- 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
- 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
- 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
- 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
- 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
- What is the difference between single and double square brackets in Bash?
Ubuntu 16 04 actually has an executable for it at usr bin [ provided by coreutils, but the bash built-in version takes precedence Nothing is altered in the way that Bash parses the command In particular, < is redirection, and || concatenate multiple commands, ( ) generates subshells unless escaped by \, and word expansion happens as usual
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