help with shell programming

[squelchwelly]

Hello,
I just started working through "Beginning lInux Programming" by Matthew and Stones and am having difficulty getting one of their sample scripts to run. Using vi and bash, I typed this in from page 36, and called it tryifthree. It is supposed to demonstrate the elif construct:

#!/bin/sh

echo "Is it morning? Please answer yes or no"
read timeofday

if [$timeofday = "yes" ]
then
echo "Good morning"
elif [$timeofday = "no" ]; then
echo "Good afternoon"
else
echo "Sorry, $timeofday not recognized. Enter yes or no"
exit 1
fi

exit 0

and when I run it I get

rodmac@cherry:~/practiceprogs$ ./tryifthree
Is it morning? Please answer yes or no
yes
./tryifthree: line 6: [yes: command not found
./tryifthree: line 9: [yes: command not found
Sorry, yes not recognized. Enter yes or no

If I type in "no" I get a similar error message saying, no: command not found.
I looked over it lots of times and cannot see why it should not run so I downloaded the source code from wrox.com. They call it elif1 and when I run that I get a different error:

bash: ./elif1: /bin/sh^M: bad interpreter: No such file or directory

Then I copied and pasted it into gedit, saved it and ran it. I got the same error about a bad interpreter.
I am a beginner to shell programming and would be grateful for any help because I am completely flummoxed. I started out full of optimism because it looked like this book would explain lots of things about Linux programming that I wanted to know about. My impression of Ubuntu so far is that it is brilliant; everything has worked so far! I had hoped to scale the heights of programming but I cannot even tie my bootlaces.
Thanks.

[ubuntumaneh]

Instead of:
if [$timeofday = "yes" ]

you should use:
if [$timeofday == "yes" ]

The same for:
Use:
elif [$timeofday == "no" ];


Now, I believe you are not in a POSIX enviroment, so this little mistake will raise that exception. Try it.

[LordHunter317]

You need a space between the '[' and the command. As for the other error, it looks like your newlines are something other than what the shell expects, you didn't save this as like a mac file, did you?

[heimo]

Put space after [ in if statements:

#!/bin/sh

echo "Is it morning? Please answer yes or no"
read timeofday

if [ $timeofday = "yes" ]
then
echo "Good morning"
elif [ $timeofday = "no" ]; then
echo "Good afternoon"
else
echo "Sorry, $timeofday not recognized. Enter yes or no"
exit 1
fi

exit 0

[LordHunter317]

Now, I believe you are not in a POSIX enviroment, so this little mistake will raise that exception. Try it.No, what he wrote won't do that.

[jrib]

if [$timeofday = "yes" ]

elif [$timeofday = "no" ]; then


change that to:


if [ $timeofday = "yes" ]

elif [ $timeofday = "no" ]; then


notice the space after the [, as for your second question, seems there are stray ^M chars in your file, the command sed -i 's/^M//g' /path/to/script.sh should take care of them
and you enter the '^M' by hitting ctrl-v and then ctrl-m

[edit] too slow :)

[jrib]

after reading what lordhunter said, you may need to use 's/^M/\n/g' in the sed command above insteadm since mac files use new lines like that instead of using \n

try both and let us know what works, or if both fail :)

[lcg]

Hello,
I just started working through "Beginning lInux Programming" by Matthew and Stones and am having difficulty getting one of their sample scripts to run.
...
I am a beginner to shell programming and would be grateful for any help because I am completely flummoxed.
Try this one
#!/bin/sh

echo "Is it morning? Please answer yes or no"
read timeofday

if [[ $timeofday == "yes" ]]; then
echo "Good morning";
elif [[ $timeofday == "no" ]]; then
echo "Good afternoon";
else
echo "Sorry, $timeofday not recognized. Enter yes or no";
exit 1;
fi

exit 0

Your problem came from the fact that [ is a builtin command for bash. You didn't have a space between [ and your variable, so after bash substituted the value for the variable, there was a new word which bash didn't know how to interpret ([yes).
There were several ; missing, I used [[ ]] instead of [ ] (read 'man bash' for the reasons) and == for string comparison (which is not really necessary, I just like to be able to distinguish comparison from assigning a value to a variable).

HTH,
Lars

[squelchwelly]

Aaaargh - poke me in the eye! I knew about the space after [ because Matthew and Stones do mention it. I might have spotted the mistake if the version I downloaded had run. I don't know anything about sed yet but I tried
sed -i 's/^M//g' /path/to/script.sh
by doing this in the directory containing the script:
sed -i 's/^M//g' ./elif1
Nothing much seemed to happen, which I gather can be a good sign - no error messages. However running the script still gives the error message
bash: ./elif1: /bin/sh^M: bad interpreter: No such file or directory
So I tried the other version
sed -i 's/^M/\n/g' ./elif1
but with the same (lack of) results.
I didn't get the file from a mac. Using vi to look at the download version I see "(dos)" in the status bar after the file name but I don't see any instances of ^M. However when I use vi to look at the version I made by copying and pasting the downloaded version I see ^M at the end of each line but no "(dos)" in the status bar. The sed commands you guys showed me seem to have no effect on it.
But the version I typed in by hand works so thanks for the help. I can hardly believe how quickly I got a response. It sure would be handy to be able to make these downloaded files work so any advice on this would be gratefully accepted.
Thanks
Roddy

[jrib]

did you make sure to enter '^M' by pressing ctrl-v and then ctrl-m and not ^ followed by M? I think you can also use '\r' instead of '^M', so you may want to try that too

If these don't work it might be helpful to attach the file that is giving you problems

[jerome bettis]

I used [[ ]] instead of [ ] (read 'man bash' for the reasons)
i've never seen [[ ]] before, and i'm too lazy to sift through that (giant!) manual ... could you briefly explain the advantage of using double instead of single brackets?

[squelchwelly]

Mea culpa! I thought I would get away with copying and pasting these arcane looking sed commands. Now I have tried them by typing ctrl v and ctrl m like jason suggested and they both work! Thanks a bundle- there are hundreds of programs in the download file so the sed commands will be really useful.
On another point about using "==" instead of "=" I tried this and the script worked without giving any error messages. So I think I'll adopt this to distinguish comparison form assignment.
My optimism is restored
Thanks
Roddy

[lcg]

i've never seen [[ ]] before, and i'm too lazy to sift through that (giant!) manual ... could you briefly explain the advantage of using double instead of single brackets?
From 'man bash':
[[ expression ]]
Return a status of 0 or 1 depending on the evaluation of the
conditional expression expression.

I have always used [[ ]] for comparison and never really questioned it. I googled a bit (ever tried to make Google accept [[ as search term?) and found this page (http://www.medife.com.ar/LDP/LDP/abs/html/testconstructs.html). Very far down the page, it says: "The [[ ]] construct is the more versatile Bash version of [ ]. This is the extended test command, adopted from ksh88." and "Using the [[ ... ]] test construct, rather than [ ... ] can prevent many logic errors in scripts. For example, the &&, ||, <, and > operators work within a [[ ]] test, despite giving an error within a [ ] construct."

HTH,
Lars

[lcg]

On another point about using "==" instead of "=" I tried this and the script worked without giving any error messages. So I think I'll adopt this to distinguish comparison form assignment.
I've always been fond of languages which made that distinction. It makes code much easier to read and maintain, which IMO is really important. However, for POSIX compliance bash also accepts = as comparison, AFAIK.

Actually, I've always liked programming languages where the syntax is clean, the compiler can actually give helpful error messages and a very strict type and range checking is done at compile time. For these reasons I really love Ada (or VHDL for designing hardware).

Lars