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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
The [[ ]] is treated specially by bash; consider that an augmented version of [ ] construct: [ ] is actually a shell built-in command, which, can actually be implemented as an external command Look at your usr bin, there is most likely a program called "[" there! Strictly speaking, [ ] is not part of bash syntax
- bash - What is the purpose of in a shell command? - Stack Overflow
As far as I know, using amp; after the command is for running it in the background Example of amp; usage: tar -czf file tar gz dirname amp; But how about amp; amp;? (example)
- bash - Shell equality operators (=, ==, -eq) - Stack Overflow
If not quoted, it is a pattern match! (From the Bash man page: "Any part of the pattern may be quoted to force it to be matched as a string ") Here in Bash, the two statements yielding "yes" are pattern matching, other three are string equality:
- Meaning of $? (dollar question mark) in shell scripts
In Bash, when you hit enter, a fork + exec + wait happens like above, and bash then sets $? to the exit status of the forked process Note: for built-in commands like echo, a process need not be spawned, and Bash just sets $? to 0 to simulate an external process Standards and documentation
- linux - What does $@ mean in a shell script? - Stack Overflow
(View Special parameters - Bash Manual) For instance, if you call someScript sh foo bar then $@ will be equal to foo bar If you do: someScript sh foo bar and then inside someScript sh reference: umbrella_corp_options "$@"
- How do AND and OR operators work in Bash? - Stack Overflow
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
- Whats the difference between lt; lt;, lt; lt; lt; and lt; lt; in bash?
In bash these are implemented via temp files, usually in the form tmp sh-thd <random string>, while in dash they are implemented as anonymous pipes This can be observed via tracing system calls with strace command Replace bash with sh to see how bin sh performs this redirection $ strace -e open,dup2,pipe,write -f bash -c 'cat <<EOF > test
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