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- bash - What are the special dollar sign shell variables . . . - Stack . . .
In Bash, there appear to be several variables which hold special, consistently-meaning values For instance, myprogram amp;; echo $! will return the PID of the process which backgrounded myprog
- shell - Bash regex =~ operator - Stack Overflow
What is the operator =~ called? I'm not sure it has a name The bash documentation just calls it the =~ operator Is it only used to compare the right side against the left side? The right side is considered an extended regular expression If the left side matches, the operator returns 0, and 1 otherwise Why are double square brackets required when running a test? Because =~ is an operator of
- bash - What is the purpose of in a shell command? - Stack Overflow
$ command one command two the intent is to execute the command that follows the only if the first command is successful This is idiomatic of Posix shells, and not only found in Bash It intends to prevent the running of the second process if the first fails You may notice I've used the word "intent" - that's for good reason
- bash - Shell equality operators (=, ==, -eq) - Stack Overflow
It depends on the Test Construct around the operator Your options are double parentheses, double brackets, single brackets, or test If you use ((…)), you are testing arithmetic equality with == as in C: $ (( 1==1 )); echo $? 0 $ (( 1==2 )); echo $? 1 (Note: 0 means true in the Unix sense and a failed test results in a non-zero number ) Using -eq inside of double parentheses is a syntax
- Whats the difference between lt; lt;, lt; lt; lt; and lt; lt; in bash?
What's the difference between <<, <<< and < < in bash?Here document << is known as here-document structure You let the program know what will be the ending text, and whenever that delimiter is seen, the program will read all the stuff you've given to the program as input and perform a task upon it Here's what I mean: $ wc << EOF > one two three > four five > EOF 2 5 24 In this example we
- arguments - What is $@ in Bash? - Stack Overflow
I reckon that the handle $@ in a shell script is an array of all arguments given to the script Is this true? I ask because I normally use search engines to gather information, but I can't google f
- An and operator for an if statement in Bash - Stack Overflow
An "and" operator for an "if" statement in Bash Asked 12 years, 7 months ago Modified 12 months ago Viewed 972k times
- What do the -n and -a options do in a bash if statement?
Nitpicking The switches -a and -n are not strictly part of a bash if statement in that the if command does not process these switches What are primaries? I call them "switches", but the bash documentation that you linked to refers to the same thing as "primaries" (probably because this is a common term used when discussing parts of a boolean expression) Background and docs In sh scripts if
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