This question already has answers here:
Assign results of globbing to a variable in Bash
(4 answers)
Closed 7 years ago.
Please, don't take this the wrong way, but before someone answers and tells me I should use an array, I'm looking for the reason why the following code doesn't work, not 'how to do it correctly'.
I've searched the internet for the reason for this.
Given in bash:
function fn1 {
file=$HOME/$1*.cfg
echo $file
}
touch $HOME/abc-def.cfg
fn1 abc
returns /home/user/abc*.cfg
Why doesn't the * expand to give /home/user/abc-def.cfg?
A workaround:
file=$HOME/$(ls -1 $HOME|grep $1)
is not elegant.
Background: I know there will be only one file that begins 'abc', but the rest of the filename can vary, I don't care about that, just the initial identifier (abc in the case above).
Lastly, great forum, use it a lot, but this is the first time I didn't find an answer, so my first posting - be kind :-)
Works for me.
$ function fn1 {
> file=$HOME/$1*.cfg
> echo $file
> }
$
$ touch $HOME/abc-def.cfg
$ fn1 abc
/home/jackman/abc-def.cfg
However, if I disable filename expansion, I see your results:
$ set -f
$ fn1 abc
/home/jackman/abc*.cfg
Have you done set -f beforehand? If you want to account for that in your function:
function fn1 {
local filename_expansion_disabled
[[ $- == *f* ]]; filename_expansion_disabled=$?
local file=$HOME/"$1"*.cfg
[[ $filename_expansion_disabled -eq 0 ]] && set +f
echo $file
[[ $filename_expansion_disabled -eq 0 ]] && set -f || true
}
Then
$ set +f
$ fn1 abc
/home/jackman/abc-def.cfg
$ set -f
$ fn1 abc
/home/jackman/abc-def.cfg
Running the function in a subshell has the same effect, and is simpler at the expense of an insignificant performance penalty:
fn1() (
file=$HOME/"$1"*.cfg
set +f
echo $file
)
Related
I've got a few Unix shell scripts where I need to check that certain environment variables are set before I start doing stuff, so I do this sort of thing:
if [ -z "$STATE" ]; then
echo "Need to set STATE"
exit 1
fi
if [ -z "$DEST" ]; then
echo "Need to set DEST"
exit 1
fi
which is a lot of typing. Is there a more elegant idiom for checking that a set of environment variables is set?
EDIT: I should mention that these variables have no meaningful default value - the script should error out if any are unset.
Parameter Expansion
The obvious answer is to use one of the special forms of parameter expansion:
: ${STATE?"Need to set STATE"}
: ${DEST:?"Need to set DEST non-empty"}
Or, better (see section on 'Position of double quotes' below):
: "${STATE?Need to set STATE}"
: "${DEST:?Need to set DEST non-empty}"
The first variant (using just ?) requires STATE to be set, but STATE="" (an empty string) is OK — not exactly what you want, but the alternative and older notation.
The second variant (using :?) requires DEST to be set and non-empty.
If you supply no message, the shell provides a default message.
The ${var?} construct is portable back to Version 7 UNIX and the Bourne Shell (1978 or thereabouts). The ${var:?} construct is slightly more recent: I think it was in System III UNIX circa 1981, but it may have been in PWB UNIX before that. It is therefore in the Korn Shell, and in the POSIX shells, including specifically Bash.
It is usually documented in the shell's man page in a section called Parameter Expansion. For example, the bash manual says:
${parameter:?word}
Display Error if Null or Unset. If parameter is null or unset, the expansion of word (or a message to that effect if word is not present) is written to the standard error and the shell, if it is not interactive, exits. Otherwise, the value of parameter is substituted.
