On Mon, 22 Dec 2008, Gabe Turner wrote:
> On Fri, Dec 19, 2008 at 06:09:59PM -0600, Mike Miller wrote:
> [snip]
>> Have any of you done this kind of thing before? Let me know if you know
>> of code for converting scripts or have ideas on how to make the thing
>> below do more or work better.
>
> I don't know about your scripts, but most of the ones I write have a
> bunch of if statements and cases in them. Such statements can be a bit
> tricky in bash at first due to all of the implicit typing. A few
> pointers:
>
> if [[ ... ]]; # this is a conditional expression
>
> Example:
>
> if [[ $foo == "bar" ]]; then echo $foo; fi
>
> if (( ... )); # this is an arithmetic expression
>
> Example:
>
> if (( $num < 10 )); then echo "Oops!"; exit; fi
>
> (( )) is also a nice way to do boolean conditions in bash, I've found.
> let's say you want to exit if a command has failed:
>
> mv foo bar;
>
> if (($?)); then "Couldn't rename foo!"; exit 1; fi
>
> $? is the exit status of the last command run. If it's 0, i.e. the last
> command exited without error, the if will be false.
Thanks, Gabe.
I didn't use many "if" statements in my tcsh scripts though I have used
them more often in bash scripts, so my need to translate "if" from tcsh to
bash is not strong, but I might add a few lines to my little translator.
See man page sections below. I could at least change "else if" to "elif",
put semicolons in the right places, change "endif" to "fi" and a few other
things to make it easier to convert.
Thanks for the idea. I suppose there are also "while" loops to deal with.
P.S. I don't suppose "tcsh" stands for "Twin Cities SHell"?! OK, I know
it doesn't. The "c" stands for "C" and the "t" stands for "TENEX."
Best,
Mike
TCSH:
if (expr) command
If expr (an expression, as described under Expres-
sions) evaluates true, then command is executed.
Variable substitution on command happens early, at
the same time it does for the rest of the if
command. command must be a simple command, not an
alias, a pipeline, a command list or a parenthesized
command list, but it may have arguments.
Input/output redirection occurs even if expr is
false and command is thus not executed; this is a
bug.
if (expr) then
...
else if (expr2) then
...
else
...
endif If the specified expr is true then the commands to
the first else are executed; otherwise if expr2 is
true then the commands to the second else are exe-
cuted, etc. Any number of else-if pairs are possi-
ble; only one endif is needed. The else part is
likewise optional. (The words else and endif must
appear at the beginning of input lines; the if must
appear alone on its input line or after an else.)
BASH:
if list; then list; [ elif list; then list; ] ... [ else list; ] fi
The if list is executed. If its exit status is zero, the
then list is executed. Otherwise, each elif list is exe-
cuted in turn, and if its exit status is zero, the corre-
sponding then list is executed and the command completes.
Otherwise, the else list is executed, if present. The exit
status is the exit status of the last command executed, or
zero if no condition tested true.