I have a very small piece of code. And i am not sure where i am making it wrong. This is a simple IF condition, which should work.
#!/bin/bash
flag1=$1
flag2=$2
if [ "$flag1"="C" ] && [ "$flag2"="C" ]
then
echo "Proceed"
else
echo "Fail"
fi
I am running it using :- sh testif.sh C A and sh testif.sh C C
And i am getting same result in both. Proceed
I am new to Unix Scripting. Please tell me what blunder i am doing.
Sorry, for asking such a basic question.
You want space in between your bash tokens:
if [ "$flag1" = "C" ] && [ "$flag2" = "C" ]
= is just fine, but you're right about the spaces.
= operator is equivalent to == (just read from man bash). Edited answer accordingly.bash does is to break your input line into tokens roughly seperated by white space, then it looks at those token to parse the line. So you end up giveng bash the single token "$flag1"="C" which doesn't compute as a logical expression.
= and == are equivalent in bash, but == is a syntax error is some shells.
= and == are only equivalent in the [[ builtin, for [ the = operator is strictly string equality. Compare: [[ "bar" = *a* ]] && echo y outputs "y" but [ "bar" = *a* ] && echo y outputs bash: [: too many arguments (depending on the contents of your current directory)Paul Evans's answer has the proper solution: you need (at least) a space character around operators such as = (and its equivalent in bash, ==).
As for why you needed that space:
Bash allows string concatenation simply by placing tokens next to each other without whitespace in between. Whether the tokens are quoted or not, and what quotes are used is irrelevant; e.g.:
'ab'cd"ef" # -> Bash sees: abcdef
In the case at hand:
"$flag1"="C" # Bash eventually sees: <value-of-$flag1>=C
In other words: "$flag1"="C" evaluates to a single, nonempty string literal, and applying [ ... ] to such a string always evaluates to true.
Generally, see http://pubs.opengroup.org/onlinepubs/9699919799/utilities/test.html#tag_20_128 in the POSIX shell spec. for information on how [ and its alias test treat differing numbers of arguments (thanks, @glennjackman).
For Bash to recognize the intended syntactic elements of "$flag1"="C" as such, you must therefore separate the elements with at least one space each.: "$flag1" = "C"
If you want your solution to be more bash-like, however, consider use of [[ ... ]] rather than POSIX syntax [ ... ]:
if [[ $flag1 == "C" && $flag2 == "C" ]] # ...
Benefits:
&& inside a single [[ ... ]] construct.= / == to distinguish string literals from patterns).Compatibility note: While [[ ... ]] works in bash and also zsh and ksh (though the behavior differs subtly), it is NOT POSIX-compliant. In situations where that is a concern, stick with [ ... ].
[ (and test) does when given different numbers of arguments. (posix manual for test)
=signs.sh testif.shwill override the shebang, forcing this to be interpreted asshinstead ofbash?#!/bin/bashdefines the default interpreter for the script in question -- the interpreter used if no interpreter is called explicitly (e.g. when you'd be calling./testif.shdirectly). When you're callingsh testif.sh, you are specifyingshto interpret the script. Now, most systems make/usr/bin/sha link to/bin/bash-- but if invoked this way, bash will run in compatibility mode, mimicking originalshbehaviour. Stuff like this can result in surprising errors -- for example, redirecting script output viaexec > >(tee logfile.txt)will not work inshmode.