Bash

1. Information

Type the following command in a terminal to see which shell you are using.

echo $0                 # -bash         # When inside bash shell.
echo $0                 # sh            # When inside dash shell.

2. Shell Parameter Expansion

bash shell: See https://www.gnu.org/software/bash/manual/html_node/Shell-Parameter-Expansion.html

dash shell: See https://man7.org/linux/man-pages/man1/dash.1.html and look for Parameter Expansion.

${parameter#word}           expands to <parameter> with prefix <word> deleted.
${parameter/pattern/string} expands to <parameter> with <pattern> replaced by <string>.

# Examples.
var="abcdef"; echo -n ${var}; echo -n " --> "; echo ${var#abc}          # abcdef --> def
var="abcdef"; echo -n ${var}; echo -n " --> "; echo ${var/abc/xxx}      # abcdef --> xxxdef