The literal answer is as others have given: because the current directory isn't in your $PATH.
But why? In short, it's for security. If you're looking in someone else's home directory (or /tmp), and type just gcc or ls, you want to know you're running the real one, not a malicious version your prankster friend has written which erases all your files. Another example would be test or [, which might override those commands in shell scripts, if your shell doesn't have those as built-ins.
Having . as the last entry in your path is a bit safer, but there are other attacks which make use of that. An easy one is to exploit common typos, like sl or ls-l. Or, find a common command that happens to be not installed on this system — vim, for example, since sysadmins are of above-average likelyhood to type that.
Does this sound too theoretical? It largely is, but it definitely can happen in reality, especially on multi-user systems. In fact, here is an example from this site where an administrator switched to a users' home directory and found ps to be masked by an executable of that name.
Quora
How to run a file in terminal using Linux - Quora
Answer (1 of 6): [code ]./path/to/file/file_name.extension[/code] For the various other possible cases, you’ve provided too little information, which hopefully teaches you to provide context, logs and/or examples.
Stack Overflow
linux - how to run/execute a file in the command line without the ./ - Stack Overflow
For example, this is a part of my "$PATH": /usr/local/bin:/usr/bin:/bin:/usr/local/sbin:/usr/sbin:/sbin:/home/rany/bin ... After putting an executable script in one of these directories you'll be able to execute it by simply typing its name at the command line.
How can i run a downloaded file?
r/linux4noobs • 21 • March 9, 2023
How can i run a downloaded file?
21
• March 9, 2023you should give more details. you extract the files from the archive, then what to do next totally depends on the files that were in the archive. so extract the files, and give more details. More on reddit.com
How to execute sh files on linux
r/linux4noobs • 6 • June 26, 2021
How to execute sh files on linux
6
• June 26, 2021if the file.sh isn't marked executable yet, do a chmod +x file.sh after that, just ./file.sh to run it HTH More on reddit.com
How to run .bin file?
r/linux • 15 • September 17, 2013
How to run .bin file?
15
• September 17, 2013chmod +x foo.bin ./foo.bin More on reddit.com
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running executables in terminal
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