File permissions

Who can do what

Every file has permissions that say who may read, write, or execute it.
ls -l shows them on the left of each line:

ls -l script.sh

You see something like -rwxr-xr-x. Read it in groups of three.

Reading the flags

The ten characters are: type, then owner, group, others:

-  rwx  r-x  r-x
file owner group others

r = read, w = write, x = execute, - = not allowed. So the owner here can do everything; others can read and run.

Changing permissions

chmod changes the mode. Numbers are a quick way: r=4, w=2, x=1, added per group:

chmod 755 script.sh

7 = 4+2+1 (rwx) for the owner; 5 = 4+1 (r-x) for group and others. 755 is the classic "runnable program".

Make script.sh runnable by giving it permissions 755 with chmod 755 script.sh. The check shows ls -l so you can see the new rwx flags.

# give script.sh permission 755

Click Run to see the output here.

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