The Colon Command
I should probably add that the colon command simply has its arguments evaluated and then succeeds. It is the original shell comment notation (before '#' to end of line). For a long time, Bourne shell scripts had a colon as the first character. The C Shell would read a script and use the first character to determine whether it was for the C Shell (a '#' hash) or the Bourne shell (a ':' colon). Then the kernel got in on the act and added support for '#!/path/to/program' and the Bourne shell got '#' comments, and the colon convention went by the wayside. But if you come across a script that starts with a colon, now you will know why.
Position of double quotes
blong asked in a comment:
Any thoughts on this discussion? https://github.com/koalaman/shellcheck/issues/380#issuecomment-145872749
The gist of the discussion is:
… However, when I shellcheck it (with version 0.4.1), I get this message:
In script.sh line 13:
: ${FOO:?"The environment variable 'FOO' must be set and non-empty"}
^-- SC2086: Double quote to prevent globbing and word splitting.
Any advice on what I should do in this case?
The short answer is "do as shellcheck suggests":
: "${STATE?Need to set STATE}"
: "${DEST:?Need to set DEST non-empty}"
To illustrate why, study the following. Note that the : command doesn't echo its arguments (but the shell does evaluate the arguments). We want to see the arguments, so the code below uses printf "%s\n" in place of :.
$ mkdir junk
$ cd junk
$ > abc
$ > def
$ > ghi
$
$ x="*"
$ printf "%s\n" ${x:?You must set x} # Careless; not recommended
abc
def
ghi
$ unset x
$ printf "%s\n" ${x:?You must set x} # Careless; not recommended
bash: x: You must set x
$ printf "%s\n" "${x:?You must set x}" # Careful: should be used
bash: x: You must set x
$ x="*"
$ printf "%s\n" "${x:?You must set x}" # Careful: should be used
*
$ printf "%s\n" ${x:?"You must set x"} # Not quite careful enough
abc
def
ghi
$ x=
$ printf "%s\n" ${x:?"You must set x"} # Not quite careful enough
bash: x: You must set x
$ unset x
$ printf "%s\n" ${x:?"You must set x"} # Not quite careful enough
bash: x: You must set x
$
Note how the value in $x is expanded to first * and then a list of file names when the overall expression is not in double quotes. This is what shellcheck is recommending should be fixed. I have not verified that it doesn't object to the form where the expression is enclosed in double quotes, but it is a reasonable assumption that it would be OK.
Try this:
[ -z "$STATE" ] && echo "Need to set STATE" && exit 1;
Your question is dependent on the shell that you are using.
Bourne shell leaves very little in the way of what you're after.
BUT...
It does work, just about everywhere.
Just try and stay away from csh. It was good for the bells and whistles it added, compared the Bourne shell, but it is really creaking now. If you don't believe me, just try and separate out STDERR in csh! (-:
There are two possibilities here. The example above, namely using:
${MyVariable:=SomeDefault}
for the first time you need to refer to $MyVariable. This takes the env. var MyVariable and, if it is currently not set, assigns the value of SomeDefault to the variable for later use.
You also have the possibility of:
${MyVariable:-SomeDefault}
which just substitutes SomeDefault for the variable where you are using this construct. It doesn't assign the value SomeDefault to the variable, and the value of MyVariable will still be null after this statement is encountered.
Surely the simplest approach is to add the -u switch to the shebang (the line at the top of your script), assuming you’re using bash:
#!/bin/sh -u
This will cause the script to exit if any unbound variables lurk within.
${MyVariable:=SomeDefault}
If MyVariable is set and not null, it will reset the variable value (= nothing happens).
Else, MyVariable is set to SomeDefault.
The above will attempt to execute ${MyVariable}, so if you just want to set the variable do:
MyVariable=${MyVariable:=SomeDefault}
In my opinion the simplest and most compatible check for #!/bin/sh is:
if [ "$MYVAR" = "" ]
then
echo "Does not exist"
else
echo "Exists"
fi
Again, this is for /bin/sh and is compatible also on old Solaris systems.
bash 4.2 introduced the -v operator which tests if a name is set to any value, even the empty string.
