What is the $? (dollar question mark) variable in shell scripting? The shell treats several parameters specially These parameters may only be referenced; assignment to them is not allowed [ ]? Expands to the exit status of the most recently executed foreground pipeline ANSI C and POSIX then recommend that: 0 means the program was successful other values: the program failed somehow
linux - What does $@ mean in a shell script? - Stack Overflow The shell splits tokens based on the contents of the IFS environment variable Its default value is \t\n; i e , whitespace, tab, and newline Expanding "$@" gives you a pristine copy of the arguments passed Expanding $@ may not
Difference between $ {} and $ () in a shell script - Super User The above (along with many more forms of ${parameter…something_else} constructs) are discussed at greater length in the shell’s man page, bash(1) A Note on Quotes Note that you should always quote shell variables unless you have a good reason not to, and you’re sure you know what you’re doing By contrast, while braces can be
regex - Meaning of =~ operator in shell script - Stack Overflow The return value is 0 if the string matches the pattern, and 1 otherwise If the regular expression is syntactically incorrect, the conditional expression's return value is 2 If the shell option nocasematch is enabled, the match is performed without regard to the case of alphabetic characters
What does $# mean in shell? - Unix Linux Stack Exchange You can always check the man page of your shell man bash says: Special Parameters # Expands to the number of positional parameters in decimal Therefore a shell script can check how many parameters are given with code like this: if [ "$#" -eq 0 ]; then echo "you did not pass any parameter" fi
What is the meaning of $? in a shell script? - linux This latter usage is faster, does not contaminate the shell's variable namespace with what amounts to temp variables, can often be a lot more readable for humans and encourages the use of "positive logic", the practice of writing conditionals without negations, which has cognitive simplicity in most situations
shell - Difference between sh and Bash - Stack Overflow Shell - "Shell" is a program, which facilitates the interaction between the user and the operating system (kernel) There are many shell implementations available, like sh, Bash, C shell, Z shell, etc Using any of the shell programs, we will be able to execute commands that are supported by that shell program Bash - It derived from Bourne
