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Using grep with test and without using [[ ]]

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# 8  
Old 01-23-2019
Hi wisecracker,


please regard ;; as a fix syntax element to separate "cases". You can't use single semicolons as the "list" (in your man bash excerpt) can consist of several commands separated by ; .
These 2 Users Gave Thanks to RudiC For This Post:
wisecracker Xubuntu56
# 9  
Old 01-23-2019
Thanks RudiC...

That makes sense, I can see it in my minds eye now.
Sorry to tie up this thread with that question but it is useful for our new friend to know.

<Thumbs Up>
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Xubuntu56
# 10  
Old 01-23-2019
You could get away without tests, greps, square brackets, ifs, just using case ... esac:


Code:
case "$INT" in
   *[^0-9-]*)   echo no int;;
   -*[^0]*)     echo negative;;
   *[^-0]*)     echo positive;;
   *)           echo null;;
esac

The logics may need to be refined (e.g. to eliminate minus sign in the middle of the string), but should be doable.
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Xubuntu56
# 11  
Old 01-23-2019
@RudiC
The standard shell glob only mentions the ! as a negation of the following character set. The ^ is an extension in bash (and maybe some other shells).
Code:
case "$INT" in
   *[!0-9-]*|?*-*)   echo no int;;
   -[0-9]*)     echo negative;;
   [0-9]*)     echo positive;;
   *)           echo null;;
esac

@apmcd47
expr uses BRE that defines \{m,n\}
The GNU-extensions \? and \+ are generally \{0,1\} and \{1,\}
Unfortunately expr needs a work-around for a leading dash in its first argument
Code:
expr X"$INT" : X'-\{0,1\}[0-9]\{1,\}$'

And expr is an external command as well.

@wisecracker
You even posted the man page that mentions the list ;;
A list is a list of commands, separated with newline or ; (as usual).
Last edited by MadeInGermany; 01-23-2019 at 05:36 PM..
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apmcd47 RudiC
# 12  
Old 01-23-2019
@MadeInGermany: Thanks for pointing that out. I double checked before posting; man bash
Quote:
If the first character following the [ is a ! or a ^ then any character not enclosed is matched.
, and I (frequently but not always) test proposals on two systems (Linux and FreeBSD), but I'm afraid doing so on all possible systems / configurations is beyond me.


Thanks as well for extending the logics as I alluded to. Be aware that "-0" is identified as "negative" with your approach..
This User Gave Thanks to RudiC For This Post:
MadeInGermany
# 13  
Old 01-23-2019
Thanks to everyone!
Code:
#!/bin/bash

INT=9

if grep "^[-0-9]\+$" <<< "$INT"; then
    if test "$INT" -eq 0; then
        echo "INT is zero."
    else
        if test "$INT" -lt 0; then
            echo "INT is negative."
        else
            echo "INT is positive."
        fi
        if test $((INT % 2)) -eq 0; then
            echo "INT is even."
        else
            echo "INT is odd."
        fi
    fi
else
    echo "INT is not an integer." >&2
    exit 1
fi

# 14  
Old 01-24-2019
-0 feels slightly less than 0 Smilie

I have found now:
[!a-z] works in all Bourne-derived shells, only an interactive zsh does history substitution (and needs [^a-z] or "setopt no_bang_hist").
the [^a-z] works in ksh93 and dash-0.5.8 and zsh in addition to the [!a-z].

A curious example:
dash-0.5.8 has got the ^ in addition, but its man page still says
Quote:
The character class may be complemented by making
an exclamation point the first character of the character class.
@Xubuntu56
I do not understand why you want the builtin [[ =~ ]] replaced with grep but introduce the <<< operator that is again specific to bash.
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RudiC
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