$ unset a
$ b=
$ c=
$ [[ -v a ]] && echo "a is set"
$ [[ -v b ]] && echo "b is set"
b is set
$ [[ -v c ]] && echo "c is set"
c is set
I always used:
if [ "x$STATE" == "x" ]; then echo "Need to set State"; exit 1; fi
Not that much more concise, I'm afraid.
Under CSH you have $?STATE.
For future people like me, I wanted to go a step forward and parameterize the var name, so I can loop over a variable sized list of variable names:
#!/bin/bash
declare -a vars=(NAME GITLAB_URL GITLAB_TOKEN)
for var_name in "${vars[#]}"
do
if [ -z "$(eval "echo \$$var_name")" ]; then
echo "Missing environment variable $var_name"
exit 1
fi
done
We can write a nice assertion to check a bunch of variables all at once:
#
# assert if variables are set (to a non-empty string)
# if any variable is not set, exit 1 (when -f option is set) or return 1 otherwise
#
# Usage: assert_var_not_null [-f] variable ...
#
function assert_var_not_null() {
local fatal var num_null=0
[[ "$1" = "-f" ]] && { shift; fatal=1; }
for var in "$#"; do
[[ -z "${!var}" ]] &&
printf '%s\n' "Variable '$var' not set" >&2 &&
((num_null++))
done
if ((num_null > 0)); then
[[ "$fatal" ]] && exit 1
return 1
fi
return 0
}
Sample invocation:
one=1 two=2
assert_var_not_null one two
echo test 1: return_code=$?
assert_var_not_null one two three
echo test 2: return_code=$?
assert_var_not_null -f one two three
echo test 3: return_code=$? # this code shouldn't execute
Output:
test 1: return_code=0
Variable 'three' not set
test 2: return_code=1
Variable 'three' not set
More such assertions here: https://github.com/codeforester/base/blob/master/lib/assertions.sh
This can be a way too:
if (set -u; : $HOME) 2> /dev/null
...
...
http://unstableme.blogspot.com/2007/02/checks-whether-envvar-is-set-or-not.html
None of the above solutions worked for my purposes, in part because I checking the environment for an open-ended list of variables that need to be set before starting a lengthy process. I ended up with this:
mapfile -t arr < variables.txt
EXITCODE=0
for i in "${arr[#]}"
do
ISSET=$(env | grep ^${i}= | wc -l)
if [ "${ISSET}" = "0" ];
then
EXITCODE=-1
echo "ENV variable $i is required."
fi
done
exit ${EXITCODE}
Rather than using external shell scripts I tend to load in functions in my login shell. I use something like this as a helper function to check for environment variables rather than any set variable:
is_this_an_env_variable ()
local var="$1"
if env |grep -q "^$var"; then
return 0
else
return 1
fi
}
The $? syntax is pretty neat:
if [ $?BLAH == 1 ]; then
echo "Exists";
else
echo "Does not exist";
fi
I'd like to add an argument to a command in bash only if a variable evaluates to a certain value. For example this works:
test=1
if [ "${test}" == 1 ]; then
ls -la -R
else
ls -R
fi
The problem with this approach is that I have to duplicate ls -R both when test is 1 or if it's something else. I'd prefer if I could write this in one line instead such as this (pseudo code that doesn't work):
ls (if ${test} == 1 then -la) -R
I've tried the following but it doesn't work:
test=1
ls `if [ $test -eq 1 ]; then -la; fi` -R
This gives me the following error:
./test.sh: line 3: -la: command not found
A more idiomatic version of svlasov's answer:
ls $( (( test == 1 )) && printf %s '-la' ) -R
Since echo understands a few options itself, it's safer to use printf %s to make sure that the text to print is not mistaken for an option.
Note that the command substitution must not be quoted here - which is fine in the case at hand, but calls for a more robust approach in general - see below.
