use `true` builtin instead of `/bin/true` in bash

Question

I have written some code that uses the /bin/true by accident and I want to force the usage of the builtin of true and false.. any Idea what is the correct way of doing so?

#!/usr/bin/env bash
set -eEuo pipefail

CONFIRM=false
if [[ $1 == "Y" ]]; then
  CONFIRM=true
fi

"${CONFIRM}" || echo "Deletion will not happen, please run with '${0} Y' to confirm"

if $CONFIRM; then
 echo "I deleted the stuff!"
fi

This should use the built-in if it exists. That said, I don't think it matters. The only difference between the built-in and `/bin/true` would be whether a process is started, not in the exit status either produces. — chepner, Oct 19 '21 at 14:21
you can shorten the code a bit: `[[ $1 == Y ]] && confirm=true || confirm=false` — glenn jackman, Oct 19 '21 at 14:22
Get out of the habit of using ALLCAPS variable names, leave those as reserved by the shell. One day you'll write `PATH=something` and then [wonder why](https://stackoverflow.com/q/27555060/7552) your [script is broken](https://stackoverflow.com/q/28310594/7552). — glenn jackman, Oct 19 '21 at 14:22
and @chepner is right: bash looks for builtins before external commands. At a prompt, enter `type -a true`, and see [3.7.2 Command Search and Execution](https://www.gnu.org/software/bash/manual/bash.html#Command-Search-and-Execution) in the manual — glenn jackman, Oct 19 '21 at 14:24
@glenn-jackman the shorter code is more voodoo for some. The allcaps have been fixed in the original script — goergettica, Oct 20 '21 at 23:32

Ted Lyngmo · Answer 1 · 2021-10-21T09:43:19.130

2

To me, this looks like a job for if ... else:

#!/usr/bin/env bash
set -eEuo pipefail

if [[ $# -eq 1 && $1 == Y ]]; then
  echo "I deleted the stuff!"
else
  echo "Deletion will not happen, please run with '${0} Y' to confirm"
fi

If you need to save the result:

#!/usr/bin/env bash
set -eEuo pipefail

# with the set-mode above, you can set `conform` like this:
[[ $# -eq 1 && $1 == Y ]] && confirm=$? || confirm=$?
# otherwise, you could just set it after the above test

# truth test
[[ $confirm -eq $() ]] || echo "Deletion will not happen, please run with '${0} Y' to confirm"

# truth test again
if [[ $confirm -eq $() ]]; then
    echo "I deleted the stuff!"
fi

edited Oct 21 '21 at 09:43

answered Oct 19 '21 at 14:18

Ted Lyngmo

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Is `[[ $# -eq 1 && $1 == Y ]]` strictly equivalent to `[[ $1 == Y ]]` ? – Philippe Oct 19 '21 at 18:14
@Philippe No, not if `$1` is not assigned – Ted Lyngmo Oct 19 '21 at 18:16
If $1 is not assigned, `[[ $# -eq 1 && $1 == Y ]]` and `[[ $1 == Y ]]` give the same result. – Philippe Oct 19 '21 at 18:19
@Philippe Run bash in the same mode (the `set` line) and you should notice the diff if you don't supply any argument. – Ted Lyngmo Oct 19 '21 at 18:23
1

You are right, `-u` makes difference. – Philippe Oct 19 '21 at 18:28
The check is required in multiple places (simplified for the post here) – goergettica Oct 20 '21 at 23:34
@goergettica Ok, you could do like I showed in the alternative I added. – Ted Lyngmo Oct 21 '21 at 06:50

use `true` builtin instead of `/bin/true` in bash

1 Answers1