Question

I wrote a script that takes a bunch of options (-d, -v, -l, as well as --version, --leader, etc…) and then the rest of the text ($*) can be anything. The script processes the text and spits it out reformatted. It’s quite long, so here’s a condensed version:

## –––––––––––––––––––––––––[ myScript.sh ]–––––––––––––––––––––––––– ##

# (1) Set up default values

declare -- v='1.0' FS=$':\n\r\v\f\t'  Application='Finder' Files s='s'
declare -i errors=0 element=0 counter=0 n L=2

# (2) Parse user input
until [[ -z "$1" || "$1" == '--' || "${1:0:1}" != '-' ]]; do
    [ "$Input" ] && unset Input
    if [[ "$1" =~ ^(-[Ww]|--[Ww]idth=)([0-9]+)? ]]; then
        Input=$(echo "$1" | gsed -re 's|--?W(idth=)?||I' | grep -Eoe '^(0|[1-9][0-9]*)$')
        [ -z "$Input" ] && echo "$2" | grep -Eoe '^(0|[1-9][0-9]*)$' && Input="$2" && shift 1
        (( Input >= 0 )) && Width="$Input" || unset Width
    elif [[ "$1" =~ ^((-[LlIi]|--(([Ll]ead(er|ing)?)?([Ii]n(dent)?)|[Ll]ead(er|ing)?)=)([0-9]+)?)$ ]]; then
        Input=$(echo "$1" | gsed -re 's|--?[a-z]+=?||I' | grep -Eoe '^(0|[1-9][0-9]*)$')
        [ -z "$Input" ] && echo "$2" | grep -Eoe '^(0|[1-9][0-9]*)$' && Input="$2" && shift 1
        (( Input >= 0 )) && L="$Input" || unset L
    ...
    else printf "$(Bold 'Error:') Unrecognized option: '$(Tbrown "$1")'\n\n" >&2
        exit 2
    fi
    shift 1
done

#(3) Now here, get text
IFS=''
[ -n "${*}" ] && declare Text="${*}" || Text="$(cat)" ## could also use read instead of cat ##
[ -z "$Text" ] && printf "$(Bold 'Error:') No text entered...\n\n" >&2 && exit 2

# (4) Process the text
Text="$(echo "$Text" | gsed -rne '1h;1!H;$g;s|[\x0A-\x0D]+| |g;$p' | expand -t4 )"
echo "$Text"    ##  (temporary)   ##
exit 0          ##  (temporary)   ##
...             ## (process text) ##
...             ## (process more) ##

Part 3 works for accepting text as entered after options and when piped, but hangs waiting for input if no text is entered and doesn’t see text passed as process substitution… eg:

Examples:

./myScript.sh -L10 --width=20 'This is a test'

> This is a test


echo 'This is a test' | ./myScript.sh -L10 --width=20

> This is a test


./myScript.sh -L10 --width=20 < <( echo 'This is a test' )

> This is a test


./myScript.sh -L10 --width=20       ##*** Want to stop this ***##

> (No output)... hangs waiting on cat (or read) for a ^D


echo 'This is a test' >( ./myScript.sh )

> This is a test /dev/fd/63
> <B>Error:</B> No text entered...


./myScript.sh -L10 --width=20 <<<'This is a test'

> This is a test


echo "This is a test" | tee >( ./myScript.sh -L10 --width=20 ) >( ./myScript.sh  )

> This is a test

> This is a test

> This is a test

How do I get the script to not hang on cat or read, waiting for input? (withoout using timeout or read -t as that just slows things down)?

Answer 1

I think what you want here is to avoid reading from a terminal:

if test -t 0; then
    echo "Not reading from terminal.  Pipe through cat if you really want to do this" >&2
    exit 1
fi

It is not possible to detect the general case where no source of input has been provided specifically to the program; all redirection is done by the shell, and your program cannot tell if its standard input was given specifically to it or inherited from the shell.