However, in general, the more robust approach is to build up arguments in an array and pass it as a whole:
# Build up array of arguments...
args=()
(( test == 1 )) && args+=( '-la' )
args+=( '-R' )
# ... and pass it to `ls`.
ls "${args[#]}"
Update: The OP asks how to conditionally add an additional, variable-based argument to yield ls -R -la "$PWD".
In that case, the array approach is a must: each argument must become its own array element, which is crucial for supporting arguments that may have embedded whitespace:
(( test == 1 )) && args+= ( '-la' "$PWD" ) # Add each argument as its own array element.
As for why your command,
ls `if [ $test -eq 1 ]; then -la; fi` -R
didn't work:
A command between backticks (or its modern, nestable equivalent, $(...)) - a so-called command substitution - is executed just like any other shell command (albeit in a sub-shell) and the whole construct is replaced with the command's stdout output.
Thus, your command tries to execute the string -la, which fails. To send it to stdout, as is needed here, you must use a command such as echo or printf.
Print the argument with echo:
test=1
ls `if [ $test -eq 1 ]; then echo "-la"; fi` -R
I can't say how acceptable this is, but:
test=1
ls ${test:+'-la'} -R
See https://stackoverflow.com/revisions/16753536/1 for a conditional truth table.
Another answer without using eval and using BASH arrays:
myls() { local arr=(ls); [[ $1 -eq 1 ]] && arr+=(-la); arr+=(-R); "${arr[#]}"; }
Use it as:
myls
myls "$test"
This script builds whole command in an array arr and preserves the original order of command options.
How can I test if an associative array is declared in Bash? I can test for a variable like:
[ -z $FOO ] && echo nope
but I doesn't seem to work for associative arrays:
$ unset FOO
$ declare -A FOO
$ [ -z $FOO ] && echo nope
nope
$ FOO=([1]=foo)
$ [ -z $FOO ] && echo nope
nope
$ echo ${FOO[#]}
foo
EDIT:
Thank you for your answers, both seem to work so I let the speed decide:
$ cat test1.sh
#!/bin/bash
for i in {1..100000}; do
size=${#array[#]}
[ "$size" -lt 1 ] && :
done
$ time bash test1.sh #best of five
real 0m1.377s
user 0m1.357s
sys 0m0.020s
and the other:
$ cat test2.sh
#!/bin/bash
for i in {1..100000}; do
declare -p FOO >/dev/null 2>&1 && :
done
$ time bash test2.sh #again, the best of five
real 0m2.214s
user 0m1.587s
sys 0m0.617s
EDIT 2:
Let's speed compare Chepner's solution against the previous ones:
#!/bin/bash
for i in {1..100000}; do
[[ -v FOO[#] ]] && :
done
$ time bash test3.sh #again, the best of five
real 0m0.409s
user 0m0.383s
sys 0m0.023s
Well that was fast.
Thanks again, guys.
In bash 4.2 or later, you can use the -v option:
[[ -v FOO[#] ]] && echo "FOO set"
Note that in any version, using
declare -A FOO
doesn't actually create an associative array immediately; it just sets an attribute on the name FOO which allows you to assign to the name as an associative array. The array itself doesn't exist until the first assignment.
You can use declare -p to check if a variable has been declared:
declare -p FOO >/dev/null 2>&1 && echo "exists" || echo "nope"
And to check specifically associative array:
[[ "$(declare -p FOO 2>/dev/null)" == "declare -A"* ]] &&
echo "array exists" || echo "nope"
This is a Community Wiki version of an excellent answer by #user15483624 on a question which is now closed as duplicate. Should that user choose to add their own answer here, this should be deleted in favor of the one with their name on it.
The prior answers on this question should be used only when compatibility with bash 4.x and prior is required. With bash 5.0 and later, an expansion to check variable type is directly available; its use is far more efficient than parsing the output of declare -p, and it avoids some of the unintended side effects of other proposals as well..
The following can be used to test whether a bash variable is an associative array.
