What does echo $? mean in shell programming? 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 non-zero return status means failure. Learn more about exit statuses on wikipedia. There are other special ...
What does $# mean in shell? I have code such as if [ $# -eq 0 ] then I want to understand what $# means, but Google search is very bad for searching these kinds of things.
$(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 ...
I'm trying to learn shell scripting, and I need to understand someone else's code. What is the $? variable hold? I can't Google search the answer because they block punctuation characters.
$! is the PID of the most recent background command. $0 is the name of the shell or shell script. Most of the above can be found under Special Parameters in the Bash Reference Manual. Here are all the environment variables set by the shell. For a comprehensive index, please see the Reference Manual Variable Index.
In shell scripts, what is the difference between $@ and $*? Which one is the preferred way to get the script arguments? Are there differences between the different shell interpreters about this?
The shell will try to create directory test and then, only if it was successful will try create file inside it. So you may interrupt a sequence of steps if one of them failed.
