A lot of information can be found in the shell’s man page, bash(1), under the “Parameter Expansion” heading: ${ parameter } The value of parameter is substituted.

the number of parameters with which the script has been called. the number of parameters which have been set within the script by set -- foo bar (when used within a function) the number of parameters with which a function has been called (set would work there, too). This is explained in the bash man page in the block "Special Parameters".

Feb 20, 2011 · $0-The filename of the current script. $#-The number of arguments supplied to a script. $$-The process number of the current shell. For shell scripts, this is the process ID under which they are executing.

See What is the difference between > and >> (especially as it relates to use with the cat program)?, What does “3>&1 1>&2 2>&3” do in a script? and of course, your shell's manual. (There are some further explanations in Is this a typo in Bash manual's redirection section? too.) –

You can find a very nice reference for bash's [aka test builtin's operators here, or by running help test in a bash shell or info bash test or info bash '[' from any shell¹. If you are using a different shell, just search for the description of its [ or test builtin in its documentation of if it doesn't have such a builtin², in the man page ...

Which shell exactly depends on the system. Example for a system that uses bash as its standard shell: $ ls -l /bin/sh lrwxrwxrwx 1 root root 4 Mar 13 16:12 /bin/sh -> bash $ sh --version GNU bash, version 4.2.45(1)-release (x86_64-pc-linux-gnu) sys-snap.sh will be a shell script of some kind, so sh sys-snap.sh will execute the shell script.

The question doesn't mention bash, and in fact deliberately only mentions shell script, both in the tags, and in the question. This answer would fail in a POSIX environment. This answer would fail in a POSIX environment.

awk '{$1=$1;print}' or shorter: awk '{$1=$1};1' Would trim leading and trailing space or tab characters 1 and also squeeze sequences of tabs and spaces into a single space.

Your script is missing a #! line at the start, which is the magic interpreted by the kernel to say which command interpreter is to be used for the script. Make it look like this: #!/bin/sh notify-send "hi welcome" and make sure the script is executable: ls -l home/hacks/notify.sh chmod +x home/hacks/notify.sh ls -l home/hacks/notify.sh

Nov 27, 2015 · Shell script: ssh to remote machine, then exit: 'exit' does not work. 2. How to set a time length of ssh ...