bash: checking if an env var is set?

[Angel Tsankov]

How do I check if an environment variable is set?

[Chris]

Angel Tsankov wrote:

[ follow-up set to c.o.l.misc as my nntp doesn't carry c.o.l.help ]

Post by Angel Tsankov
How do I check if an environment variable is set?

Use echo. e.g.

echo $PATH

[Bit Twister]

Post by Angel Tsankov
How do I check if an environment variable is set?

Well doing a
man test
would suggest you can test string for nonzero length or if length is zero.

[Daniel Ganek]

Post by Angel Tsankov
How do I check if an environment variable is set?

${foo+1}

If $foo is unset this expands to NULL
If $foo is set (including set to NULL) this will expand to 1

If NULL and unset are equivalent use ${foo:+1}

/dan

[CBFalconer]

Post by Angel Tsankov
How do I check if an environment variable is set?

If programatically, use getenv() in C. It returns NULL if not
found. From N869 (C standard):

7.20.4.5 The getenv function

Synopsis

[#1]

#include <stdlib.h>
char *getenv(const char *name);

Description

[#2] The getenv function searches an environment list,
provided by the host environment, for a string that matches
the string pointed to by name. The set of environment names
and the method for altering the environment list are
implementation-defined.

[#3] The implementation shall behave as if no library
function calls the getenv function.

Returns

[#4] The getenv function returns a pointer to a string
associated with the matched list member. The string pointed
to shall not be modified by the program, but may be
overwritten by a subsequent call to the getenv function. If
the specified name cannot be found, a null pointer is
returned.

[Chris F.A. Johnson]

Post by Angel Tsankov
How do I check if an environment variable is set?

[ -n "${VAR+x}" ] ## Fails if VAR is unset

[ -n "${VAR:+x}" ] ## Fails if VAR is unset or empty

[ -n "${VAR-x}" ] ## Succeeds if VAR is unset

[ -n "${VAR:-x}" ] ## Succeeds if VAR is unset or empty

[Feranija]

Post by Angel Tsankov
How do I check if an environment variable is set?

echo $VARIABLE

[Some Dude]

Post by Angel Tsankov
How do I check if an environment variable is set?

shell:~$ env

That will list the environment variables.