Menu
I want to be able to tell if a command exists on any POSIX system from a shell script.
On Linux, I can do the following:
if which <command>; then ...snip... fi However, Solaris and MacOS which do not give an exit failure code when the command does not exist, they just print an error message to STDOUT.
Also, I recently discovered that the which command itself is not POSIX (see http://pubs.opengroup.org/onlinepubs/9699919799/idx/utilities.html)
Any ideas?
611
You can use the posix compatible command to check, if the command exists from a bash script or not. if it returns >0 when the command is not found or an error occurs. similary you can use type and hash .
Use the command -v Command to Check if a Command Exists in Bash. The command -v is a built-in function in all POSIX systems and Bash. This function checks if a command exists as it returns the valid path for that command if it does exist and returns NULL if it does not.
POSIX is shorthand for Portable Operating System Interface. It is an IEEE 1003.1 standard that defines the language interface between application programs (along with command line shells and utility interfaces) and the UNIX operating system.
command -v is a POSIX specified command that does what which does.
It is defined to to return >0 when the command is not found or an error occurs.
125
You could read the stdout/stderr of "which" into a variable or an array (using backticks) rather than checking for an exit code.
If the system does not have a "which" or "where" command, you could also grab the contents of the $PATH variable, then loop over all the directories and search for the given executable. That's essentially what which does (although it might use some caching/optimization of $PATH results).
24
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With
