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While learning a bit about bash, I come to see four types of ways of working with if statements:
What is the difference between Parenthesis and Square Brackets in bash.
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3. Brackets are used to enclose parenthetical materials within the parentheses while parentheses are used to enclose words, numbers, phrases, sentences, symbols, and other items in a sentence.
( Single Parentheses ) This means that they run through all of the commands inside, and then return a single exit code. Any variables declared or environment changes will get cleaned up and disappeared.
Double Brackets i.e. [[]] is an enhanced (or extension) version of standard POSIX version, this is supported by bash and other shells(zsh,ksh). In bash, for numeric comparison we use eq , ne , lt and gt , with double brackets for comparison we can use == , !=
so you can use this if you want to print the name of shell script. $- $- (dollar hyphen) bash parameter is used to get current option flags specified during the invocation, by the set built-in command or set by the bash shell itself. Though this bash parameter is rarely used. $?
The tests you had listed :
test test but more powerful)are not exhaustive, you can use boolean logic
if command; then ... too, because the commands have exit status. In bash, 0 is true and > 0 is false.
You can see the exit status like this :
command echo $? See :
http://wiki.bash-hackers.org/syntax/basicgrammar
http://wiki.bash-hackers.org/syntax/arith_expr
http://mywiki.wooledge.org/BashGuide/TestsAndConditionals
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