[[ ${x#a} = A ]]
${x#a} can be used to test whether it is a variable and an array as well.
$ declare x; echo "${x#a}"
$ declare -a y; echo "${y#a}"
a
$ declare -A z; echo "${z#a}"
A
One of the easiest ways is to the check the size of the array:
size=${#array[#]}
[ "$size" -lt 1 ] && echo "array is empty or undeclared"
You can easily test this on the command line:
$ declare -A ar=( [key1]=val1 [key2]=val2 ); echo "szar: ${#ar[#]}"
szar: 2
This method allow you to test whether the array is declared and empty or undeclared altogether. Both the empty array and undeclared array will return 0 size.
I want to write a function for when I have something like the following
echo 1 2 3|pick
Pick will then take the arguments and I will do something with them.
How do I do this?
Are you looking for xargs?
pick() {
read -r arg1 arg2 remainder
echo first arg is $arg1
echo The remaining args are $remainder
}
--EDIT (response to question in comment)
One way to loop through the arguments:
pick() {
read args;
set $args;
while test $# -ne 0; do
echo $1
shift
done
}
On each iteration of the loop, $1 refers to an argument.
If I'm not mistaken, the OP wants the same thing I do: you feed it a string, and if the string containes multiple {words,lines}, it presents you a menu, and you pick one, and it returns the one you pick on stdout.
If there's only one item, it just returns it.
This is useful for--to use my particular use-case--a log file viewer script: you give it a substring of a filename, and it greps through find /var/log -name \*$arg\* -print to see what it can find. If it gets a unique hit, it hands it back to your script, which runs less against it. If it gets more than one hit, it shows you a menu, and lets you pick one.
ISTR that KSH has a builtin for this, but that I wasn't all that impressed with it; I don't recall if bash has one.
I am here because I was searching to see if someone had already written it before writing it myself. :-)
UPDATE: Nope; I wrote it myself:
Here's some example code:
/usr/local/bin/msg:
PATH=$PATH:/usr/local/bin
[ $UID = 0 ] || exec sudo su root -c "$0 $*"
FILE=/var/log/messages
[ $# -eq 1 ] &&
FILE=`find /var/log/ -name \*$1\* -print |
egrep -v '2011|.[0-9]$' |
pick`
echo "$FILE"
less +F $FILE
Since I'm piping the name to less +F I want to grep out archived log files; this is for interactive log viewing.
/usr/local/bin/pick:
# Present the user a bash Select menu, and let them pick
# Try to be smart about multi-line responses
# must take input on stdin if it might be multiline
# get multiline input from stdin
while read LINE </dev/stdin
do
CHOICES+=( $LINE )
done
# add on anything specified as arguments
while [ $# -gt 0 ]
do
CHOICES+=( $1 )
shift
done
# if only one thing to pick, just pick it
if [ ${#CHOICES[*]} -eq 1 ]
then
echo $CHOICES
exit
fi
# eval set $CHOICES
select CHOSEN in ${CHOICES[#]}
do
echo $CHOSEN
exit
done </dev/tty
I've got a few Unix shell scripts where I need to check that certain environment variables are set before I start doing stuff, so I do this sort of thing:
if [ -z "$STATE" ]; then
echo "Need to set STATE"
exit 1
fi
if [ -z "$DEST" ]; then
echo "Need to set DEST"
exit 1
fi
which is a lot of typing. Is there a more elegant idiom for checking that a set of environment variables is set?
EDIT: I should mention that these variables have no meaningful default value - the script should error out if any are unset.
Parameter Expansion
The obvious answer is to use one of the special forms of parameter expansion:
: ${STATE?"Need to set STATE"}
: ${DEST:?"Need to set DEST non-empty"}
Or, better (see section on 'Position of double quotes' below):
: "${STATE?Need to set STATE}"
: "${DEST:?Need to set DEST non-empty}"
The first variant (using just ?) requires STATE to be set, but STATE="" (an empty string) is OK — not exactly what you want, but the alternative and older notation.
