6 янв. 2010 г. · To get the assigned value, or default if it's missing: FOO="${VARIABLE:-default}" # FOO will be assigned 'default' value if VARIABLE not set or ...

30 авг. 2010 г. · The right way: if [ -z ${var+x} ]; then echo "var is unset"; else echo "var is set to '$var'"; fi where ${var+x} is a parameter expansion which evaluates to

6 февр. 2023 г. · I wrote a bash script to set the environment variable VAR if it is currently not set: example.sh #!/bin/bash if [ -z $VAR ]; then export VAR=abc fi

11 окт. 2016 г. · The problem is not in the default, but in echo : -n has a special meaning for it (check help echo ). Use printf instead:

6 авг. 2016 г. · The first $(something) may return an empty string, however the conditional assignment ?= works only if the previous variable is not set, not if empty.

2 сент. 2016 г. · Most compact way is : ${MY_VARIABLE:?} It will print a message and return with non-0 code if it doesn't exist: -bash: MY_VARIABLE: parameter null or not set.

1 июн. 2012 г. · In a given shell, normally I'd set a variable or variables and then run a command. Recently I learned about the concept of prepending a variable definition to ...

20 апр. 2016 г. · You can use parameter expansion like this: foo=${foo:-default value} This will set $foo to "default value" if it is not defined or empty.

30 нояб. 2018 г. · You can check the exit status of your last command executed with $? In shell and see if it holds 0 for success or 1 for failure.

27 нояб. 2018 г. · How do set a variable value to something based on an environment variable is set. For example, I want it to be var1 = var2 if ENV_VARIABLE==true else var3.