Bash Shell Scripting/External Programs

Bash, as a shell, is actually a 'glue' language. It helps programs to cooperate with each other, and benefits from it. Always Search The Internet for what you want -- there are lots of command line utilities available.

Using whiptail

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Whiptail is a program that allows shell scripts to display dialog boxes to the user for informational purposes, or to get input from the user in a friendly way. Whiptail is included by default on Debian and various other GNU/Linux distributions.

From the GNU/Linux Dictionary: whiptail is a "dialog" replacement using newt instead of ncurses.
From its README: whiptail is designed to be drop-in compatible with dialog(1), but has fewer features: some dialog boxes are not implemented, such as tailbox, timebox, calendarbox, etc.

See Bash Shell Scripting/Whiptail.

Using AWK

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See AWK and man awk (man gawk).

Using sed

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See sed and man sed.

See grep and man grep.

Using man, info and help

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These three programs are where you can find help or reference from. man displays roff manual pages, info displays texinfo documentations, while help displays builtin helps.

Appending --long-help, --help or --usage to a command-line program may also gives you the usage information. Possible synonyms include -H and -h.

Just try these out:

man --help
man man

info --help
man info
info info

help help

Pressing h in man and info's interfaces can also give you some direction.