- 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 - 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
- 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)?
- 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?
- 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
- Which characters need to be escaped when using Bash?
Is there any comprehensive list of characters that need to be escaped in Bash? Can it be checked just with sed? In particular, I was checking whether % needs to be escaped or not I tried echo "h
- 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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