I am running some script which passing the string argument and I want to do if else statement shown as below:
if [ $1 != '' ] && [ $2 != '' ]
then do something.....but it shown Error too many argument. Why?
5 Answers
Try using the -z test:
if [ -z "$1" ] && [ -z "$2" ]From man bash:
-z string True if the length of string is zero.Since this is tagged bash, I recommend that one use the extended test construct ([[...]]), and forget the quotes:
if [[ -z $1 && -z $2 ]]; then
...Unless you are going for sh/POSIX compatibility, there is no reason not to use [[ ]].
The following also works,
if [ "$1" == "" && "$2" == ""]; then echo NULL
fiFor the old version of the answer, see the second portion of this answer. If you want to know about details, read on
The cause of issue
In the question itself, it is reported that OP sees too many arguments error, which when tested in bash doesn't seem to be the case:
$ [ $1 != '' ] && [ $2 != '' ]
bash: [: !=: unary operator expectedWith /bin/sh which is actually symlinked to /bin/dash on Ubuntu, error reported as follows:
$ sh
$ [ $1 != '' ] && [ $2 != '' ]
sh: 1: [: !=: unexpected operatorAnd the standalone /bin/test also :
$ /usr/bin/test $1 != ''
/usr/bin/test: missing argument after ‘’Sidenote: If you're wondering what is /usr/bin/test and why I'm using bash and sh, then you should know that [ is alias for test command, which also exists as standalone executable or more commonly - as shell built-in which is what each shell will use first. As for if statements, they operate on exit statues of commands, hence why [ and test are commands, with everything else being arguments to that commands - improper order of those command-line args leads to errors.
Back to the topic: it's unclear how OP got the unrelated error. However, in all 3 cases the issue is the same - unset variable will be treated as empty, thus what the shell sees with these unquoted variables is
[ != '' ]which breaks syntax which test understands. Remember what I said about improper order of command-line arguments ? Hence why quoting is important. Let's enable diagnostic output and see what shell executes:
$ set -x
# throws error
$ [ $1 != '' ] && [ $2 != '' ]
+ '[' '!=' '' ']'
bash: [: !=: unary operator expected
# no error
$ [ "$1" != '' ] && [ "$2" != '' ] || echo null vars
+ '[' '' '!=' '' ']'
+ echo null vars
null varsBetter way to test unset variables
A very frequent approach that you see around is this:
if [ "x$var1" == "x" ] && [ "x$var2" == "x" ]; then echo "both variables are null" fiTo quote Gilles:
In [ "x$1" = "x" ], the x prefix ensures that x"$1" cannot possibly look like an operator, and so the only way the shell can parse this test is by treating = as a binary operator.
Presumably, this should be fairly portable since I've seen these in /bin/sh scripts. It also can be combined as in
if [ "x${var1}${var2}" == "x" ]; then ...
fiOf course we could use -z flag, however according to research in some shells, particularly ksh88 (according to Stephane Chazelas), this flag is faulty.
See also
1I think the title of the post is not accurate, as the intention in the message was to check if $1 and $2 are not null. The given example was just missing double quotes in $1 and $2 to work. Variables must be double quoted to be expanded when comparing strings. But, to check if $1 and $2 exist is the same as check if $2 exist, as it can't exist if $1 doesn't. The 'if' command is also not needed in this case, as 'test' returns true/false and uses '&&' as 'then' if return is 0/true:
[ "$2" != '' ] && commands...Simpler, with -n (nonzero):
[ -n "$2" ] && commands...To "check if $1 and $2 are null" would be the same as check if there is no parameter:
[ $# -eq 0 ] && commands...
