使用重定向的stdin调用man来显示BASH脚本中的帮助

Question

Is there any reason why using man with redirected stdin to show help from within a BASH script is a bad idea or not compatible with all (within reason) versions of BASH?

The technique works fine with the 2 versions of BASH that I have easy access to: GNU BASH v. 4.3.11 and 4.3.30 (both on Linux). It seems to me an elegant way to display help for a script, from within the script, when the people who download it are not particularly likely to bother installing the man page, and the man page has already been written.

Below is a bare-bones example of what I mean. The display_usage_message function would get called when the help option is used on the command line and the script would call exit when the function returns.

#!/bin/bash

display_usage_message()
{
man /dev/stdin <<EOF

.TH SCRIPT 1 "01 Oct 2015" "1.0" "SCRIPT VERSION 1.0"

.SH NAME
Script \- whatever it does.

.SH SYNOPSIS
script options etc.

.SH DESCRIPTION
This is a description which is not very long. :)
EOF
}

display_usage_message
exit

Thanks.

EDIT: In light of chepner's comment, would this slight variation be reliable?

#!/bin/bash

display_usage_message()
{

temp_man_filename=$(mktemp -q -t "tmp.man.page.XXXXXX")

cat <<EOF >>$temp_man_filename

.TH SCRIPT 1 "01 Oct 2015" "1.0" "SCRIPT VERSION 1.0"

.SH NAME
Script \- whatever it does.

.SH SYNOPSIS
script options etc.

.SH DESCRIPTION
This is a description which is not very long. :)
EOF

man $temp_man_filename

rm $temp_man_filename
}

display_usage_message
exit

Answer 1

The expectation is for the help message to be a short -- ideally, less than a screenful -- reminder of the available functionality, while the manual, conversely, should explain concepts and document error messages, exit codes, operational constraints, etc.

More fundamentally, keeping some or all of the documentation embedded in, or coupled with, the source code is good practice, actively promoted eg in Knuth's Literate Programming and practiced (perhaps less strictly and formally) by eg Perl POD and Javadoc authors.

Incidentally, man markup feels somewhat obscure in this day and age. Perhaps you would want to explore POD or Markdown as friendlier, more modern alternatives (though not quite as versatile for advanced use). POD is easy enough to embed in shell scripts, and formatting tools will be installed anywhere you have Perl.