Interactive multiple choice in a bash script

Question

Is there a simple way to let the user interactively choose one of the lines of the
output of lsblk -f?

NAME    FSTYPE LABEL        MOUNTPOINT
sda                         
├─sda1  ntfs   WINRE_DRV    
├─sda2  vfat   SYSTEM_DRV   
├─sda3  vfat   LRS_ESP      
├─sda4                      
├─sda5  ntfs   Windows8_OS  /media/Win8
├─sda6  ntfs   Data        /media/Data
├─sda7  ext4   linux        /
├─sda8                      
├─sda9  ntfs   4gb-original 
├─sda10 ntfs   PBR_DRV      
└─sda11 ext4   home         /home

And let the chosen line be filled in a variable to use in the continuation of the script?

I thought it would be perfect if the user could use the arrow keys to go up and down through the lines and press enter to select one. (I think I've seen this before in some configuration scripts during install.) If that's not possiple, at least how could I get numbers in front of each line to let the user choose using read?

I can't help you do that, but I can maybe guide you to relevant reading. I believe the interfaces you refer to in the configuration scripts are ncurses interfaces. — Joseph R.
– Joseph R., Commented Sep 26, 2014 at 3:25

rubo77 · Accepted Answer · 2014-09-26 19:43:52Z

You're looking for dialog. It's a very powerful tool and uses ncurses to provide a lot of options. I suggest you read through its manpage. Specifically, you want the --menu option:

   --menu text height width menu-height [ tag item ] ...
          As its name suggests, a menu box is a dialog  box  that  can  be
          used  to present a list of choices in the form of a menu for the
          user to choose.  Choices are displayed in the order given.  Each
          menu entry consists of a tag string and an item string.  The tag
          gives the entry a name to distinguish it from the other  entries
          in the menu.  The item is a short description of the option that
          the entry represents.  The user can move between  the  menu  en‐
          tries  by  pressing the cursor keys, the first letter of the tag
          as a hot-key, or the number keys 1-9. There are menu-height  en‐
          tries  displayed  in  the menu at one time, but the menu will be
          scrolled if there are more entries than that.

          On exit the tag of the chosen menu entry will be printed on dia‐
          log's  output.  If the "--help-button" option is given, the cor‐
          responding help text will be printed if  the  user  selects  the
          help button.

Unfortunately, implementing it in a sane manner using the output of a command that contains spaces is quite complex because of various quoting issues. At any rate, I didn't manage to do it, and had to resort to using eval. Nevertheless, it does work and does what you asked for:

#!/usr/bin/env bash
tmp=$(mktemp)
IFS=
eval dialog --menu \"Please choose a filesystem:\" 50 50 10 $(lsblk -f | sed -r 's/^/"/;s/$/" " "/' | tr $'\n' ' ') 2>$tmp
D=$(tr -d '│├└─' < $tmp | sed 's/^[ \t]*//' | cut -d' ' -f1)
printf "You chose:\n%s\n" "$D"

For a more portable approach, change the grep command to

The sed just formats the output of lsblk so that there are quotes around each output line (that's dialog's "tag"), followed by a quoted space (that's dialog's "item") and the tr replaces newlines with spaces and the tree-part-characters.

The result looks like this:

              ┌────────────────────────────────────────────────┐
              │ Please choose a filesystem:                    │  
              │ ┌────────────────────────────────────────────┐ │  
              │ │     NAME   FSTYPE LABEL MOUNTPOINT         │ │  
              │ │     sda                                    │ │  
              │ │     ├─sda1                                 │ │  
              │ │     ├─sda2                                 │ │  
              │ │     ├─sda3              /winblows          │ │  
              │ │     ├─sda4                                 │ │  
              │ │     ├─sda5                                 │ │  
              │ │     ├─sda6              /home              │ │  
              │ │     ├─sda7              /                  │ │  
              │ │     └─sda8              [SWAP]             │ │  
              │ └────↓(+)────────────────────────────90%─────┘ │  
              │                                                │  
              ├────────────────────────────────────────────────┤  
              │           <  OK  >      <Cancel>               │  
              └────────────────────────────────────────────────┘

@rubo77 the backslash is just there to make it fit in my answer. It is not needed. It works fine in bash but if putty is giving you problems, just put the whole dialog command on a single line, no backslash. As for the device, that's probably because of the non-ASCII characters there. You can try the grep from my other comment or one of D=$(sed 's/[^[:alnum:]]*//' $tmp) or D=$(sed 's/.*$...[0-9]\{1,2\}$.*/\1/') or D=$(perl -pe 's/^\W+//'). Alternatively, use the -i option for lsblk which makes it print ASCII only. — terdon
– terdon ♦, Commented Sep 26, 2014 at 11:30
Your examples all fail on some partitions like ´gb-original` or media/win8 But this will work fine: D=$(tr -d 'â├└─' < $tmp | cut -d' ' -f1) see my gist — rubo77
– rubo77, Commented Sep 26, 2014 at 16:30
@rubo77 done. I removed the echo $(tr ...) since that wasn't needed. — terdon
– terdon ♦, Commented Sep 26, 2014 at 18:14

Adam Freeman · Accepted Answer · 2014-09-26 03:34:48Z

Under normal operation, you can't change lines above the cursor -- they've already been flushed. The script you probably saw were probably using the curses library, so if you really want this I'd recommend using a scripting language like python and using the curses library there.

Putting numbers in front of each line is much easier. You can use this awk line to put numbers in front of them. There's probably a more elegant way, but this works. Alter the regex to suit your needs.

lsblk -f | awk 'BEGIN{disk=1;} /sd[a-z][1-9]+/ {print disk, ": ",$RT;disk=disk+1;next}{print "   ", $RT}'

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