=true
nlu_setting_global=0
nlu_setting_bar=foo

does anyone know how to do this?

Best Answer

for var in "${!nlu_setting_@}"; do
    printf '%s=%s\n' "$var" "${!var}"
done

The expansion ${!nlu_setting_@} is a bash-specific expansion that returns a list of variable names matching a particular prefix. Here we use it to ask for all names that start with the string nlu_setting_. We loop over these names and output the name along with the value of that variable.

We get the value of the variable using variable indirection (${!var}).

Related Solutions

Unset all ENV variables matching _PROXY

That's because unset is a shell builtin and not an external command. This means that xargs can't use it since that only runs commands that are in your $PATH. You'd get the same problem if you tried with cd:

$ ls -l
total 4
drwxr-xr-x 2 terdon terdon 4096 Jun 16 02:02 foo
$ echo foo | xargs cd
xargs: cd: No such file or directory

One way around this is to use a shell loop which, since it is part of the shell, will be able to run shell builtins. I also simplified your command a bit, there's no need for column, you can set the field separator for awk and there's no need for a second grep, just tell awk to print lines that don't match no_proxy:

while read var; do unset $var; done < <(env | grep -i proxy | 
    awk -F= '!/no_proxy/{print $1}')

Bash – Use env with environment variables from file

This is an example of not using the right tool for the job. env isn't the only tool that sets environment variables and then chain loads another program. And it doesn't read variable data from file.

Of course, the . a.k.a. source command is not the right tool for this job, either.

It permits the file to unexpectedly contain shell commands other than simple variable assignments, which in certain circumstances (depending from what the configuration file is) can be a massive security hole.
A series of assignments as in the example in the question, sourced by ., sets shell variables, not environment variables. They aren't automatically exported.

The right tools are ordinary chain-loading tools from several toolsets of such tools.

One such is read-conf from the nosh toolset, designed to read exactly this kind of configuration file (such as /etc/rc.conf from — say — PC-BSD) and set environment variables without implementing and opening up configuration data files to an entire shell language syntax:

jdebp % uname
Linux
jdebp % cat e
a=3
b="5 6"
jdebp % read-conf e printenv | tail -n 3
USER=jdebp
a=3
b=5 6
jdebp %

jdebp % uname
FreeBSD
jdebp % read-conf /etc/rc.conf printenv | head -n 2
cron_enable=NO
sendmail_msp_queue_enable=NO
jdebp %

Another such tool is Wayne Marshall's runenv from perp.

Best Answer

Related Solutions

Unset all ENV variables matching _PROXY

Bash – Use env with environment variables from file

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