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I have a series of command to execute. However I need to exit whenever 'command is not found' error occurs. So post execution check of output is not an option

The "$?" variable is equal zero when 'command is not found' and on success.

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4 Answers 4

Reset to default
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If this should be done from a script, it's natural to use a conditional to express this kind of behaviour:

asdf 2> /dev/null || exit 1
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4 Comments

this is actually the most simple and and clean way, ty
How about ls /this/file/does/not/exist 2>/dev/null ? ls command still exists.
@anishsane Of course. No one said that this would exclude other cases of command failures.
+1! I did not know that it is working even if the called program not exists.Thx!
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If the command is not found, the exit status should be 127. However, you may be using bash 4 or later and have a function called command_not_found_handle defined. This function is called if a command cannot be found, and it may exit 0, masking the 127 code.

Running type command_not_found_handle will show the definition of the function if it is defined. You can disable it by running unset command_not_found_handle.

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UPDATED

Try

[ -x "$executable" ] && echo "Command '$executable' not found" >&2 && exit 1

This will write an error to stderr and exit with 1 exit code.

If You have just the name of the utility You can check its path with type build-in.

Example:

type type type ls type xls

Output:

type is a shell builtin ls is /usr/bin/ls ./test.sh: line 13: type: xls: not found

Test returns 1 if utility not found.

So if the $executable can be anything (a build-in, alias, binary, ...), then this could be used:

type -p ls>/dev/null && ls -l type -p xls>/dev/null && xls --some_arg

This will run ls (any executable), but not xls.

Anyway if in the script the execfail option is not set (shopt) then the script will exit after stating the bash: some_utility: command not found error message. If this option is set, then it continues. But You can trap the pseudo signal ERR and do what You need:

shopt -s execfail fnc() { echo $?, $_, Oops;} trap fnc ERR ls -d *|head -2 xls yls

Output:

a1 a2 ./test_tLcn.sh: line 8: xls: command not found 127, xls, Oops ./test_tLcn.sh: line 9: yls: command not found 127, yls, Oops
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5 Comments

This will only work if $executable is a path to the executable you are looking for. -x does not perform path lookups.
@chapner: You are right! It does not detect internal bash commands. It could be done with e.g. type.
@chapner: I updated my answer according your comment. Pls take a look at it!
Trapping ERR seems overly broad, since that function will run on any error, not just a command-not-found error.
@chepner: Yes. But if $? is 127 then it can be detected that the command-not-found error occurred. $_ can be used to print the not found utility.
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Take jq as an example:

jq --version || echo "Please install [jq](https://stedolan.github.io/jq/download) first." && exit 1
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