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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
- What do the -n and -a options do in a bash if statement?
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 is a command that takes a command as its argument, executes it and tests its return code
- How do I iterate over a range of numbers defined by variables in Bash?
Related discusions: bash for loop: a range of numbers and unix stackexchange com - In bash, is it possible to use an integer variable in the loop control of a for loop?
- An and operator for an if statement in Bash - Stack Overflow
Modern shells such as Bash and Zsh have inherited this construct from Ksh, but it is not part of the POSIX specification If you're in an environment where you have to be strictly POSIX compliant, stay away from it; otherwise, it's basically down to personal preference
- How to compare strings in Bash - Stack Overflow
How do I compare a variable to a string (and do something if they match)?
- bash - Difference between if -e and if -f - Stack Overflow
59 $ man bash -e file True if file exists -f file True if file exists and is a regular file A regular file is something that isn't a directory, symlink, socket, device, etc
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