The second variant (using :?) requires DEST to be set and non-empty.
If you supply no message, the shell provides a default message.
The ${var?} construct is portable back to Version 7 UNIX and the Bourne Shell (1978 or thereabouts). The ${var:?} construct is slightly more recent: I think it was in System III UNIX circa 1981, but it may have been in PWB UNIX before that. It is therefore in the Korn Shell, and in the POSIX shells, including specifically Bash.
It is usually documented in the shell's man page in a section called Parameter Expansion. For example, the bash manual says:
${parameter:?word}
Display Error if Null or Unset. If parameter is null or unset, the expansion of word (or a message to that effect if word is not present) is written to the standard error and the shell, if it is not interactive, exits. Otherwise, the value of parameter is substituted.
The Colon Command
I should probably add that the colon command simply has its arguments evaluated and then succeeds. It is the original shell comment notation (before '#' to end of line). For a long time, Bourne shell scripts had a colon as the first character. The C Shell would read a script and use the first character to determine whether it was for the C Shell (a '#' hash) or the Bourne shell (a ':' colon). Then the kernel got in on the act and added support for '#!/path/to/program' and the Bourne shell got '#' comments, and the colon convention went by the wayside. But if you come across a script that starts with a colon, now you will know why.
Position of double quotes
blong asked in a comment:
Any thoughts on this discussion? https://github.com/koalaman/shellcheck/issues/380#issuecomment-145872749
The gist of the discussion is:
… However, when I shellcheck it (with version 0.4.1), I get this message:
In script.sh line 13:
: ${FOO:?"The environment variable 'FOO' must be set and non-empty"}
^-- SC2086: Double quote to prevent globbing and word splitting.
Any advice on what I should do in this case?
The short answer is "do as shellcheck suggests":
: "${STATE?Need to set STATE}"
: "${DEST:?Need to set DEST non-empty}"
To illustrate why, study the following. Note that the : command doesn't echo its arguments (but the shell does evaluate the arguments). We want to see the arguments, so the code below uses printf "%s\n" in place of :.
$ mkdir junk
$ cd junk
$ > abc
$ > def
$ > ghi
$
$ x="*"
$ printf "%s\n" ${x:?You must set x} # Careless; not recommended
abc
def
ghi
$ unset x
$ printf "%s\n" ${x:?You must set x} # Careless; not recommended
bash: x: You must set x
$ printf "%s\n" "${x:?You must set x}" # Careful: should be used
bash: x: You must set x
$ x="*"
$ printf "%s\n" "${x:?You must set x}" # Careful: should be used
*
$ printf "%s\n" ${x:?"You must set x"} # Not quite careful enough
abc
def
ghi
$ x=
$ printf "%s\n" ${x:?"You must set x"} # Not quite careful enough
bash: x: You must set x
$ unset x
$ printf "%s\n" ${x:?"You must set x"} # Not quite careful enough
bash: x: You must set x
$
Note how the value in $x is expanded to first * and then a list of file names when the overall expression is not in double quotes. This is what shellcheck is recommending should be fixed. I have not verified that it doesn't object to the form where the expression is enclosed in double quotes, but it is a reasonable assumption that it would be OK.
Try this:
[ -z "$STATE" ] && echo "Need to set STATE" && exit 1;
Your question is dependent on the shell that you are using.
Bourne shell leaves very little in the way of what you're after.
BUT...
It does work, just about everywhere.
Just try and stay away from csh. It was good for the bells and whistles it added, compared the Bourne shell, but it is really creaking now. If you don't believe me, just try and separate out STDERR in csh! (-:
There are two possibilities here. The example above, namely using:
${MyVariable:=SomeDefault}
for the first time you need to refer to $MyVariable. This takes the env. var MyVariable and, if it is currently not set, assigns the value of SomeDefault to the variable for later use.
