- What is the $? (dollar question mark) variable in shell scripting?
344 $? is used to find the return value of the last executed command Try the following in the shell: ls somefile echo $? If somefile exists (regardless whether it is a file or directory), you will get the return value thrown by the ls command, which should be 0 (default "success" return value)
- regex - Meaning of =~ operator in shell script - Stack Overflow
An additional binary operator, =~, is available, with the same precedence as == and != When it is used, the string to the right of the operator is considered an extended regular expression and matched accordingly (as in regex (3)) The return value is 0 if the string matches the pattern, and 1 otherwise
- bash - Shell equality operators (=, ==, -eq) - Stack Overflow
Bash variables are untyped so [[ "yes" -eq "no" ]] is equivalent to [[ "yes" -eq 0 ]] or [[ "yes" -eq "any_noninteger_string" ]] -- All True The -eq forces integer comparison The "yes" is interpreted as a integer 0; the comparison is True if the other integer is either 0 or the string result is 0
- Difference between $ {} and $ () in a shell script - Super User
76 $(command) is “command substitution” As you seem to understand, it runs the command, captures its output, and inserts that into the command line that contains the $(…); e g , ${parameter} is “parameter substitution” A lot of information can be found in the shell’s man page, bash (1), under the “ Parameter Expansion ” heading:
- 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
- Bash Script : what does #! bin bash mean? - Stack Overflow
8 @ShivanRaptor #! bin bash Means run this script in bash #! bin sh means run this script in sh which is the default unix shell, which might be bash or any other variant like ksh, dash, zsh, etc – Karthik T Dec 14, 2012 at 3:10 When bash is run as sh, it behaves differently (more POSIX-like) than when it is run as bash
- 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
- 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
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