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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
Difference between ${} and $() in a shell script - Super User $(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 , $ ls -ld $(date +%B) txt -rwxr-xr-x 1 Noob Noob 867 Jul 2 11:09 July txt ${parameter} is “parameter substitution” A lot of information can be found in the shell’s man page, bash (1), under the “ Parameter
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
shell - What does -- (double dash double hyphen) mean? - Unix . . . In man bash we can read in Shell Builtin Commands section (online doc): Unless otherwise noted, each builtin command documented in this section as accepting options preceded by - accepts -- to signify the end of the options The :, true, false, and test builtins do not accept options and do not treat -- specially The exit, logout, break, continue, let, and shift builtins accept and process
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
Meaning of $? (dollar question mark) in shell scripts This is the exit status of the last executed command For example the command true always returns a status of 0 and false always returns a status of 1: true echo $? # echoes 0 false echo $? # echoes 1 From the manual: (acessible by calling man bash in your shell) ? Expands to the exit status of the most recently executed foreground pipeline By convention an exit status of 0 means success, and