Search notes:

Shell command: which

which XYZ searches the directories that are listed in the $PATH environment variable for an executable or script named XYZ and, if found, prints the path to the executable or script: 
$ which which
/usr/bin/which
If an executable or script is not found, which prints nothing.
If there are multiple executable or scripts, which only prints the first one found.
which ${progname} is equivalent to type -P ${progname}.

See also

Shell commands
whichpm: a cross-platform script that locates installed Perl modules by their package name.
The Windows executable where.exe and the PowerShell command get-command.

Index

Fatal error: Uncaught PDOException: SQLSTATE[HY000]: General error: 8 attempt to write a readonly database in /home/httpd/vhosts/renenyffenegger.ch/php/web-request-database.php:78 Stack trace: #0 /home/httpd/vhosts/renenyffenegger.ch/php/web-request-database.php(78): PDOStatement->execute(Array) #1 /home/httpd/vhosts/renenyffenegger.ch/php/web-request-database.php(30): insert_webrequest_('/notes/Linux/sh...', 1788339739, '216.73.217.21', 'Mozilla/5.0 App...', NULL) #2 /home/httpd/vhosts/renenyffenegger.ch/httpsdocs/notes/Linux/shell/commands/which(53): insert_webrequest() #3 {main} thrown in /home/httpd/vhosts/renenyffenegger.ch/php/web-request-database.php on line 78