Re: [Help-bash] Is there a way to read the first empty field in a TSV input?

[Evan Gates]

Greg Wooledge <address@hidden> wrote:

> On Thu, Sep 28, 2017 at 10:56:14AM -0500, Peng Yu wrote:
> > Hi,
> > 
> > The following example shows that the variable "a" gets the value of
> > "x" which is the 2nd field of the input. I'd like "a" to always get
> > the first field even it may be empty. Is possible with bash?
> > 
> > ~$ IFS=$'\t' read -r a b c <<< $'\t'x$'\t'y
> 
> Whitespace characters in IFS are treated differently than non-whitespace
> characters in IFS.
> 
> If your input file has whitespace characters as separators but you want
> them to be treated the same way that, say, colons are treated in
> /etc/passwd then you have a couple choices:
> 
> 1) Use a language other than bash.
> 2) Convert the separators into some other character that bash treats
>    the way you want.

A third option, manually loop. I ran into this recently writing a gopher
client in bash where the separator is tab and all other characters are
allowed IIRC. My solution was:


pack() {
    printf '%s\t' "$ft" "$disp" "$sel" "$host" "$port" "$search"
}

unpack() {
    local line
    IFS= read -r line
    for k in ft disp sel host port search; do
        printf -v "$k" %s "${line%%$'\t'*}"
        line=${line#*$'\t'}
    done
}

emg