How to "hide" an executable from a bash script?

Question

I want to test the output of a bash script when one of the executables it depends on is missing, so I want to run that script with the dependency "hidden" but no others. PATH= ./script isn't an option because the script needs to run other executables before it reaches the statement I want to test. Is there a way of "hiding" an executable from a script without altering the filesystem?

For a concrete example, I want to run this script but hide the git executable (which is its main dependency) from it so that I can test its output under these conditions.

Create a virtual machine that has no git in it.

bmargulies
– bmargulies

2015-06-28 11:40:24 +00:00
Commented Jun 28, 2015 at 11:40 — bmargulies
– bmargulies, Commented Jun 28, 2015 at 11:40

npostavs · Accepted Answer · 2015-06-28 12:08:34Z

10

You can use the builtin command, hash:

hash [-r] [-p filename] [-dt] [name]

Each time hash is invoked, it remembers the full pathnames of the commands specified as name arguments, so they need not be searched for on subsequent invocations. ... The -p option inhibits the path search, and filename is used as the location of name. ... The -d option causes the shell to forget the remembered location of each name.

By passing a non-existent file to the -p option, it will be as if the command can't be found (although it can still be accessed by the full path). Passing -d undoes the effect.

$ hash -p /dev/null/git git
$ git --version
bash: /dev/null/git: command not found
$ /usr/bin/git --version
git version 1.9.5
$ hash -d git
$ git --version
git version 1.9.5

answered Jun 28, 2015 at 12:08

npostavs

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2 Comments

akhan Over a year ago

It doesn't work for me on bash v5 - the correct binary keeps getting hashed. I think the actual usage for hash -p is here which is to create an alias for a binary not in system path. glenn's answer is the correct approach.

npostavs Over a year ago

@akhan Works here on bash 4.4.12, but maybe v5 updates the hash table if the file isn't found. glenn's anser will certainly be more reliable.

glenn jackman · Accepted Answer · 2015-06-28 12:09:44Z

4

Add a function named git

git() { false; }

That will "hide" the git command

To copy @npostavs's idea, you can still get to the "real" git with the command builtin:

command git --version

answered Jun 28, 2015 at 12:09

glenn jackman

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Comments

Sean Kelleher · Accepted Answer · 2015-06-28 11:49:52Z

1

Since we know the program is running in bash, one solution is to - instead of "hiding" the program - emulate the behaviour of bash in this circumstance. We can find out what bash does when a command isn't found quite easily:

$ bash
$ not-a-command > stdout 2> stderr
$ echo $?
127
$ cat stdout
$ cat stderr
bash: not-a-command: command not found

We can then write this behaviour to a script with the executable name, such as git in the question's example:

$ echo 'echo >&2 "bash: git: command not found" && exit 127' > git
$ chmod +x git
$ PATH="$PWD:$PATH" git
$ echo $?
127
$ cat stdout
$ cat stderr
bash: git: command not found

answered Jun 28, 2015 at 11:49

Sean Kelleher

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Comments

3v0k4 · Accepted Answer · 2024-07-09 20:58:58Z

0

I created unpath for that:

Usage: unpath UNCMD CMD

unpath runs CMD with a modified PATH that does not contain UNCMD.

Arguments:
  UNCMD the command to hide from PATH
  CMD   the command to run with the modified PATH

In your case, you would use it as follows:

unpath git ./script

answered Jul 9, 2024 at 20:58

3v0k4

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