⚠ This page contains old, outdated, obsolete, … historic or WIP content! No warranties e.g. for correctness!
All 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40
Bernhard’s article on Plänet Debian about the “colon” command in the shell could use a clarification and a security-relevant correcture.
There is, indeed, no difference between the : and true built-in commands.
Stéphane Chazelas points out that writing : ${VARNAME:=default} is bad, : "${VARNAME:=default}" is correct. Reason: someone could preset $VARNAME with, for example, /*/*/*/*/../../../../*/*/*/*/../../../../*/*/*/* which will exhaust during globbing.
Besides that, the article is good. Thanks Bernhard for posting it!
PS: I sometimes use the colon as comment leader in the last line of a script or function, because it, unlike the octothorpe, sets $? to 0, which can be useful.
Update: As jilles pointed out in IRC, “colon” (‘:’) is a POSIX special built-in (most importantly, it keeps assignments), whereas “true” is a regular built-in utility.
