In Bash, there appear to be several variables which hold special, consistently-meaning values. For instance,
./myprogram &; echo $!
will return the PID of the process which backgrounded myprogram. I know of others, such as $? which I think is the current TTY. Are there others?
This question is related to
bash
environment-variables
dollar-sign
To help understand what do $#, $0 and $1, ..., $n do, I use this script:
#!/bin/bash
for ((i=0; i<=$#; i++)); do
echo "parameter $i --> ${!i}"
done
Running it returns a representative output:
$ ./myparams.sh "hello" "how are you" "i am fine"
parameter 0 --> myparams.sh
parameter 1 --> hello
parameter 2 --> how are you
parameter 3 --> i am fine
Take care with some of the examples; $0 may include some leading path as well as the name of the program. Eg save this two line script as ./mytry.sh and the execute it.
#!/bin/bash
echo "parameter 0 --> $0" ; exit 0
Output:
parameter 0 --> ./mytry.sh
This is on a current (year 2016) version of Bash, via Slackware 14.2
$_ last argument of last command$# number of arguments passed to current script$* / $@ list of arguments passed to script as string / delimited listoff the top of my head. Google for bash special variables.
Source: Stackoverflow.com