sometimes I just forgot the syntax of using if, while or for. Sometimes I am not sure the syntax i used is it correct. Let say I wanna refers back how to use
square bracket ( [ ] ), by specified
It leads me to a lengthy BASH_BINUTILS manual, which cause me more headache. I discover a good command which can help me a bit better, its call
The result I get is
[: [ arg... ] This is a synonym for the "test" builtin, but the last argument must be a literal `]', to match the opening `['. [[ ... ]]: [[ expression ]] Returns a status of 0 or 1 depending on the evaluation of the conditional expression EXPRESSION. Expressions are composed of the same primaries used by the `test' builtin, and may be combined using the following operators ( EXPRESSION ) Returns the value of EXPRESSION ! EXPRESSION True if EXPRESSION is false; else false EXPR1 && EXPR2 True if both EXPR1 and EXPR2 are true; else false EXPR1 || EXPR2 True if either EXPR1 or EXPR2 is true; else false When the `==' and `!=' operators are used, the string to the right of the operator is used as a pattern and pattern matching is performed. The && and || operators do not evaluate EXPR2 if EXPR1 is sufficient to determine the expression's value.
Isn’t it better? If you still find it difficult, then remember to refers here : ) LBE have a category for Bash.
To get more shorter reference help, specified with -s, for example:
help -s if
This will show the result as bellow:
if: if COMMANDS; then COMMANDS; [ elif COMMANDS; then COMMANDS; ]... [ else COMMANDS; ] fi