You also have the possibility of:
${MyVariable:-SomeDefault}
which just substitutes SomeDefault for the variable where you are using this construct. It doesn't assign the value SomeDefault to the variable, and the value of MyVariable will still be null after this statement is encountered.
Surely the simplest approach is to add the -u switch to the shebang (the line at the top of your script), assuming you’re using bash:
#!/bin/sh -u
This will cause the script to exit if any unbound variables lurk within.
${MyVariable:=SomeDefault}
If MyVariable is set and not null, it will reset the variable value (= nothing happens).
Else, MyVariable is set to SomeDefault.
The above will attempt to execute ${MyVariable}, so if you just want to set the variable do:
MyVariable=${MyVariable:=SomeDefault}
In my opinion the simplest and most compatible check for #!/bin/sh is:
if [ "$MYVAR" = "" ]
then
echo "Does not exist"
else
echo "Exists"
fi
Again, this is for /bin/sh and is compatible also on old Solaris systems.
bash 4.2 introduced the -v operator which tests if a name is set to any value, even the empty string.
$ unset a
$ b=
$ c=
$ [[ -v a ]] && echo "a is set"
$ [[ -v b ]] && echo "b is set"
b is set
$ [[ -v c ]] && echo "c is set"
c is set
I always used:
if [ "x$STATE" == "x" ]; then echo "Need to set State"; exit 1; fi
Not that much more concise, I'm afraid.
Under CSH you have $?STATE.
For future people like me, I wanted to go a step forward and parameterize the var name, so I can loop over a variable sized list of variable names:
#!/bin/bash
declare -a vars=(NAME GITLAB_URL GITLAB_TOKEN)
for var_name in "${vars[#]}"
do
if [ -z "$(eval "echo \$$var_name")" ]; then
echo "Missing environment variable $var_name"
exit 1
fi
done
We can write a nice assertion to check a bunch of variables all at once:
#
# assert if variables are set (to a non-empty string)
# if any variable is not set, exit 1 (when -f option is set) or return 1 otherwise
#
# Usage: assert_var_not_null [-f] variable ...
#
function assert_var_not_null() {
local fatal var num_null=0
[[ "$1" = "-f" ]] && { shift; fatal=1; }
for var in "$#"; do
[[ -z "${!var}" ]] &&
printf '%s\n' "Variable '$var' not set" >&2 &&
((num_null++))
done
if ((num_null > 0)); then
[[ "$fatal" ]] && exit 1
return 1
fi
return 0
}
Sample invocation:
one=1 two=2
assert_var_not_null one two
echo test 1: return_code=$?
assert_var_not_null one two three
echo test 2: return_code=$?
assert_var_not_null -f one two three
echo test 3: return_code=$? # this code shouldn't execute
Output:
test 1: return_code=0
Variable 'three' not set
test 2: return_code=1
Variable 'three' not set
More such assertions here: https://github.com/codeforester/base/blob/master/lib/assertions.sh
This can be a way too:
if (set -u; : $HOME) 2> /dev/null
...
...
http://unstableme.blogspot.com/2007/02/checks-whether-envvar-is-set-or-not.html
None of the above solutions worked for my purposes, in part because I checking the environment for an open-ended list of variables that need to be set before starting a lengthy process. I ended up with this:
mapfile -t arr < variables.txt
EXITCODE=0
for i in "${arr[#]}"
do
ISSET=$(env | grep ^${i}= | wc -l)
if [ "${ISSET}" = "0" ];
then
EXITCODE=-1
echo "ENV variable $i is required."
fi
done
exit ${EXITCODE}
Rather than using external shell scripts I tend to load in functions in my login shell. I use something like this as a helper function to check for environment variables rather than any set variable:
is_this_an_env_variable ()
local var="$1"
if env |grep -q "^$var"; then
return 0
else
return 1
fi
}
The $? syntax is pretty neat:
if [ $?BLAH == 1 ]; then
echo "Exists";
else
echo "Does not exist";
fi