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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
- 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
- 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
- linux - What does $@ mean in a shell script? - Stack Overflow
What does a dollar sign followed by an at-sign (@) mean in a shell script? For example: umbrella_corp_options $@
- Meaning of $? (dollar question mark) in shell scripts
This is the exit status of the last executed command For example the command true always returns a status of 0 and false always returns a status of 1: true echo $? # echoes 0 false echo $? # echoes 1 From the manual: (acessible by calling man bash in your shell) ? Expands to the exit status of the most recently executed foreground pipeline By convention an exit status of 0 means success, and
- How do AND and OR operators work in Bash? - Stack Overflow
8 In bash, and || have equal precendence and associate to the left See Section 3 2 3 in the manual for details So, your example is parsed as $ (echo this || echo that) echo other And thus only the left-hand side of the or runs, since that succeeds the right-hand side doesn't need to run
- 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 11 months ago Viewed 971k times
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