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
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
How to conditionally do something if a command succeeded or failed It's probably the most common command to use in an if, which can lead to the assumption that it's part of the shell's syntax But if you want to test whether a command succeeded or not, use the command itself directly with if, as shown above
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
windows - How to run a PowerShell script - Stack Overflow Double-clicking it in Explorer produces the same result "File type association" (without further specification) means the default ("open") shell command "Calling the file directly" as in the 1st example only works from powershell prompt -- and only if the path doesn't have spaces –
string - Extract substring in Bash - Stack Overflow expr is an artifact of the 1970s; as an external command that needs to be forked off as a subprocess, it's deeply inefficient compared to modern shell builtins – Charles Duffy Commented Nov 18, 2021 at 20:30
shell script - What does -s and - Unix Linux Stack Exchange The -s test returns true if [ ] if file exists and has a size greater than zero This is documented in the bash manual, and also in the manual for the test utility (the test may also be written if test -s file; then)
What is the purpose of in a shell command? - Stack Overflow In shell, when you see $ 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