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In computer programming, string interpolation (or variable interpolation, variable substitution, or variable expansion) is the process of evaluating a string literal containing one or more placeholders, yielding a result in which the placeholders are replaced with their corresponding values.
$0 is the name of the script itself (script.sh) $1 is the first argument (filename1) $2 is the second argument (dir1)
$_ (dollar underscore) is another special bash parameter and used to reference the absolute file name of the shell or bash script which is being executed as specified in the argument list. This bash parameter is also used to hold the name of mail file while checking emails.
${} Parameter Substitution/Expansion A parameter, in Bash, is an entity that is used to store values. A parameter can be referenced by a number, a name, or by a special symbol. When a parameter is referenced by a number, it is called a positional parameter.
Use
"$filepath"_newstap.sh
or
${filepath}_newstap.sh
or
$filepath\_newstap.sh
_ is a valid character in identifiers. Dot is not, so the shell tried to interpolate $filepath_newstap.
You can use set -u to make the shell exit with an error when you reference an undefined variable.
Use curly braces around the variable name:
`tail -1 ${filepath}_newstap.sh`
In Bash:
tail -1 ${filepath}_newstap.sh
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